JOURNAL OF PETROLOGY
VOLUME 52
NUMBER 12
PAGES 2483^2521
2011
doi:10.1093/petrology/egr053
Consequences of Channelized and Diffuse
Melt Transport in Supra-subduction Zone
Mantle: Evidence from the Voykar Ophiolite
(Polar Urals)
V. G. BATANOVA1,2,3*, I. A. BELOUSOV3, G. N. SAVELIEVA4 AND
A. V. SOBOLEV1,2,3
1
INSTITUT DES SCIENCES DE LA TERRE, UNIVERSITE J. FOURIER, GRENOBLE 1, 1381, RUE DE LA PISCINE,
38400 ST-MARTIN D’HERES, FRANCE
2
MAX-PLANCK-INSTITUT FU«R CHEMIE, ABT. BIOGEOCHEMIE, POSTFACH 3060, 55020 MAINZ, GERMANY
3
VERNADSKY INSTITUTE OF GEOCHEMISTRY AND ANALYTICAL CHEMISTRY, RUSSIAN ACADEMY OF SCIENCES,
KOSYGIN STR. 19, 119991, MOSCOW, RUSSIA
4
GEOLOGICAL INSTITUTE, RUSSIAN ACADEMY OF SCIENCES, PYZHEVSKII, 7, MOSCOW, 119017 RUSSIA
RECEIVED DECEMBER 22, 2010; ACCEPTED OCTOBER 7, 2011
The well-preserved, 6 km thick mantle section of the Voykar ophiolite
in the Polar Urals contains numerous dunite bodies as well as
dunite and pyroxenite veins within the host harzburgites. These
rocks provide evidence of a composite asthenosphere^lithosphere
history of partial melting, plastic deformation, multi-stage melt
migration and melt^rock interaction. We investigated the petrology
and geochemistry of multiple samples of the different mantle lithologies to define the sequence of mantle melting and melt migration
events, as well as the composition of the percolating melts. Spinel
harzburgites sampled far from dunite bodies and pyroxenite veins
have fairly homogeneous bulk-rock, olivine and Cr-spinel compositions and are interpreted as residues after 14^16% of partial melting, most probably at a mid-ocean ridge. Near the contacts with the
dunite bodies and pyroxenite veins, spinel peridotites demonstrate
distinct compositional changes marking different stages of melt
migration in a supra-subduction environment. At the earliest stage,
which probably took place in the lithosphere^asthenosphere boundary
of the forearc mantle at temperature between 1050 and 12008C and
a pressure of 1^1·7 GPa, the dunite bodies formed as a result of
stress-driven focused melt flow. The latest stage melts moved in
cracks under a conductive cooling regime within the lithospheric
mantle section when it was horizontally displaced towards the
*Corresponding author.Telephone: 33 (0)4 47 514104. Fax: 33 (0)4 76 51
40 58. E-mail: [email protected]
trench. The trace element composition of the melts that migrated
through the mantle section during dunite formation have geochemical
characteristics like those of high-Ca boninites. The role of the
slab-derived component progressively increased through time
and late-stage, pyroxenite-forming melts were conspicuously rich in
SiO2 and H2O. These low-viscosity melts impregnated the surrounding harzburgites, modifying or obliterating their primary
composition.
KEY WORDS: mantle peridotite; melt transport; dunite channels;
clinopyroxene; amphibole; boninite melts; supra-subduction
I N T RO D U C T I O N
Processes operating within the Earth’s upper mantle close
to the lithosphere^asthenosphere boundary control the
manner in which the lithosphere forms and evolves.
Numerous studies of ophiolitic and abyssal peridotites
published in the last two decades have convincingly
demonstrated that compositional heterogeneities observed
in mantle rocks are largely controlled by two main
ß The Author 2011. Published by Oxford University Press. All
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JOURNAL OF PETROLOGY
VOLUME 52
processes: partial melting and melt migration (e.g.
Rampone et al., 1997, 2008; Batanova et al., 1998; Parkinson
& Pearce, 1998; Batanova & Sobolev, 2000; Hellebrand
et al., 2002b; Piccardo, 2003; Seyler et al., 2004, 2007;
Brunelli et al., 2006; Piccardo et al., 2007). Whereas the
effects and extent of partial melting are relatively easy to
decipher from petrological indicators (e.g. Dick & Bullen,
1984; Hellebrand et al., 2001), the compositional changes of
mantle peridotites imposed by magma migration depend
mainly on the mechanisms of melt transport and the
composition of the migrating melts (e.g. Carlson, 1992).
Recent studies suggest that the porous flow of melt is
the dominant mode of melt migration in the mantle
(e.g. McKenzie, 1984). On the other hand, it is widely
accepted that melt extraction from the mantle beneath
mid-ocean ridges (MOR) occurs by focused flow along
chemically isolated channels (e.g. Nicolas, 1986, 1990;
Spiegelman & Kenyon, 1992; Hart, 1993; Kelemen et al.,
1995a). In their pioneering work, Kelemen and co-authors
showed that mantle dunites form by the complete dissolution of pyroxene in peridotite during reactive melt
flow along high-permeability channels (e.g. Aharonov
et al., 1995; Kelemen et al., 1995a, 1995b, 1997). The transition
from diffuse porous melt flow to channel flow is assumed
to occur as a result of reactive infiltration instability
(e.g. Daines & Kohlstedt, 1994; Kelemen et al., 1997)
and/or under the influence of stress (e.g. Stevenson, 1989;
Holtzman et al., 2003; Holtzman & Kohlstedt, 2007;
Kohlstedt & Holtzman, 2009). The results of experiments
suggest that dunite channels form beneath mid-ocean
ridges at pressures from 1·25 to 0·5 GPa (Lambart et al.,
2009). At pressures higher than 1·25 GPa, diffuse porous
flow seems to prevail, and at pressures below 0·5 GPa
(within the crust), flowage is dominantly along open
fractures. Focused magma ascent does not rule out diffuse
porous flow of small amounts of melt at low melt/rock
ratios in the shallow mantle, the process that leads to melt
impregnation and refertilization of mantle peridotites
(e.g. Dijkstra et al., 2003; Brunelli et al., 2006; Seyler et al.,
2007; Rampone et al., 2008).
Many ophiolites are thought to form during rifting in
supra-subduction zone (SSZ) settings (forearc, immature
island arc or back-arc) (e.g. Dilek, 2003; Pearce, 2003).
In such settings, the flowage of fluid and/or melt flux
derived from the subducted slab will be influenced by the
thermal structures of the SSZ mantle. The input of these
fluids induces melting in the mantle wedge and changes
(weakens) its rheology.
The mantle sections of SSZ ophiolites commonly display
structures resulting from asthenospheric high-temperature
plastic flow or reaction between migrating melts and the
surrounding mantle peridotite. Additionally, they provide
information about mantle melting and melt transport in
the mantle wedge. Mapping and sampling of SSZ ophiolite
NUMBER 12
DECEMBER 2011
mantle sections is especially important because the study
of mantle material from modern subduction settings is
otherwise restricted to xenoliths in arc-related lavas or
forearc peridotites dredged on the ocean floor or recovered
from drill cores (e.g. Ishii et al., 1992; Parkinson & Pearce,
1998; Pearce et al., 2000; Parkinson et al., 2003; Ionov,
2010). Such sets of samples do not allow the investigation of the spatial relationships between the various
lithologies or the scale and distribution of mantle
heterogeneities.
Here we describe the petrology, mineralogy and
trace-element geochemistry of clinopyroxenes and amphiboles from the mantle section of the northern part of
the Voykar ophiolite in the Polar Urals. The following
features of Voykar ophiolite demonstrate that it represents
a unique geological setting (e.g. Savelieva et al., 2007). It
comprises extensive continuous sections of well-exposed
and exceptionally fresh mantle peridotite; numerous,
well-preserved outcrops of the crustal section of layered
olivine^pyroxene rocks, layered gabbro^norite, isotropic
hornblende gabbro, dolerite dike complexes and metamorphic rocks of eclogite^glaucophane, amphibolite,
blueschist and albite^lawsonite facies in the soles of the
ophiolitic allochthons. However, despite the fact that the
main geological features and particularly the plastic
deformation structures of the mantle section of the
Voykar ophiolite have been well studied since the 1980s
(e.g. Savelieva et al., 1980; Savelieva, 1987), chemical
analysis of the mantle lithologies performed with modern
techniques is limited to the determination of Sm^Nd and
Rb^Sr isotopic compositions and the rare earth element
contents of four harzburgite samples (Sharma et al., 1995;
Sharma & Wasserburg, 1996). Here we use new data to
investigate the nature of mantle melting processes, reactive
melt transport and melt^peridotite interaction processes,
and their role in the origin and distribution of mantle
heterogeneities in the SSZ mantle wedge as well as the
origin and composition of migrating melts.
G E O L O G I C A L B AC KG RO U N D
A N D M A N T L E S T RU C T U R E S
The Voykar complex is one of the best exposed and largest
ophiolites in the Urals with a strike length of over 200 km
(e.g. Saveliev & Savelieva, 1977; Yefimov et al., 1978;
Savelieva, 1987). According to traditional geodynamic
reconstructions for the Polar sector of the Uralides,
ophiolites represent oceanic lithosphere that formed in
Early^Middle Paleozoic back-arc and inter-arc marginal
basins (Saveliev, 1996; Savelieva et al., 2002). The ophiolites
and overlying and intruding island-arc complexes were
thrust over the continental margin (sedimentary shelf
complexes and sedimentary^volcanic complexes of the
continental slope) of the East European Platform in the
2484
BATANOVA et al.
MELT TRANSPORT IN SSZ MANTLE
Fig. 1. (a) Map showing the geographical position of the Voykar ophiolite. (b) Schematic geological map of the northern part of the Voykar
ophiolite; rectangle indicates the location of (c). (c) Map showing the detailed study area in the upper reaches of the Khoyla river (modified
after Savelieva et al., 1980, 2008). Areas (R, K and G) outlined by dashed lines represent the main sampling localities referred to in Table 1.
Late Paleozoic (Saveliev & Samygin, 1980; Puchkov, 2002;
Savelieva et al., 2002). The Voykar ophiolite (Fig. 1a and b)
comprises a mantle peridotite section (up to 6 km thick)
and a crustal section. The crustal section is composed
of a layered dunite^wehrlite^clinopyroxenite complex
(up to 600 m in total thickness); gabbro, gabbro^norite
and olivine gabbro (up to 1100 m in total thickness); and
isotropic gabbros closely associated with a complex of
sub-parallel dolerite dikes (total thickness of the complex
is 1000 m of which 400 m is represented by dikes).
Recent dating of the mantle and crustal sections of
the Voykar ophiolite suggests that the two sections did not
form simultaneously. A U^Pb age obtained by sensitive
high-resolution ion microprobe analysis of zircons from
chromitites from the Voykar mantle section is 585 6 Ma
(Savelieva et al., 2006, 2007), whereas a U^Pb zircon age
for a plagiogranite found within the sheeted dyke complex
is 490 7 Ma (Khain et al., 2007). Tonalites intruding
the gabbros and dolerites in the eastern part of the
Voykar ophiolite (Fig. 1b), and marking early overthrusting
of the oceanic crust (Savelieva, 1987) have yielded an
Rb^Sr isochron age of 395 5 Ma (Buyakayte et al., 1983).
Thus, the magmatic processes occurring in the mantle
section were much older than the formation of the crust.
This is consistent with observations from other ophiolites;
for example, the Internal Liguride (Rampone et al., 1998),
Xigaze (Gopel et al., 1984), Trinity (Jacobsen et al., 1984;
Gruau et al., 1995) and Troodos ophiolites (Sobolev &
Batanova, 1995; Batanova & Sobolev, 2000; Buchl et al.,
2004) and demonstrates that some ophiolites consist of
mantle and crustal sections that are not genetically linked
by a simple melt^residue relationship.
The Vendian age of zircon from the chromitites
(Savelieva et al., 2006, 2007) and the Ordovician age of
zircon from the plagiogranites in the sheeted dike complex
suggest that the Paleozoic island-arc complexes of the
2485
JOURNAL OF PETROLOGY
VOLUME 52
NUMBER 12
DECEMBER 2011
Fig. 1. Continued.
Polar Urals are underlain by tectonically juxtaposed
fragments of Paleozoic and Late Proterozoic oceanic
lithosphere (Samygin & Ruzhentsev, 2003; Savelieva et al.,
2008).
Samples for this study were collected from the northern
part of the Voykar complex (Fig. 1b and c), which is
predominantly composed of mantle peridotites covering
an area 80 km long and 30 km wide. The sole of the peridotite sheet dips gently eastward, and the thickness of the
peridotite section increases from 0·5^0·8 km in the west to
6^8 km in the east. The mantle sequence is represented by
spinel peridotites, mainly harzburgites, with numerous
dunite bodies that make up about 20% of the peridotite
section (Savelieva, 1987; Savelieva et al., 2008). Chromitite
2486
BATANOVA et al.
MELT TRANSPORT IN SSZ MANTLE
Table 1: Description and petrological information for the samples studied
Sample
Rock
Description
Estimated modal composition
Al2O3
(%)
wr
Fo ol
Cr-no.
Mg-no.
fO2
(Yb)N
spl
op
FMQ
cpx
LOI
UTM N
UTM E
63 58·180
pu211/1
Spl Hz
no clear relations to veins
ol(68) op(25) cpx(4) spl(2) hb(1)
1·16
91·02
0·40
91·1
0·83
3·25
0·03
pu215/7
Spl Hz
no clear relations to veins
ol(76) op(20) cpx(2) spl(2)
1·02
90·73
0·29
90·8
0·63
5·02
4·35
pu6 10/2
Spl Hz
1 m from pxt S2 vein
ol(68) op(24) cpx(5) spl (2) hb(1)
1·38
90·66
0·29
90·7
0·39
5·74
3·87
pu6 13
Spl Hz
no clear relations to veins
ol(66) op(27) cpx(5) spl(2)
1·54
91·23
0·27
91·0
0·40
4·93
2·74
66 32·570
pu6 16/2
Spl Hz
no clear relations to veins
ol(72) op(22) cpx(4) spl(2)
1·20
90·82
0·33
91·1
0·06
3·49
0·55
66 34·074
63 59·094
pu6 54/1
Spl Hz
no clear relations to veins
ol(70) op(23) cpx(5) spl(2)
1·58
90·88
0·25
90·8
0·66
6·26
50·01
66 30·488
64 18·606
pu6 39/2
Spl Hz
relic in Du (S1) (Fig. 2c)
ol(68) op(27) cpx(2) spl(2) hb(1)
1·10
91·12
0·42
91·3
1·06
2·91
3·67
66 32·580
63 58·096
pu6 25/1
Spl Hz
no clear relations to veins
ol(70) op(23·5) cpx(4·5) spl(2)
1·32
90·58
0·29
90·6
0·56
4·80
7·08
66 32·724
64 00·993
pu6 12/2
Spl Hz
adj. web vein (S2)
ol(71) op(24) cpx(3) spl(2)
0·71
90·15
0·48
90·5
0·42
3·26
4·36
66 32·494
63 58·025
pu7 59/10c
Spl Hz
9 cm from pxt vein (S2)
ol(70) op(26) cpx(2) spl(2)
0·55
90·58
0·51
90·8
0·12
2·42
50·01
66 32·744
64 19·175
pu7 59/10d
Spl Hz
5 cm from pxt vein (S2)
ol(47) op(50) cpx(2) spl(1)
1·03
90·59
0·53
90·8
0·12
2·62
50·01
66 32·744
64 19·175
pu6 24/1
Spl Hz
no clear relations to veins
ol(570) op(25) cpx(55) spl(2)
n.a.
90·41
0·29
90·5
0·19
5·13
n.a.
66 33·033
64 00·829
pu6 35/2
Spl Hz
10 m from S1, S2 veins
ol(570) op(20–25) cpx(55) spl(2)
n.a.
91·01
0·26
90·9
0·12
4·91
n.a.
66 32·124
63 57·970
Profile: host harzburgite—dunite vein in the periphery of large dunite, first stage (S1) of melt percolation, (Fig. 2b), R
pu7 15c6
Spl Hz
20 cm from dunite vein
ol(470) op(420) cpx(41) spl(2)
n.a.
91·62
0·46
91·8
0·48
2·22
n.a.
66 32·570
63 58·129
pu7 15c5
Spl Hz
5 cm from dunite vein
ol(470) op(420) cpx(41) spl(2)
n.a.
91·42
0·46
91·7
0·36
2·65
n.a.
66 32·570
63 58·129
pu7 15c4
Spl Hz
adjacent to dunite
ol(470) op(420) cpx(41) spl(2)
n.a.
91·42
0·49
0·06
3·12
n.a.
66 32·570
63 58·129
pu7 15c3
Du
adjacent to Spl Hz
ol(495) spl(55) cpx(51)
n.a.
91·43
0·59
–
n.a.
1·02
4·23
n.a.
66 32·570
63 58·129
pu7 15c2
Du
10 cm from Spl Hz
ol(495) spl(55) cpx(51)
n.a.
91·43
0·65
–
1·00
3·54
n.a.
66 32·570
63 58·129
pu7 15c1
Du
15 cm from Spl Hz
ol(495) spl(55) cpx(51)
n.a.
91·59
0·66
–
1·18
3·28
n.a.
66 32·570
63 58·129
Dunites, first stage (S1) of melt percolation
pu6 39/1
Du
large body (Fig. 2c), R
ol(98·5) spl(1·5) cpx(51)
0·51
91·31
0·42
–
1·38
4·33
7·1
66 32·580
63 58·096
pu6 38/1
Du
large body, R
ol(98·3) spl(1·3) cpx(0·4)
0·47
92·53
0·53
–
0·71
7·31
4·88
66 32·574
63 58·139
pu6 37/1
Du
vein 20 cm, R
ol(495) spl(55) cpx(51)
n.a.
90·45
0·36
–
1·06
6·27
n.a.
66 32·574
pu6 41
Du
vein 20 cm, R
ol(495) spl(55)
n.a.
91·27
0·59
–
1·14
4·42
n.a.
66 32·568
63 58·140
pu7 13/1
Du
vein 20–30 cm, R
ol(495) spl(55) cpx(51)
n.a.
92·27
0·61
–
0·74
4·74
n.a.
66 32·547
63 58·300
pu6 35/1
Du
vein 30–35 cm, K
ol(495) spl(55) cpx(51)
n.a.
90·76
0·44
–
0·75
8·11
n.a.
66 32·124
63 57·970
pu215/4
Du
adjacent to Opxt vein
ol(97·3) spl(2) cpx(0·7)
0·40
90·38
0·32
91·1
0·07
5·91
7·59
63 59·220
pu6 21/1
Du*
large body, adj opxt vein, G
ol(94·5) spl(5·5)
0·82
88·88
0·70
–
1·21
–
1·99
66 34·337
pu6 23/1
Du
adjacent to Opxt vein, G
ol(99) spl(1)
0·28
90·96
0·70
–
1·63
–
3·92
66 34·206
63 59·970
pu6 26/1
Du
large body, G
ol(495) spl(55)
n.a.
92·24
0·68
–
1·66
–
n.a.
66 34·250
64 00·584
pu6 27/1
Du
large body, adj. Hz, G
ol(495) spl(55) cpx(51)
n.a.
91·47
0·68
–
1·47
2·50
n.a.
66 34·432
64 01·056
63 58·370
Profile: host harzburgite—20 cm thick composite dunite–pyroxenite vein, second stage of melt percolation (S2) (Fig. 2e), R
pu6 11/4
Spl Hz
adjacent to ZCV (S2)
ol(82) op(12) cpx(4) spl(2)
0·84
90·51
0·37
90·6
0·16
4·46
2·55
66 32·529
pu6 11/3c
Web
rim adjacent to Spl Hz
cpx(475) opx(520) ol(55) hb(51)
n.a.
89·97
0·36
90·0
0·14
3·70
n.a.
66 32·529
63 58·370
pu6 11/3d
Du
vein center
ol(495) cpx(55) spl(53)
n.a.
89·96
0·51
–
0·28
3·70
n.a.
66 32·529
63 58·370
63 57·925
Profile: host harzburgite—40 cm thick composite dunite–pyroxenite vein, second stage of melt percolation (S2) (Fig. 2f), K
pu6 33/5
Spl Hz
70 cm from ZCV
ol(71) op(25) cpx(1) spl(2) hb(1)
1·10
91·23
0·37
91·6
0·12
2·73
4·75
66 31·774
pu7 33/5
Spl Hz
40 cm from ZCV
ol(69·5) op(25) cpx(2·5) spl(2) hb(1)
1·47
91·50
0·29
91·6
0·78
6·26
4·13
66 31·772
63 57·915
pu6 33/4
Spl Hz
adjacent to ZCV
ol(66) op(25) cpx(5) spl(2) hb(2)
1·08
90·27
0·44
90·9
0·10
3·05
3·39
66 31·774
63 57·925
pu6 33/2
Web
adjacent to Spl Hz
cpx(65) op(23) ol(10) spl(2)
3·29
90·10
0·38
90·1
0·15
4·28
2·48
66 31·774
63 57·925
pu6 33/1
Web
band in Du, vein center
cpx(68·5) op(11·5) ol(17·8) spl(2·2)
3·34
90·21
0·38
90·0
0·10
4·26
2·25
66 31·774
63 57·925
pu7 33/3
Du
vein center
ol(96) cpx(2) spl(2)
0·65
90·31
0·46
–
0·46
3·70
6·65
66 31·772
63 57·915
pu6 33/3
Du
vein center
ol(95·4) cpx(1·4) spl(3·2)
0·93
90·56
0·51
–
1·02
4·00
6·15
66 31·774
63 57·925
pu7 33/1
Hb Cpxt
late vein cutting ZCV
cpx(4) op(11) ol(13·6) hb(75)
9·67
86·13
–
87·2
–
3·79
3·22
66 31·772
63 57·915
(continued)
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JOURNAL OF PETROLOGY
VOLUME 52
NUMBER 12
DECEMBER 2011
Table 1: Continued
Sample
Rock
Description
Estimated modal composition
Al2O3
(%)
wr
Fo ol
Cr-no.
Mg-no.
fO2
(Yb)N
spl
op
FMQ
cpx
LOI
UTM N
UTM E
Pyroxenite veins, second stage (S2) of melt percolation
pu7 59/10b
Opxt
cont. Cpxt, within Hz
op(73) cpx(6) ol(20) spl(1)
1·56
90·60
0·51
90·9
0·11
2·24
50·01
66 32·744
64 19·175
pu7 59/10a
Cpxt
vein 5 cm, within Hz
cpx(71) op(27) ol(1) spl(1)
2·43
90·47
0·55
90·8
0·11
2·27
0·19
66 32·744
64 19·175
pu 214/7
Web
vein, within Hz, R
cpx(66) op(28·5) ol(5) hb(0·5)
2·20
86·06
–
86·7
–
2·08
0·31
pu6 12/1
Cpxt
vein 70 cm, within Hz, R
cpx(85) op(13) hb(1) spl(1)
2·39
85·63
0·46
85·1
0·76
2·16
0·16
66 32·494
63 58·025
pu6 17/2
Cpx
vein 2–3 m within dunite,G
cpx(80) op(9) ol(9·5) hb(1) spl(0·5)
2·11
84–86
0·39
86·0
0·85
1·93
0·83
66 34·151
63 59·271
pu6 20/4
Cpxt
51 m, within dunite, G
cpx(86) op(12) ol(2) hb(tr.) spl(tr.)
2·15
85·96
0·44
87·2
1·48
1·79
0·36
66 34·446
63 59·193
pu6 7
Web
vein 50 cm within Hz, R
op(50) cpx(48) ol(1) hb(1)
2·22
84–85
–
86·1
–
2·28
0·42
pu6 5
Web
vein 50 cm within Hz, R
op(448) cpx(448) ol(53) hb(51)
n.a.
85–86
0·22
86·9
0·31
n.a.
n.a.
pu7 16/1o
Web
vein 25 cm within Hz, R
op(470) cpx(525) ol(55) hb(51)
n.a.
86·04
0·29
87·0
0·46
4·83
n.a.
66 32·587
63 58·093
pu7 14/2
Web
vein 15 cm within Hz, R
op(55) cpx(470) ol(420) hb(51)
n.a.
87·05
–
88·0
–
2·48
n.a.
66 32·578
63 58·119
pu7 31/1
Cpxt
v. 40 cm, Hz, (Fig. 2d), K
op(520) cpx(480) hb(51)
n.a.
–
0·52
86·5
–
1·56
n.a.
66 31·741
63 58·452
Concentration of oxides and loss on ignition (LOI) in wt %; Fo ol and Mg-number op ¼ 100 [(Mg/(Mg þ Fe2þ)]; (Yb)N, chondrite
normalized; Cr-number Spl ¼ Cr/(Cr þ Al); fO2 FMQ, oxygen fugacity relative to FMQ, after Ballhaus et al. (1991). Spl Hz, spinel
harzburgite; Du, dunite; Web, Opxt, Cpxt, websterite, ortho- and clinopyroxenite respectively; Hb Cpxt, pyroxenite containing more
than 50% magmatic magnesiohornblende; cont., contact; n.a., not analysed; —, phase not found; R, K and G, sampled areas shown in
Fig. 1c; pu7 10/59b, 1–2 cm thick rim of opx located between clinopyroxenite vein and host harzburgite; UTM N UTM E, Universal
Transverse coordinate system longitude and latitude; S1 and S2, early and late stages of melt percolation (see text).
*Du sample enriched by chromite.
pods and lenses are associated with the dunites. Systematic
structural mapping of the mantle section shows that the
peridotites record several plastic deformation episodes
that correspond to mantle processes associated with the
generation of oceanic lithosphere above a subduction zone
(Savelieva et al., 1980, 2008). The earliest stage of
near-horizontal plastic flow could correspond to an asthenospheric current flowing away from a ridge axis after
the rotation of the ascending flow. Similar flow patterns
are frequently observed in ophiolites belonging to the
‘harzburgitic sub-type’ (Ceuleneer et al., 1988). A second
stage of high-temperature plastic deformation has produced large-scale flow folds within the spinel peridotite as
a result of diapiric ascent of mantle material into the lithosphere. The dunite bodies (up to 10 km2 in size) are located
within the axial zones of these large-scale flow folds
formed by harzburgite banding (Fig. 1c). As indicated by
petrofabric analysis, it is clear that the dunite and surrounding spinel peridotite were deformed simultaneously
in the same stress field. It has been shown that the dunite
was produced by replacement of spinel peridotite during
peridotite^melt reaction. There are numerous signs of the
replacive origin of the dunite, such as the presence of
relics of spinel harzburgite within the dunite (Fig. 2a^c)
(Savelieva et al., 2008; Batanova & Savelieva, 2009). The
dunite bodies appear to have been formed in zones weakened by stress-driven melt migration (Savelieva et al.,
2008). Networks of cross-cutting dunite veins have been
documented in the marginal zones of the larger dunite
bodies (Savelieva et al., 2008).
Pyroxenite veins of highly variable morphology, size and
composition are widespread within the Voykar mantle
section, usually associated with large dunite bodies. Thick
pyroxenite veins extend into the surrounding harzburgites
for about 3 km from the large dunite bodies. The veins cut
both dunite and host harzburgite and could be related to
the latest stages of melt percolation (Savelieva et al., 2008).
Several generations of pyroxenite veins were recognized
within a single peridotite outcrop by Savelieva et al. (1980,
2008). A detailed description of the various generations of
veins, their compositional peculiarities and relationships
is beyond the scope of this paper and will be reported
elsewhere (Belousov et al., in preparation).
This study focuses on the two stages of melt percolation
observed in the Voykar mantle section: (1) an early stage
(S1) during which the large dunite bodies were formed,
and (2) a later stage (S2) when numerous pyroxenite and
zoned, composite dunite^pyroxenite veins were emplaced.
There probably was no abrupt interface between these
two stages.
SAMPLE DESCR I PTION A N D
P E T RO G R A P H Y
More than 50 samples of harzburgite, dunite and
pyroxenite were collected from an area in which a
2488
BATANOVA et al.
MELT TRANSPORT IN SSZ MANTLE
Fig. 2. Photographs of the field relationships between the mantle lithologies of the Voykar ophiolite indicating the locations of the samples:
(a) dunite vein network in harzburgite; (b) a 30 cm wide dunite vein within harzburgite; the numbers at the side of the holes refer to pu07-15
labelled samples in Tables 1^4; (c) a harzburgite relic within a large dunite body; (d) a coarse-grained pyroxenite vein in harzburgite;
(e, f) zoned composite dunite^pyroxenite veins (ZCV) in harzburgite. Geological hammer denotes the scale.
three-dimensional interconnected dunite vein network developed around large dunite bodies and penetrated into
the harzburgite (Fig. 2a) (Savelieva et al., 1980, 2008;
Batanova & Savelieva, 2009). To understand the compositional changes produced in the host peridotite during the
formation of dunite (S1) and pyroxenite veins (S2), we
sampled spinel harzburgite at different distances from S1
and S2 ‘intrusive’ bodies (Table 1). Samples were taken
from different parts of large dunite bodies (Fig. 1c and 2c),
along a profile through the surrounding harzburgite and a
2489
JOURNAL OF PETROLOGY
VOLUME 52
NUMBER 12
DECEMBER 2011
Table 2: Whole-rock compositions of Voykar mantle lithologies
Sample (pu): 211/1
215/7
6 10/2
6 13
6 16/2
6 54/1
6 39/2
6 25/1
6 12/2 7 59/10c 7 59/10d 6 39/1
6 38/1
6 41
215/4
6 21/1
6 23/1
Rock:
Spl Hz
Spl Hz
Spl Hz
Spl Hz
Spl Hz
Spl Hz
Spl Hz
Spl Hz
Spl Hz
Spl Hz
Spl Hz
Du
Du
Du
Du
Du
Du
SiO2
44·38
42·99
44·08
44·74
43·74
44·17
43·78
44·05
47·52
40·40
40·49
39·64
40·39
38·67
40·39
TiO2
0·02
0·02
0·03
0·02
0·02
0·03
0·02
0·02
0·02
0·01
0·02
0·01
0·02
0·02
0·02
0·02
0·01
Al2O3
1·16
1·02
1·38
1·54
1·20
1·58
1·10
1·32
0·71
0·55
1·03
0·51
0·47
0·74
0·40
0·82
0·28
MgO
44·45
45·94
43·91
43·60
44·77
44·04
44·31 44·36
44·92
45·46
41·75
49·20
50·45
48·83
48·11
46·25
49·45
45·06 43·75
FeO
7·89
8·58
8·19
7·64
8·19
7·97
7·78
8·38
8·90
8·58
7·84
8·63
7·51
8·83
9·50
11·49
8·87
MnO
0·13
0·14
0·14
0·12
0·13
0·13
0·13
0·13
0·14
0·13
0·14
0·13
0·12
0·14
0·14
0·16
0·13
CaO
1·24
0·67
1·56
1·61
1·21
1·34
0·87
1·30
0·85
0·55
0·89
0·33
0·12
0·26
0·17
0·12
0·17
Na2O
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
K2O
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
P2O5
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
Cr2O3
0·42
0·31
0·42
0·41
0·43
0·43
0·44
0·44
0·40
0·34
0·56
0·43
0·43
1·19
0·92
2·21
0·37
NiO
0·31
0·32
0·29
0·30
0·31
0·31
0·28
0·31
0·29
0·31
0·25
0·36
0·40
0·35
0·35
0·26
0·34
LOI
0·03
4·35
3·87
2·74
0·55
50·01
3·67
7·06
4·36
50·01
50·01
7·10
4·88
5·09
7·59
1·99
3·92
(ppm)
Sc
10
4
8
10
8
7
6
9
6
6
12
2
5
1
V
47
33
42
52
45
45
35
39
29
25
50
15
10
25
18
52
11
Cr
2724
1880
2482
2539
2595
2621
2508
2764
2225
2246
4106
2265
2487
6203
4399
12928
1898
Co
117
124
120
118
120
122
116
117
122
128
110
134
128
132
137
153
141
Ni
2358
2338
2126
2230
2385
2365
2078
2187
2064
2407
1820
2496
2859
2559
2497
2003
2449
Cu
Zn
n.d.
48
n.d.
47
n.d.
45
n.d.
n.d.
42
47
n.d.
46
n.d.
40
19
26
11
8
9
48
46
49
54
44
7 59/10b 7 59/10a
n.d.
n.d.
n.d.
39
b.d.l.
n.d.
3
n.d.
47
46
73
n.d.
45
Sample (pu): 6 11/4
6 33/5
7 33/5
6 33/4
6 33/2
6 33/1
7 33/3
6 33/3
7 33/1
214/7
6 12/1
6 17/2
6 20/4
6 7
Rock:
Spl Hz
Spl Hz
Spl Hz
Spl Hz
Web
Web
Du
Du
Hb Cpxt
Opxt
Cpxt
Web
Cpxt
Cpxt
Cpxt
Web
SiO2
42·38
44·68
44·28
45·11
49·74
49·57
40·04
39·38
50·28
51·36
52·54
53·52
53·19
52·73
53·27
53·84
TiO2
0·02
0·03
0·02
0·02
0·10
0·11
0·01
0·02
0·08
0·03
0·06
0·05
0·06
0·06
0·06
0·05
Al2O3
0·84
1·10
1·47
1·08
3·29
3·34
0·65
0·93
9·67
1·56
2·43
2·20
2·39
2·11
2·15
2·22
MgO
46·09
45·02
44·64
42·76
24·67
24·26
47·78
47·94
23·45
37·13
22·56
22·39
19·29
20·84
18·96
25·34
FeO
8·65
7·76
7·81
8·39
4·72
4·66
9·74
9·69
5·20
6·99
3·68
5·37
4·50
4·84
4·21
6·24
MnO
0·13
0·11
0·12
0·13
0·11
0·11
0·14
0·14
0·11
0·14
0·10
0·14
0·13
0·13
0·12
0·15
15·66
11·56
CaO
1·12
0·66
0·90
1·77
15·83
16·42
0·57
0·35
9·45
1·92
17·54
19·72
18·37
20·23
Na2O
0·02
b.d.l.
b.d.l.
b.d.l.
0·09
0·05
b.d.l.
b.d.l.
1·27
b.d.l.
0·11
b.d.l.
0·04
0·02
0·03
b.d.l.
K2O
0·01
b.d.l.
b.d.l.
b.d.l.
0·01
0·01
b.d.l.
b.d.l.
0·13
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
P2O5
0·02
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
b.d.l.
Cr2O3
0·43
0·32
0·46
0·46
1·24
1·33
0·72
1·18
0·25
0·61
0·86
0·56
0·60
0·80
0·89
0·49
NiO
0·29
0·31
0·31
0·29
0·18
0·14
0·35
0·38
0·10
0·26
0·12
0·10
0·08
0·10
0·08
0·10
LOI
2·54
4·75
4·13
3·39
2·48
2·25
6·65
6·15
3·22
n.d.
0·19
0·31
0·16
0·83
0·36
0·42
(ppm)
Sc
n.d.
4
7
10
53
54
3
46
18
49
50
60
51
56
43
V
n.d.
30
34
41
188
200
24
b.d.l.
32
185
65
162
156
186
149
160
140
3432
Cr
2865
1961
2698
2559
8605
9188
3541
5783
1802
4235
6217
3954
4271
5507
6301
Co
79
117
119
119
59
54
138
147
50
86
41
55
40
51
42
65
Ni
2187
2246
2203
2069
1294
1003
2450
2687
697
1868
870
777
572
750
592
728
11
4
187
115
77
148
9
241
120
336
188
263
248
183
45
44
34
31
46
48
30
43
23
30
24
24
20
38
Cu
25·5
Zn
67
n.d.
43
Oxides calculated on an anhydrous basis;
b.d.l., below detection limit.
2490
BATANOVA et al.
MELT TRANSPORT IN SSZ MANTLE
Table 3: Major and trace element compositions of olivines in Voykar mantle lithologies (sample numbers all prefixed pu)
Sample
n*
Fo
SiO2
CaO
FeO
CoO
MgO
NiO
MnO
Total
ny
Ca
Ni
Ti
211/1
20
91·02
40·66
0·006
8·83
0·016
50·23
0·391
0·129
100·29
3
43
3170
0·02
0·04
0·001
0·01
0·0002
0·10
0·002
0·0004
10
15
90·73
40·66
0·009
9·11
0·016
49·99
0·382
0·133
74
0·05
0·06
0·001
0·03
0·0002
0·14
0·001
0·0006
90·66
40·75
0·008
9·15
0·017
49·83
0·363
0·136
0·03
0·02
0·001
0·02
0·0002
0·04
0·001
0·0006
14
91·23
40·84
0·010
8·58
0·016
50·05
0·397
0·128
0·03
0·02
0·001
0·03
0·0002
0·03
0·001
0·0003
22
90·82
40·66
0·009
8·97
0·017
0·391
0·132
0·02
0·02
0·001
0·02
0·0002
0·02
0·001
0·0004
0·04
90·88
40·57
0·007
8·91
0·017
49·83
0·400
0·130
99·87
0·02
0·02
0·001
0·02
0·0003
0·03
0·001
0·0005
0·04
16
91·12
40·71
0·007
8·69
0·017
0·380
0·130
99·93
0·02
0·02
0·001
0·01
0·0003
0·04
0·001
0·0005
0·04
6
90·58
40·61
0·009
9·18
0·016
49·53
0·385
0·135
99·87
0·03
0·04
0·002
0·02
0·0005
0·05
0·001
0·0006
0·08
90·15
40·47
0·008
9·60
0·017
49·31
0·352
0·143
99·90
0·02
0·05
0·000
0·02
0·0006
0·03
0·001
0·0008
0·09
14
90·58
40·66
0·006
9·19
0·017
49·62
0·392
0·133
0·03
0·03
0·002
0·05
0·0001
0·05
0·002
0·0010
0·10
5
90·59
40·69
0·007
9·17
0·018
49·56
0·385
0·133
99·97
0·03
0·06
0·002
0·03
0·0007
0·05
0·007
0·0005
10
90·41
40·58
0·008
9·35
0·018
49·45
0·396
0·135
0·03
0·03
0·001
0·03
0·0003
0·04
0·002
0·0011
0·06
91·01
40·56
0·007
8·77
0·016
49·79
0·392
0·129
99·67
0·02
0·05
0·001
0·02
0·0003
0·05
0·003
0·0008
0·08
91·62
40·75
0·007
8·21
0·017
50·39
0·399
0·120
99·90
0·02
0·02
0·001
0·01
0·0002
0·04
0·001
0·0009
0·03
5
91·42
40·67
0·010
8·38
0·016
50·09
0·380
0·126
99·68
0·04
0·04
0·002
0·04
0·0002
0·09
0·003
0·0012
0·13
5
91·42
40·78
0·005
8·39
0·017
50·17
0·363
0·127
99·86
0·02
0·02
0·001
0·02
0·0004
0·05
0·002
0·0008
0·05
91·43
40·77
0·009
8·39
0·016
50·22
0·351
0·129
99·89
0·04
0·03
0·000
0·04
0·0004
0·05
0·001
0·0005
0·06
5
91·43
40·86
0·008
8·41
0·016
50·32
0·346
0·129
0·02
0·03
0·001
0·02
0·0005
0·05
0·001
0·0008
0·06
5
91·59
40·84
0·009
8·25
0·016
50·38
0·344
0·127
99·97
0·03
0·03
0·001
0·03
0·0007
0·05
0·001
0·0004
0·06
91·31
40·66
0·062
8·50
0·016
50·07
0·367
0·134
99·86
0·01
0·02
0·003
0·02
0·0002
0·04
0·001
0·0003
0·08
10
90·45
40·77
0·015
9·35
0·016
49·72
0·321
0·146
0·02
0·05
0·001
0·02
0·0003
0·05
0·001
0·0006
0·09
17
92·53
40·96
0·011
7·35
0·015
51·07
0·393
0·118
99·93
0·01
0·01
0·001
0·01
0·0002
0·02
0·001
0·0003
0·04
91·27
40·72
0·026
8·56
0·016
50·19
0·350
0·133
0·02
0·02
0·003
0·02
0·0003
0·05
0·002
0·0007
s
215/7
15
s
6 10/2
15
s
6 13
s
6 16/2
s
6 54/1
19
s
6 39/2
s
6 25/1
s
6 12/2
6
s
7 59/10c
s
7 59/10d
s
6 24/1
s
6 35/2
6
s
7 15C6
4
s
7 15C5
s
7 15C4
s
7 15C3
5
s
7 15C2
s
7 15C1
s
6 39/1
20
s
6 37/1
s
6 38/1
s
6 41
s
10
49·8
50
Cu
Zn
Mn
Sc
Co
V
Li
7·1
0·51
31·7
975
2·1
132
0·66
0·88
0·5
0·05
0·5
2
0·1
1
0·03
0·02
3048
6·4
0·51
38·5
1034
2·3
134
1·09
1·22
19
2
0·2
0·05
0·2
8
0·1
1
0·37
0·08
79
2673
8·9
6·3
0·63
36·7
1012
2·0
136
0·66
1·17
7
12
0·4
1·3
0·02
1·2
4
0·1
1
0·06
0·05
3
73
3072
3·7
0·78
30·5
984
2·1
133
0·72
0·83
7
15
0·1
0·03
0·1
3
0·02
0·3
0·06
0·15
4
84
3134
2·6
4·5
0·47
34·3
1028
2·4
138
0·75
1·00
18
24
0·2
1·0
0·02
1·3
6
0·1
2
0·08
0·09
57
3143
8·8
0·62
27·7
990
1·8
131
0·62
0·97
4
14
0·4
0·06
1·5
6
0·03
1
0·02
0·04
3
47
2941
2·5
0·60
33·3
992
1·6
133
0·41
0·99
3
6
0·1
0·03
0·7
5
0·1
0·3
0·005
0·07
3
56
3023
3·7
0·57
34·8
1030
1·7
135
0·48
0·87
10
15
0·3
0·03
0·2
6
0·1
0·1
0·02
0·09
54
2759
6·7
0·56
39·1
1111
2·0
137
0·46
1·32
9
2
0·4
0·06
1·1
7
0·1
0·4
0·05
0·08
47
2825
7·0
0·61
36·4
1022
2·0
135
0·44
1·04
11
22
0·3
0·01
1·9
8
0·04
1
0·03
0·05
64
3163
5·3
4·6
0·43
34·7
1059
2·1
145
0·75
1·19
2
33
0·8
1·0
0·01
1·9
13
0·1
1
0·06
0·05
56
3076
9·9
0·64
32·2
991
1·5
133
0·56
0·92
12
11
0·5
0·02
0·6
5
0·1
0·2
0·08
0·06
56
3049
4·9
4·0
0·43
34·8
946
1·6
127
0·48
0·82
12
4
0·4
1·6
0·03
1·3
5
0·1
1
0·05
0·11
3
60
2877
3·1
2·3
0·49
30·7
977
1·6
125
0·35
0·86
9
27
0·1
0·4
0·01
2·3
7
0·1
1
0·01
0·07
3
44
2797
5·3
3·2
0·43
34·1
994
1·9
128
0·38
1·02
15
20
0·3
1·3
0·05
0·7
7
0·2
1
0·04
0·08
65
2676
9·6
1·5
0·47
25·5
1000
2·7
122
0·23
0·99
12
22
0·9
0·1
0·01
3·1
10
0·1
2
0·02
0·09
3
46
2667
11·0
1·5
0·47
23·2
1001
2·6
123
0·19
1·22
2
9
0·6
0·4
0·01
0·8
5
0·1
1
0·01
0·07
3
53
2647
11·0
1·9
0·46
20·6
993
2·5
121
0·20
1·23
11
9
0·4
0·4
0·03
2·3
3
0·0
1
0·00
0·04
398
2990
9·4
3·9
0·51
37·9
1028
3·9
136
0·54
0·80
31
12
0·3
0·5
0·03
1·3
2
0·2
0·4
0·03
0·06
4
101
2691
13·1
3·3
0·52
20·6
1127
4·0
139
0·36
1·20
8
14
0·6
0·6
0·04
0·5
5
0·1
1
0·04
0·07
4
108
3161
14·1
2·8
0·50
26·6
908
3·0
127
0·36
0·98
14
47
0·7
0·8
0·04
3·3
2
0·1
2
0·04
0·10
216
2906
9·6
3·3
0·44
29·6
1035
3·6
139
0·37
1·11
40
30
0·4
1·0
0·03
2·5
8
0·1
1
0·05
0·03
0·15
100·31
3
0·17
100·25
3
0·05
100·00
0·04
100·00
100·03
3
3
3
Al
0·07
100·24
100·09
100·31
100·14
0·07
4
3
3
3
4
5
(continued)
2491
JOURNAL OF PETROLOGY
VOLUME 52
NUMBER 12
DECEMBER 2011
Table 3: Continued
Sample
n*
Fo
SiO2
CaO
FeO
CoO
MgO
NiO
MnO
Total
ny
Ca
Ni
Ti
7 13/1
6
92·27
40·57
0·004
7·59
0·015
50·84
0·372
0·115
99·51
3
29
2864
0·02
0·07
0·001
0·02
0·0005
0·04
0·001
0·0005
0·12
10
21
90·76
40·75
0·025
9·06
0·016
49·92
0·353
0·141
165
2977
16·2
0·03
0·01
0·002
0·03
0·0003
0·04
0·001
0·0010
0·04
10
18
0·9
90·38
40·51
0·014
9·37
0·017
49·38
0·366
0·142
99·80
98
2899
0·02
0·05
0·001
0·02
0·0004
0·03
0·001
0·0005
0·08
11
4
10
88·88
40·39
0·013
10·81
0·020
48·45
0·266
0·163
4
79
0·03
0·05
0·002
0·03
0·0002
0·05
0·001
0·0011
12
90·96
40·70
0·031
8·85
0·017
49·95
0·338
0·139
4
0·01
0·03
0·002
0·01
0·0002
0·03
0·001
0·0003
92·24
40·91
0·072
7·62
0·015
50·79
0·372
0·125
0·02
0·03
0·004
0·02
0·0004
0·03
0·001
0·0003
11
91·47
40·76
0·063
8·34
0·017
0·357
0·137
0·02
0·02
0·003
0·02
0·0002
0·05
0·000
0·0005
0·05
6
90·51
40·52
0·011
9·26
0·016
49·56
0·367
0·138
99·88
0·03
0·09
0·002
0·03
0·0003
0·10
0·003
0·0008
0·18
89·97
40·36
0·006
9·73
0·018
48·96
0·408
0·150
99·94
0·05
0·03
0·001
0·05
0·0006
0·05
0·003
0·0009
0·07
10
89·96
40·41
0·009
9·76
0·017
49·09
0·320
0·152
0·03
0·02
0·001
0·02
0·0004
0·03
0·001
0·0007
22
91·23
40·74
0·009
8·61
0·017
50·24
0·404
0·122
0·01
0·01
0·001
0·01
0·0002
0·04
0·001
0·0003
91·50
40·98
0·011
8·35
0·016
50·46
0·394
0·122
0·01
0·06
0·001
0·01
0·0003
0·06
0·001
0·0006
90·27
40·67
0·007
9·50
0·018
49·48
0·371
0·140
0·02
0·02
0·001
0·02
0·0003
0·03
0·002
0·0005
0·04
90·10
40·40
0·012
9·62
0·015
49·13
0·373
0·144
99·71
0·03
0·03
0·001
0·03
0·0006
0·05
0·007
0·0009
0·07
9
90·21
40·64
0·016
9·57
0·017
49·47
0·338
0·147
0·02
0·03
0·001
0·02
0·0004
0·02
0·001
0·0005
10
90·31
40·68
0·015
9·47
0·016
49·55
0·339
0·145
0·02
0·04
0·001
0·02
0·0003
20
90·56
40·69
0·011
9·23
0·016
0·02
0·03
0·001
0·02
0·0003
3
86·13
39·75
0·012
13·41
0·15
0·11
0·007
0·14
4
90·60
40·59
0·004
9·16
0·018
0·05
0·03
0·001
0·05
11
90·47
40·31
0·009
9·24
0·02
0·03
0·001
0·02
5
86·06
40·03
0·015
13·47
0·08
0·11
0·004
0·08
4
85·63
39·83
0·015
13·81
0·03
0·05
0·001
0·04
86·38
40·04
0·011
0·05
0·03
0·001
s
6 35/1
10
s
215/4
6
s
6 21/1
s
6 23/1
s
6 26/1
11
s
6 27/1
s
6 11/4
s
6 11/3c
10
s
6 11/3d
s
6 33/5
s
7 33/5
10
s
6 33/4
19
s
6 33/2
6
s
6 33/1
s
7 33/3
s
6 33/3
s
7 33/1
s
7 59/10b
s
7 59/10a
s
214/7
s
6 12/1
s
6 17/2
s
4
50·2
0·04
0·001
0·0006
0·333
0·139
0·03
0·001
0·0004
46·72
0·374
0·203
49·7
100·16
100·34
Cu
Zn
Mn
Sc
Co
V
Li
4·7
0·49
28·5
888
2·4
122
0·18
1·31
0·2
0·02
2·7
6
0·0
1
0·00
0·04
1·6
0·53
31·2
1098
3·6
137
0·37
1·12
0·6
0·03
0·6
4
0·0
0·2
0·04
0·06
5·9
0·60
30·4
1090
3·0
134
0·24
1·39
0·1
0·02
1·0
6
0·1
0·4
0·01
0·02
2063
5·7
0·38
32·5
1245
3·2
147
0·28
1·13
6
35
0·2
0·01
1·8
15
0·1
2
0·03
0·08
230
2672
5·7
1·9
0·43
41·9
1080
3·7
138
0·31
0·85
29
7
0·3
0·9
0·03
2·0
7
0·0
1
0·04
0·04
468
2951
7·9
3·0
0·43
32·1
966
3·9
129
0·32
0·96
38
12
0·6
0·3
0·04
0·4
2
0·2
0·4
0·01
0·05
412
2867
7·9
3·2
0·42
40·8
1063
3·8
133
0·41
0·97
22
15
0·5
0·5
0·01
1·2
6
0·1
1
0·05
0·07
59
2872
6·3
0·66
33·6
1056
1·9
136
0·56
1·19
13
24
0·5
0·01
1·2
7
0·1
0·5
0·08
0·04
34
3162
5·3
2·9
0·45
25·5
1160
1·4
136
0·37
1·01
4
25
0·2
0·5
0·02
2·8
8
0·0
2
0·04
0·07
4
76
2502
7·9
2·7
0·38
27·0
1175
2·4
140
0·40
1·16
8
30
0·2
0·4
0·02
0·3
7
0·0
1
0·04
0·06
4
66
3162
9·6
3·6
0·42
40·5
954
1·8
139
0·53
1·34
11
15
0·5
0·7
0·03
0·8
4
0·1
1
0·03
0·07
4
3
0·11
100·25
0·06
100·24
4
0·06
100·23
100·07
4
3
4
0·04
100·23
0·03
Al
100·34
0·12
100·25
100·24
4
3
3
0·04
63
2868
5·1
3·0
0·36
38·8
1086
2·1
143
0·58
1·12
15
9
0·2
0·6
0·01
0·6
7
0·0
1
0·04
0·03
83
3019
7·3
0·53
26·6
1101
1·7
130
0·58
0·91
14
45
0·9
0·04
3·0
11
0·2
0
0·10
0·05
95
2678
8·4
0·41
26·7
1146
3·9
139
0·39
0·99
8
36
0·2
0·09
0·1
8
0·1
2
0·02
0·03
73
2659
6·3
0·42
22·8
1067
3·4
128
0·29
1·29
14
21
0·4
0·03
1·5
5
0·1
1
0·04
0·09
111
2729
4·5
3·0
0·56
77·6
1425
1·6
204
0·54
1·04
13
15
0·2
0·5
0·05
1·1
3
0·1
1
0·05
0·10
72
2377
4·5
2·8
0·53
54·9
1450
1·7
172
0·84
0·58
14
26
0·6
0·3
0·11
4·5
17
0·1
4
0·38
0·05
100·22
0·07
100·13
3
0·06
100·48
0·09
0·004
0·0030
0·18
49·57
0·383
0·132
99·87
0·0002
0·06
0·001
0·0006
0·05
0·017
49·23
0·389
0·133
99·32
0·0002
0·03
0·002
0·0006
0·025
46·65
0·295
0·204
0·0007
0·11
0·003
0·0057
0·025
46·16
0·317
0·201
0·0004
0·08
0·001
0·0011
13·13
0·024
46·73
0·305
0·187
0·04
0·0002
0·03
0·001
0·0012
0·06
100·73
0·21
100·37
4
0·15
100·62
0·04
4
(continued)
2492
BATANOVA et al.
MELT TRANSPORT IN SSZ MANTLE
Table 3: Continued
Sample
n*
Fo
SiO2
CaO
FeO
CoO
MgO
NiO
MnO
Total
6 17/2
5
84·72
39·80
0·033
14·61
0·015
45·45
0·322
0·212
100·44
0·03
0·04
0·009
0·03
0·0092
0·02
0·007
0·0011
5
85·96
39·97
0·041
13·46
0·024
46·25
0·421
0·186
0·03
0·03
0·009
0·05
0·0003
0·05
0·006
0·0007
6 7
1
84·31
40·32
0·047
14·99
0·015
45·2
0·282
0·213
101·08
6 7
4
85·46
39·77
0·011
13·92
0·023
45·89
0·324
0·201
100·15
0·12
0·14
0·00
0·09
0·002
0·15
0·02
0·00
5
86·41
40·27
0·012
13·09
0·023
46·72
0·224
0·204
0·03
0·04
0·00
0·03
0·0004
0·04
0·00
0·00
2
85·36
40·08
0·031
14·02
0·024
45·87
0·238
0·216
0·22
0·10
0·00
0·20
0·001
0·15
0·01
0·00
5
86·04
39·96
0·007
13·44
0·021
46·47
0·226
0·207
0·04
0·03
0·00
0·03
0·001
0·05
0·00
0·00
87·05
39·93
0·014
12·52
0·022
47·20
0·316
0·179
0·04
0·04
0·00
0·04
0·0004
0·05
0·00
0·00
s
6 20/4
s
s
6 5
s
6 5
s
7 16/1o
s
7 14/2
s
5
ny
Ca
Ni
Ti
3
92
2866
16
133
58
1643
7·1
5
18
0·3
112
2448
23
24
Al
Cu
Zn
Mn
Sc
Co
V
Li
3·0
0·66
80·4
1336
1·3
200
0·52
0·93
0·4
0·06
0·9
4
0·0
4
0·02
0·15
4·4
0·52
34·8
1567
1·7
146
0·51
0·84
0·3
0·04
0·7
4
0·1
1
0·03
0·06
8·9
2·7
0·53
53·0
1433
1·7
172
0·47
0·82
4·8
1·1
0·00
12·2
72
0·2
2
0·16
0·02
0·06
100·36
0·12
0·20
100·56
0·06
100·50
0·03
100·33
3
0·07
100·18
0·08
3
*Number of olivine grains analysed by EPMA.
yNumber of olivine grains analysed by LA ICP-MS.
Oxides are in wt %; trace elements in ppm; s, standard error ¼ standard deviation of mean/ˇn.
narrow dunite vein (Fig. 2b) and from various pyroxenite
and zoned composite dunite^pyroxenite veins (Table 1).
Spinel peridotite
The positions of the samples relative to the dunite bodies
(S1) and pyroxenite veins (S2) are shown in Table 1. The
exposures usually are two-dimensional and it is not
always clear that veins do not exist beneath the sample
locations. The spinel peridotites are mainly clinopyroxene-bearing harzburgites or clinopyroxene-poor lherzolites, which display foliation and banding formed
by orthopyroxene-rich or -poor bands. Two types of banding are observed: well-defined and strongly contrasting
10^15 cm wide bands, and diffuse thicker (metre-wide)
bands. The harzburgites display a well-expressed lineation.
The foliation is less distinct in comparison with banding
and lineation. The rocks are usually coarse-grained and
show a variety of deformational textures: protogranular,
tabular equigranular (mosaic) with polygonal grain
boundaries or irregular porphyroclastic textures. Harzburgites with protogranular (coarse-grained) textures dominate: olivine grains are 4^6 mm, enstatite 3^4 mm, diopside
0·3^1·0 mm, chromian spinel varies from 0·3 to 2 mm;
the amount of neoblasts is less than 10^15%.
The deformation textures of the Voykar spinel peridotites have been analysed in detail by Savelieva et al.
(1980, 2008). All of the studied samples exhibit evidence
of deformation including: lattice preferred orientation
(LPO) of olivine, kink-bands in olivine, foliation and
alignment of elongated olivine and Cr-spinel grains, and a
lineation defined by large stretched enstatite and neoblasts
of pyroxenes and olivine. The degree of serpentinization
of the spinel peridotite varies from 0 to 20^30%, rarely
up to 50%. Peridotites with equigranular, polygonal textures are usually almost free of low-temperature alteration
(Fig. 3a). The modal composition of the spinel peridotites
is given in Table 1. The amount of clinopyroxene varies
from 1 to 6 vol. %. The morphology of the clinopyroxene
depends strongly on the position of the sample relative
to dunite (S1) and pyroxenite (S2) veins. Large grains of
clinopyroxene (up to 2^3 mm) are very rare and restricted
to a few samples of harzburgite. Most clinopyroxene
grains have been recrystallized and, as a rule, form neoblasts (Fig. 3a).
Harzburgite samples located in the contact zone of
dunite bodies (S1) or within dunite (relics of harzburgite)
contain 1^2 vol. % of clinopyroxene, which forms
small rim-like interstitial grains.
The amount of clinopyroxene in harzburgite adjacent
to S2 pyroxenite veins and zoned, composite, dunite^
pyroxenite veins is about 3^6 vol. %. Within the reaction
zone between the host harzburgite and the pyroxenite
veins the clinopyroxene occurs as interstitial, poikilitic
grains between olivines (Fig. 3b). This newly formed
clinopyroxene cements equigranular recrystallized olivine
grains and obviously formed after recrystallization.
2493
JOURNAL OF PETROLOGY
VOLUME 52
NUMBER 12
DECEMBER 2011
Table 4: Spinel major element compositions in Voykar mantle lithologies
Sample (pu):
211/1
215/7
6 10/2
6 13
6 16/2
6 54/1
6 39/2
6 25/1
6 12/2
9
11
13
3
13
15
13
25
6
SiO2
0·02
0·02
0·12
0·06
0·08
0·08
0·08
0·06
0·07
TiO2
0·08
0·07
0·07
0·03
0·03
0·06
0·04
0·06
0·13
Al2O3
34·22
41·62
41·42
43·05
38·32
44·63
32·51
41·80
27·87
Cr2O3
33·44
25·61
25·67
24·16
28·15
22·47
35·80
25·35
37·70
V2O3
0·24
0·16
0·16
0·16
0·21
0·15
0·16
0·14
0·21
FeO
15·78
14·23
14·50
13·20
14·86
13·57
15·92
13·88
18·35
4·34
n:
Fe2O3
1·88
2·10
2·44
2·29
3·18
1·99
1·68
2·26
MnO
0·22
0·18
0·17
0·16
0·18
0·16
0·21
0·17
0·26
MgO
13·89
15·60
15·64
16·45
14·97
16·39
13·74
15·92
11·77
NiO
0·12
0·16
0·16
0·19
0·16
0·20
0·09
0·17
0·09
ZnO
0·23
0·28
0·24
0·24
0·22
0·23
0·24
0·23
0·26
100·11
100·02
100·69
100·09
100·46
100·02
100·57
100·04
101·07
Total
Mg-no.
0·611
0·661
0·658
0·690
0·642
0·683
0·606
0·672
0·533
s
0·004
0·003
0·004
0·001
0·003
0·002
0·004
0·002
0·003
Cr/(Cr þ Al)
0·396
0·292
0·294
0·274
0·330
0·253
0·425
0·289
0·476
s
0·006
0·004
0·005
0·006
0·004
0·004
0·004
0·002
0·002
Fe3þ/Fetotal
0·097
0·117
0·132
0·135
0·162
0·116
0·087
0·128
0·175
0·007
0·002
0·002
0·003
s
FMQ
s
Sample (pu):
n:
0·004
0·002
0·003
0·003
0·002
0·83
0·63
0·39
0·40
0·06
0·66
1·06
0·56
0·42
0·06
0·04
0·04
0·09
0·03
0·05
0·04
0·02
0·02
7 59/10c
7 59/10d
6 24
6 35/2
7 15c6
7 15c5
7 15c4
7 15c3
7 15c2
10
4
4
5
5
4
5
5
4
0·10
SiO2
0·02
n.a.
0·03
0·07
0·04
0·06
0·06
0·08
TiO2
0·10
0·11
0·06
0·07
0·10
0·07
0·10
0·21
0·28
Al2O3
25·66
24·42
41·44
43·91
30·34
30·16
27·59
20·77
17·51
Cr2O3
40·25
41·74
25·61
23·33
37·95
37·85
39·77
43·96
47·58
V2O3
0·21
0·21
0·18
0·14
0·16
0·16
0·16
0·16
0·14
FeO
19·23
19·77
14·58
13·22
15·32
15·73
16·76
19·45
20·33
Fe2O3
3·37
3·37
2·84
2·78
2·29
2·49
3·16
5·26
5·22
MnO
0·30
0·30
0·18
0·16
0·22
0·23
0·25
0·32
0·34
MgO
10·71
10·29
15·53
16·67
13·96
13·63
12·78
10·32
9·55
NiO
0·08
0·07
0·19
0·22
0·10
0·10
0·09
0·08
0·06
ZnO
0·29
0·32
0·26
0·21
0·22
0·23
0·24
0·23
0·21
100·21
100·60
100·88
100·74
100·71
100·69
100·97
100·83
101·31
Total
Mg-no.
0·498
0·481
0·655
0·692
0·619
0·607
0·576
0·486
0·456
s
0·002
0·007
0·005
0·001
0·006
0·006
0·006
0·004
0·008
Cr/(Cr þ Al)
0·513
0·534
0·293
0·263
0·456
0·457
0·492
0·587
0·646
s
0·002
0·007
0·006
0·002
0·002
0·003
0·002
0·003
0·003
Fe3þ/Fetotal
0·136
0·133
0·149
0·159
0·118
0·125
0·145
0·196
0·188
s
0·001
0·005
0·007
0·004
0·003
0·001
0·003
0·005
0·006
FMQ
0·12
0·12
0·19
0·12
0·48
0·36
0·06
1·02
1·00
s
0·02
0·04
0·12
0·06
0·04
0·04
0·07
0·05
0·04
(continued)
2494
BATANOVA et al.
MELT TRANSPORT IN SSZ MANTLE
Table 4: Continued
Sample (pu):
7 15c1
6 39/1
6 38/1
6 37/1
6 41
7 13/1
6 35/1
215/4
06 21/1
4
16
4
5
5
5
4
7
11
SiO2
0·06
0·10
0·07
0·08
0·06
0·09
0·08
0·01
0·09
TiO2
0·26
0·17
0·19
0·17
0·26
0·12
0·31
0·08
0·21
Al2O3
16·68
30·84
25·01
34·77
20·55
19·57
29·41
38·92
13·79
Cr2O3
47·85
32·68
41·24
28·50
43·70
46·26
34·96
27·36
48·06
V2O3
0·14
0·16
0·15
0·14
0·16
0·12
0·14
0·17
0·19
FeO
20·65
15·49
17·39
16·84
19·42
20·12
16·55
14·07
23·45
n:
Fe2O3
5·60
6·89
3·81
5·71
5·82
3·84
4·96
3·45
7·50
MnO
0·35
0·22
0·27
0·28
0·31
0·43
0·30
0·20
0·39
MgO
9·17
13·95
12·05
13·28
10·34
9·55
13·03
15·45
6·99
NiO
0·07
0·19
0·09
0·15
0·09
0·05
0·13
0·14
0·06
ZnO
0·20
0·16
0·25
0·17
0·19
0·29
0·14
0·26
0·18
101·04
100·87
100·65
100·09
100·90
100·43
100·01
100·20
101·03
Total
Mg-no.
0·442
0·616
0·552
0·584
0·487
0·458
0·584
0·662
0·347
s
0·010
0·004
0·007
0·009
0·006
0·007
0·007
0·007
0·005
Cr/(Cr þ Al)
0·658
0·416
0·525
0·355
0·588
0·613
0·444
0·321
0·700
s
0·010
0·002
0·004
0·012
0·007
0·006
0·008
0·009
0·003
Fe3þ/Fetotal
0·196
0·284
0·164
0·234
0·212
0·146
0·212
0·180
0·224
s
0·003
0·007
0·008
0·005
0·004
0·002
0·002
0·012
0·002
FMQ
1·18
1·38
0·71
1·06
1·14
0·74
0·75
0·07
1·21
s
0·04
0·06
0·12
0·03
0·04
0·05
0·04
0·12
0·02
6 23/1
6 26/1
6 27/1
6 11/4
6 11/3c
6 11/3d
6 33/5
7 33/5
6 33/4
4
11
5
4
4
4
9
14
10
0·08
Sample (pu):
n:
SiO2
0·09
0·09
0·11
0·06
0·07
0·06
0·09
0·05
TiO2
0·22
0·27
0·28
0·12
0·09
0·22
0·10
0·07
0·10
Al2O3
13·76
15·32
15·29
35·76
35·62
25·62
35·90
42·16
30·73
Cr2O3
48·47
48·45
48·33
31·29
29·74
39·41
31·18
26·12
35·95
V2O3
0·17
0·15
0·18
0·19
0·16
0·19
0·14
0·12
0·21
FeO
21·29
17·85
18·95
16·00
16·43
19·46
15·47
12·99
17·61
3·14
Fe2O3
7·84
7·34
7·18
2·93
3·57
3·95
2·74
1·84
MnO
0·36
0·32
0·33
0·21
0·28
0·36
0·19
0·16
0·23
MgO
8·37
10·87
10·21
14·13
13·56
10·69
14·39
16·70
12·55
NiO
0·09
0·11
0·10
0·13
0·15
0·07
0·14
0·19
0·10
ZnO
0·20
0·13
0·18
0·26
0·19
0·19
0·31
0·20
0·25
100·97
100·99
101·14
101·08
99·86
100·22
100·76
100·62
101·06
Total
Mg-no.
0·412
0·521
0·490
0·612
0·595
0·495
0·624
0·696
0·560
s
0·009
0·004
0·006
0·007
0·001
0·007
0·002
0·003
0·001
Cr/(Cr þ Al)
0·703
0·679
0·680
0·370
0·359
0·508
0·368
0·294
0·440
s
0·001
0·008
0·004
0·008
0·007
0·005
0·003
0·002
0·002
Fe3þ/Fetotal
0·249
0·269
0·254
0·141
0·164
0·154
0·138
0·113
0·138
s
0·004
0·007
0·013
0·005
0·005
0·002
FMQ
1·63
1·66
1·47
0·16
0·14
0·28
0·12
0·78
0·10
s
0·07
0·07
0·10
0·09
0·08
0·06
0·04
0·05
0·01
0·003
0·003
0·001
(continued)
2495
JOURNAL OF PETROLOGY
VOLUME 52
NUMBER 12
DECEMBER 2011
Table 4: Continued
Sample (pu):
6 33/2
6 33/1
7 33/3
6 33/3
7 59/10b
7 59/10a
6 12/1
6 17/2
6 20/4
5
15
8
12
3
5
2
3
3
SiO2
0·07
0·08
0·15
0·08
0·02
0·09
0·09
0·11
TiO2
0·09
0·13
0·16
0·16
0·10
0·11
0·13
0·12
0·18
Al2O3
35·04
34·95
29·05
25·06
25·72
23·50
26·90
31·42
26·19
Cr2O3
31·59
31·37
36·26
38·99
40·69
42·18
34·24
29·82
30·61
V2O3
0·19
0·20
0·20
0·19
0·21
0·21
0·28
0·26
0·36
FeO
16·26
16·88
18·83
19·31
19·11
19·73
22·40
21·70
24·72
n:
n.a.
Fe2O3
3·08
3·04
4·20
5·76
3·38
3·39
7·24
6·90
9·75
MnO
0·22
0·22
0·27
0·29
0·29
0·31
0·30
0·28
0·35
MgO
13·84
13·44
11·72
10·89
10·88
10·10
8·98
9·82
7·12
NiO
0·15
0·12
0·10
0·10
0·08
0·07
0·13
0·17
0·17
ZnO
0·18
0·21
0·21
0·18
0·34
0·30
0·18
0·31
0·18
100·71
100·74
101·15
101·10
100·80
99·93
101·04
101·01
100·07
Total
Mg-no.
0·602
0·586
0·526
0·501
0·504
0·477
0·417
0·447
0·339
s
0·015
0·009
0·006
0·003
0·028
0·006
0·017
0·004
0·033
Cr/(Cr þ Al)
0·378
0·376
0·456
0·511
0·515
0·546
0·461
0·389
0·440
s
0·019
0·006
0·002
0·001
0·002
0·004
0·008
0·002
0·020
Fe3þ/Fetotal
0·145
0·139
0·167
0·212
0·138
0·134
0·225
0·223
0·263
s
0·005
0·004
0·003
0·002
0·006
0·003
0·009
0·007
0·010
FMQ
s
Sample (pu):
0·15
0·10
0·46
1·02
0·11
0·11
0·76
0·85
1·48
0·13
0·09
0·06
0·03
0·08
0·02
0·14
0·06
0·05
65
7 16/1o
7 31/1
n:
5
5
3
SiO2
0·08
0·03
TiO2
0·07
0·10
0·11
Al2O3
45·70
40·58
24·97
Cr2O3
18·75
24·41
41·00
V2O3
0·18
0·21
0·21
FeO
17·68
18·61
18·62
Fe2O3
3·24
3·25
3·50
MnO
0·27
0·23
0·33
MgO
13·74
12·76
11·02
NiO
0·15
0·11
0·08
ZnO
0·39
0·31
0·26
100·26
100·61
100·13
Total
0·02
Mg-no.
0·581
0·550
0·513
s
0·007
0·003
0·001
Cr/(Cr þ Al)
0·216
0·288
0·524
s
0·005
0·002
0·003
Fe3þ/Fetotal
0·141
0·136
0·144
s
0·007
0·004
0·010
FMQ
0·31
0·46
0·11
0·04
s
2496
BATANOVA et al.
MELT TRANSPORT IN SSZ MANTLE
Fig. 3. Photomicrographs of the mantle lithologies of the Voykar ophiolite showing the microstructures and textural relationships between
minerals in cross-polarized light. (a) Mosaic texture of spinel harzburgite with polygonal olivine grains; (b) poikilitic newly formed Cpx
enclosing polygonal olivine grains in a spinel harzburgite adjacent to a pyroxenite vein; (c) coarse-grained protogranular texture of dunite
with elongated olivine grains; (d) reaction relationships between olivine, orthopyroxene, Cpx and amphibole (Amf) in an amphibole-bearing
pyroxenite (pu07-33/1).
Magmatic amphibole (1^2 vol. %) in harzburgites
within the harzburgite^pyroxenite contact zones occurs as
small interstitial grains or thin rims (as wide as 200 mm)
around clinopyroxene. Thus spinel harzburgite in reaction
zones around pyroxenite veins is characterized by crystallization of new clinopyroxene as well as amphibole.
Dunite (S1)
Dunite is composed of olivine (97^99 vol. %) and
Cr-spinel (1^3 vol. %), and in some cases sulphides (less
than 1%). Irregularly distributed clinopyroxene and
orthopyroxene (up to 2%) are sometimes present. Small
grains of clinopyroxene, less than 0·3 mm length, are
usually associated with Cr-spinel. The samples vary
from coarse-grained to very coarse-grained (41 cm) and
are characterized by protogranular textures (Fig. 3c).
Cr-spinel is euhedral and sometimes forms chains. The
degree of serpentinization is about 20^50%.
Pyroxenite (S2)
These samples are veins of clinopyroxenite (diopsidite)
and olivine websterite (diopside^enstatite rock) that cut
large dunite bodies or surrounding harzburgite. The
modal composition and thickness of clinopyroxenite,
websterite and zoned composite dunite^pyroxenite veins
(Fig. 2d^f) are given in Table 1. Reactive relationships
between the surrounding harzburgite and the pyroxenite
veins are frequently observed (Fig. 2d). Most samples
2497
JOURNAL OF PETROLOGY
VOLUME 52
contain accessory amounts of Cr-spinel (or Cr-magnetite).
Small amounts of magmatic amphibole are observed in
almost all of the pyroxenites. Textures vary from coarse to
giant (45 cm) irregularly grained. Relics of olivine
replaced by orthopyroxene are found in most samples.
The relationship between orthopyroxene and clinopyroxene is also frequently reactive.
Zoned composite dunite^pyroxenite
veins (ZCV) of S2
Two veins of zoned composite dunite^pyroxenite within
host spinel peridotite were sampled and studied in detail
(Fig. 2e and f). Contact rims of olivine^Cr-spinel websterite separate the spinel harzburgite from the central parts
of the veins, which are composed predominantly of coarse
equigranular dunite or pyroxene-bearing dunite. All of
the rocks contain globules of Cu^Fe^Ni sulphide (up to
1vol. %) associated with Cr-spinel.
The zoned dunite pyroxenite vein shown in Fig. 2f is
about 40 cm thick and consists of coarse-grained dunite
that includes bands and schlieren of websterite. Thick
rims (5^7 cm) of websterite line the contact with the
surrounding harzburgite (Fig. 2f). This vein is in turn cut
by a vein of amphibole pyroxenite. Samples were taken
from the dunite (pu7 33/3, pu6 33/3), a pyroxenite band
within the dunite (pu6 33/1) and the pyroxenite rim adjacent to the surrounding harzburgite (pu6 33/2) (Table 1).
Harzburgite samples were taken 0 cm (pu6 33/4), 40 cm
(pu7 33/5) and 70 cm (pu6 33/5) away from contact with
the vein. The sample of the late vein of amphibole pyroxenite (pu7 33/1) contains up to 50% of magmatic amphibole
and shows evidence of a reaction relationship between
the minerals (olivine, orthopyroxene, clinopyroxene and
amphibole). The relics of olivine are partly replaced by
orthopyroxene. Orthopyroxene, in turn, is replaced by
clinopyroxene, which is rimmed by amphibole (Fig. 3d).
A N A LY T I C A L M E T H O D S
The major element and trace element concentrations
of the whole-rocks (Table 2) were determined using a
Phillips PW 1404 X-ray fluorescence spectrometer at the
Department of Earth Sciences, University of Mainz,
Germany.
Electron microprobe analysis (EPMA) of the minerals
was performed using a Jeol JXA 8200 SuperProbe at the
Max Planck Institute for Chemistry (Mainz, Germany).
The compositions of olivines were analysed at an accelerating voltage of 20 kV and a beam current of 300 nA, following a special procedure suggested by Sobolev et al. (2007)
that allows 20^30 ppm (2s error) precision and accuracy
for Ni, Ca, Mn, Al, Ti, Cr, and Co, and 0·02 mol % for
the forsterite component in olivine. For each sample 5^20
grains of olivine were analysed. The average values for
NUMBER 12
DECEMBER 2011
each sample together with the 1s standard error are
reported in Table 3.
The composition of Cr-spinel was measured at 20 kVand
a 80 nA beam current. The calibration of was made using
a synthetic oxide standard set (P&H Developments Ltd.,
Calibration Standards for Electron Probe Microanalysis,
Standard Block GEO) for all elements except Mn (on
rhodonite). Ferric iron in spinel was calculated assuming
perfect stoichiometry. Repeated measurements of the
chromite USNM 117075 (Jarosewich et al., 1980) standard
and spinel samples Bar 8601-10 and Dar 8502-2 whose
Fe3þ/Fetotal ratio had been measured by Mo«ssbauer
spectroscopy (Ionov & Wood, 1992) have shown that the
selected method provides Fe3þ/Fetotal ratios accurate to
within the measurement error (Supplementary Data Table
1, available for downloading at http://www.petrology.
oxfordjournals.org). The average values for each sample
and errors are given in Table 4.
The compositions of pyroxenes and amphibole were
measured using a routine method with an acceleration
potential of 20 kV and beam current of 20 nA
(Supplementary Data Table 2). International natural mineral standards from the Smithsonian Institution were used
(Jarosewich et al., 1980). The ZAF correction procedure
was applied for all minerals.
Trace element abundances in clinopyroxene and olivine
and some orthopyroxene grains were obtained using a
laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) system at the Max Planck Institute for
Chemistry (Mainz, Germany). This system includes a
NewWave, Merchantek UP213 UV Nd^YAG laser coupled
to a Finnigan-MAT Element-2 magnetic sector field
ICP-MS system. Samples were ablated using 60^90 mm
spots, a repetition rate of 10 Hz and laser energy of
6 J cm2 in a He atmosphere. The measurements were calibrated using the NIST SRM 612 and KL2-G reference
glasses (Jochum et al., 2000), and Ca as a reference element
for clinopyroxene and Si for olivine and orthopyroxene
(Supplementary Data Table 3). Typical external precision
is better than 4% (RSD) for most elements. For each
sample 3^5 grains of olivine (Table 3) and 5^15 grains
of clinopyroxene were analysed (Table 5).
R E S U LT S
Bulk-rock chemistry
Major and selected trace element data for the studied
samples are given in Table 2. The spinel peridotites have
refractory compositions comparable with the most
depleted abyssal peridotites (Fig. 4a and b); they are interpreted as residua after melt extraction. The concentrations
of Al2O3 and CaO vary in the range 0·7^1·6 wt % and
0·7^1·8 wt % respectively. The observed variations in
Al2O3, CaO and MgO concentrations in the spinel
harzburgites correlate with their modal compositions,
2498
BATANOVA et al.
MELT TRANSPORT IN SSZ MANTLE
Table 5: Trace element abundances in Cpx determined by LA-ICP-MS, in ppm
Sample (pu):
n:
Li
s
211/1
16
s
215/7
n.a.
s
6 10/2
10
n.a.
s
6 13
4
3·69
0·25
s
6 16/2
5
n.a.
s
6 54/1
11
10
n.a.
7
n.a.
Sc
71
1
71
1
72
1
74
1
73
1
66
Ti
484
7
613
9
884
27
422
9
256
4
761
s
6 39/2
3
n.a.
0·5
9
s
6 25/1
s
6 12/2
4
6·74
1·08
2·31
0·08
68
2
73
1
77
1
292
14
563
23
525
16
V
268
2
258
3
249
4
267
2
288
3
249
2
210
8
260
10
191
5
Mn
527
3
596
9
600
6
564
10
597
10
516
5
512
9
624
27
593
17
Co
Ni
17·8
335
0·2
2
20·0
363
0·3
19·6
6
0·2
308
19·7
3
0·6
367
20·3
9
0·5
384
17·3
8
331
0·4
20·2
4
379
1·2
25
20·3
350
1·9
23
18·2
315
0·4
6
Sr
0·96
0·03
4·51
0·25
6·25
0·16
0·86
0·03
3·89
0·07
0·23
0·01
5·17
0·39
7·41
0·38
4·88
0·18
Y
3·47
0·05
5·83
0·06
7·67
0·22
5·52
0·06
3·37
0·04
7·45
0·11
2·89
0·20
5·72
0·24
3·34
0·17
Zr
0·17
0·01
0·67
0·04
3·07
0·14
0·08
0·00
0·13
0·01
0·10
0·01
1·16
0·10
0·85
0·05
1·40
0·04
La
0·011 0·001
0·030 0·002
0·055
0·003
0·008
0·002
0·037
0·001
b.d.l.
0·037
0·003
0·036
0·002
0·014
0·002
Ce
0·037 0·002
0·127 0·006
0·293
0·010
0·025
0·002
0·114
0·003
0·008 0·001
0·162
0·019
0·136
0·011
0·074
0·009
Pr
0·006 0·001
0·025 0·002
0·072
0·006
0·003
0·0002
0·017
0·001
0·004 0·0002
0·028
0·004
0·030
0·005
0·020
0·003
Nd
0·051 0·003
0·153 0·010
0·543
0·024
0·031
0·004
0·072
0·003
0·030 0·002
0·173
0·023
0·204
0·021
0·183
0·017
Sm
0·047 0·004
0·088 0·017
0·287
0·022
0·069
0·008
0·034
0·007
0·090 0·011
0·067
0·012
0·113
0·012
0·124
0·015
Eu
0·023 0·002
0·035 0·004
0·132
0·006
0·024
0·002
0·013
0·002
0·053 0·002
0·038
0·004
0·052
0·003
0·047
0·003
Gd
0·191 0·011
0·287 0·017
0·666
0·039
0·222
0·009
0·117
0·005
0·421 0·012
0·177
0·015
0·317
0·021
0·260
0·020
Tb
0·053 0·001
0·078 0·002
0·148
0·005
0·075
0·004
0·035
0·002
0·117 0·002
0·044
0·005
0·082
0·003
0·060
0·003
Dy
0·530 0·009
0·789 0·018
1·242
0·043
0·764
0·013
0·416
0·008
1·096 0·019
0·409
0·033
0·831
0·026
0·519
0·031
Ho
0·135 0·002
0·219 0·005
0·297
0·006
0·211
0·005
0·121
0·003
0·279 0·004
0·112
0·008
0·212
0·013
0·128
0·006
Er
0·455 0·005
0·738 0·022
0·917
0·018
0·734
0·010
0·453
0·016
0·929 0·016
0·374
0·020
0·733
0·020
0·445
0·017
Tm
0·075 0·002
0·109 0·005
0·134
0·004
0·115
0·004
0·071
0·002
0·148 0·004
0·063
0·007
0·115
0·005
0·071
0·003
Yb
0·527 0·009
0·815 0·017
0·933
0·030
0·800
0·023
0·567
0·011
1·018 0·014
0·472
0·021
0·822
0·068
0·530
0·018
Lu
0·081 0·002
0·124 0·003
0·139
0·004
0·117
0·005
0·087
0·002
0·156 0·003
0·075
0·004
0·125
0·008
0·074
0·003
Hf
0·019 0·001
0·052 0·004
0·104
0·005
b.d.l.
0·035 0·001
0·035
0·005
0·027
0·001
0·093
0·003
7 15C3
s
7 15c2
s
7 15c1
s
s
Sample (pu): 759/10c
n:
Li
3
8·07
s
6 24
4
1·53
3·52
s
6 35/2
4
0·26
2·41
b.d.l.
s
7 15C6
0·07
3·35
s
7 15C5
4
4
0·24
4·54
s
7 15C4
5
0·40
2·88
4
0·26
2·01
4
0·28
2·15
4
0·25
2·09
0·16
Sc
59
2
68
1
72
1
64
1
71
2
78
3
86
4
94
4
85
3
Ti
343
11
564
28
1309
75
470
13
309
9
433
9
589
15
537
34
557
5
V
165
2
284
4
267
5
195
3
197
3
175
5
144
3
115
8
106
2
Mn
646
24
531
4
460
14
507
19
528
9
478
13
410
16
446
13
436
3
Co
Ni
21·2
368
1·4
15
19·1
353
0·5
7
16·3
311
0·4
9
17·8
325
1·0
16
18·4
321
0·4
6
17·5
295
0·4
11
15·7
266
0·1
3
14·8
255
0·4
8
14·1
241
0·1
6
Sr
5·19
0·25
3·50
0·13
2·42
0·20
6·11
0·48
7·46
0·18
8·13
0·45
11·34
0·56
10·29
0·99
11·21
Y
3·30
0·25
5·96
0·22
5·73
0·51
3·44
0·10
3·54
0·10
3·88
0·29
4·72
0·06
3·26
0·29
3·33
0·55
0·15
Zr
0·75
0·06
2·00
0·13
1·54
0·06
4·00
0·19
1·73
0·08
3·08
0·21
4·95
0·05
3·50
0·50
4·02
0·09
La
0·022
0·002
0·044
0·004
0·007
0·001
0·073
0·004
0·075 0·004
0·068
0·006
0·108
0·007
0·065
0·011
0·061 0·003
Ce
0·116
0·010
0·218
0·014
0·056
0·007
0·354
0·024
0·309 0·001
0·281
0·022
0·417
0·020
0·263
0·037
0·255 0·005
Pr
0·031
0·003
0·053
0·002
0·022
0·003
0·082
0·007
0·056 0·004
0·054
0·004
0·075
0·003
0·048
0·006
0·044 0·002
Nd
0·240
0·011
0·397
0·015
0·197
0·016
0·532
0·043
0·352 0·011
0·373
0·029
0·455
0·024
0·258
0·030
0·280 0·017
(continued)
2499
JOURNAL OF PETROLOGY
VOLUME 52
NUMBER 12
DECEMBER 2011
Table 5: Continued
s
Sample (pu): 759/10c
s
6 24
3
n:
s
6 35/2
4
s
7 15C6
4
s
7 15C5
4
7 15C4
4
s
s
7 15C3
5
s
7 15c2
4
s
7 15c1
4
4
Sm
0·151
0·015
0·189
0·011
0·188
0·010
0·239
0·020
0·179 0·010
0·175
0·023
0·195
0·008
0·123
0·007
Eu
0·058
0·003
0·084
0·003
0·073
0·007
0·087
0·006
0·064 0·010
0·065
0·005
0·076
0·004
0·050
0·004
0·036 0·003
Gd
0·294
0·007
0·403
0·024
0·467
0·038
0·428
0·023
0·342 0·015
0·354
0·033
0·369
0·023
0·221
0·036
0·234 0·012
Tb
0·064
0·001
0·094
0·004
0·109
0·010
0·087
0·004
0·069 0·004
0·076
0·006
0·077
0·002
0·046
0·006
0·050 0·002
Dy
0·516
0·041
0·865
0·036
0·921
0·065
0·605
0·034
0·570 0·026
0·612
0·054
0·683
0·017
0·435
0·053
0·431 0·020
Ho
0·121
0·012
0·222
0·008
0·224
0·018
0·126
0·002
0·127 0·003
0·145
0·009
0·165
0·003
0·123
0·010
0·123 0·006
Er
0·401
0·031
0·746
0·028
0·724
0·060
0·372
0·009
0·406 0·020
0·486
0·025
0·626
0·015
0·434
0·045
0·428 0·034
Tm
0·057
0·006
0·114
0·004
0·110
0·008
0·055
0·002
0·063 0·002
0·070
0·004
0·099
0·002
0·074
0·007
0·073 0·003
Yb
0·418
0·027
0·834
0·039
0·798
0·058
0·361
0·014
0·430 0·011
0·507
0·028
0·687
0·064
0·575
0·046
0·533 0·025
Lu
0·057
0·005
0·126
0·005
0·119
0·010
0·053
0·001
0·066 0·002
0·076
0·006
0·104
0·002
0·087
0·008
0·079 0·006
Hf
0·050
0·001
0·056
0·006
0·115
0·002
0·153
0·008
0·058 0·002
0·105
0·007
0·198
0·013
0·187
0·022
0·212 0·006
s
Sample (pu): 6 39/1 6 38/1
n:
Li
1
n.a.
4
s
6 37/1
2
n.a.
s
6 41
7
n.a.
s
7 13/1
2
n.a.
3·61
s
6 35/1
3
0·19
s
215/4
10
n.a.
s
6 11/4
4
n.a.
2·85
0·135 0·012
s
6 11/3c
4
0·34
7 33/1
1
n.a.
2·04
Sc
115
107
1
113
3
91
3
89
1
115
5
66
1
74
2
64
Ti
611
929
24
1136
97
595
13
378
5
1509
103
1102
18
795
26
773
12
V
148
163
3
236
7
147
4
132
1
238
14
277
3
249
4
241
3
244
Mn
231
407
9
441
19
429
18
392
1
420
32
607
11
626
11
660
23
657
Co
Ni
15·0
267
14·9
302
0·4
7
18·7
281
0·04
6
17·5
296
0·4
5
14·0
287
0·4
16
16·3
272
0·2
6
20·0
424
0·6
9
19·6
333
1·1
9
22·6
367
0·3
1·5
10
68
699
18·3
390
Sr
6·08
7·14
0·13
2·96
0·04
7·57
0·15
1·18
0·00
13·15
1·19
6·16
0·11
4·39
0·09
7·28
0·10
Y
5·06
7·74
0·21
5·56
0·18
4·61
0·10
4·37
0·29
9·96
0·37
9·04
0·16
5·89
0·08
5·44
0·08
6·75
5·20
Zr
1·91
3·70
0·08
1·69
0·14
2·37
0·08
1·74
0·07
8·91
0·57
2·51
0·06
1·79
0·04
1·77
0·02
1·23
La
0·076
0·043
0·003
0·035
0·003
0·088
0·004
0·006
0·0002
0·105
0·005
0·076
0·002
0·036
0·003
0·048
0·002
0·054
Ce
0·289
0·180
0·012
0·138
0·009
0·313
0·010
0·034
0·002
0·501
0·010
0·325
0·007
0·176
0·005
0·196
0·055
0·240
Pr
0·060
0·037
0·001
0·030
0·003
0·049
0·002
0·009
0·001
0·124
0·001
0·072
0·002
0·048
0·0004
0·065
0·001
0·055
Nd
0·332
0·235
0·022
0·197
0·007
0·258
0·008
0·081
0·002
0·880
0·014
0·546
0·014
0·376
0·014
0·515
0·007
0·453
Sm
0·133
0·144
0·006
0·091
0·009
0·107
0·007
0·052
0·006
0·417
0·003
0·362
0·014
0·247
0·011
0·305
0·011
0·275
Eu
0·073
0·060
0·003
0·048
0·0001
0·047
0·002
0·029
0·005
0·172
0·012
0·165
0·005
0·105
0·006
0·138
0·005
0·100
Gd
0·331
0·356
0·013
0·259
0·003
0·242
0·008
0·150
0·019
0·839
0·004
0·865
0·027
0·508
0·017
0·617
0·016
0·548
Tb
0·076
0·096
0·003
0·065
0·002
0·062
0·002
0·045
0·003
0·191
0·0001
0·191
0·004
0·117
0·003
0·123
0·002
0·115
Dy
0·724
0·942
0·024
0·670
0·008
0·590
0·012
0·487
0·052
1·547
0·045
1·510
0·039
0·923
0·011
0·972
0·015
0·854
Ho
0·195
0·275
0·010
0·199
0·006
0·170
0·005
0·157
0·008
0·377
0·021
0·338
0·007
0·226
0·003
0·216
0·005
0·193
Er
0·708
1·023
0·024
0·784
0·023
0·614
0·012
0·606
0·014
1·314
0·038
1·051
0·030
0·704
0·012
0·624
0·012
0·611
Tm
0·103
0·176
0·007
0·138
0·006
0·096
0·003
0·103
0·0004
0·191
0·013
0·141
0·004
0·103
0·004
0·088
0·007
0·084
Yb
0·703
1·189
0·042
1·019
0·027
0·719
0·024
0·770
0·020
1·318
0·107
0·961
0·018
0·725
0·009
0·601
0·017
0·616
Lu
0·093
0·161
0·005
0·150
0·001
0·099
0·004
0·105
0·002
0·193
0·016
0·136
0·002
0·101
0·002
0·084
0·002
0·090
Hf
0·072
0·136
0·003
0·074
0·006
0·131
0·004
0·101
0·005
0·373
0·024
0·126
0·005
0·098
0·005
0·086
0·005
0·064
(continued)
2500
BATANOVA et al.
MELT TRANSPORT IN SSZ MANTLE
Table 5: Continued
s
Sample (pu): 6 11/3d
n:
Li
4
s
6 33/5
n.a.
n.a.
1
56
1
63
Ti
660
13
765
10
969
V
205
2
198
2
219
Mn
678
8
514
8
539
Ni
21·6
303
0·2
4
17·7
343
0·3
6
s
6 33/2
16
4·82
69
s
6 33/4
7
Sc
Co
s
7 33/5
4
s
6 33/1
10
4
n.a.
0·22
n.a.
63
1
66
1
69
1
70
1
84
2
57
1
10
413
6
792
12
843
19
678
11
442
8
370
12
2
211
3
258
3
263
4
236
2
181
4
150
7
13
631
7
683
15
688
13
665
7
465
12
603
21
0·8
21·3
9
0·4
356
22·5
6
0·9
409
2·15
s
7 59/10b
10
0·20
19·0
n.a.
s
6 33/3
10
0·2
328
n.a.
s
7 33/3
11
22·0
10
1·0
364
20·6
9
0·5
352
17·6
10
314
5·59
0·4
5
0·48
20·9
382
0·9
11
Sr
7·12
0·12
1·80
0·13
5·24
0·18
9·35
0·21
6·96
0·07
8·06
0·15
7·17
0·12
17·87
0·38
5·18
0·32
Y
4·96
0·07
4·17
0·15
8·38
0·16
3·87
0·06
6·04
0·09
6·20
0·15
5·00
0·09
4·36
0·11
3·17
0·16
Zr
1·53
0·05
6·84
0·13
0·86
0·08
1·08
0·02
1·61
0·03
1·40
0·05
1·16
0·03
2·26
0·06
0·75
0·06
La
0·043
0·002
0·008
0·001
0·021
0·001
0·055 0·002
0·056
0·001
0·048
0·002
0·052
0·002
0·113
0·004
0·020
0·001
Ce
0·225
0·002
0·043
0·002
0·093
0·002
0·237 0·005
0·273
0·004
0·237
0·008
0·230
0·006
0·433
0·012
0·113
0·009
Pr
0·054
0·003
0·017
0·001
0·022
0·001
0·052 0·001
0·066
0·001
0·063
0·003
0·053
0·001
0·082
0·003
0·029
0·003
Nd
0·460
0·009
0·230
0·022
0·161
0·010
0·338 0·009
0·502
0·011
0·497
0·014
0·411
0·008
0·527
0·017
0·231
0·018
Sm
0·281
0·005
0·258
0·038
0·162
0·004
0·179 0·009
0·312
0·008
0·308
0·013
0·244
0·006
0·185
0·016
0·134
0·008
Eu
0·110
0·006
0·120
0·009
0·083
0·004
0·070 0·002
0·126
0·004
0·138
0·007
0·097
0·002
0·083
0·004
0·065
0·005
Gd
0·514
0·021
0·532
0·027
0·556
0·016
0·343 0·011
0·623
0·015
0·661
0·024
0·507
0·013
0·366
0·017
0·296
0·022
Tb
0·110
0·002
0·103
0·008
0·143
0·003
0·071 0·002
0·125
0·003
0·144
0·004
0·107
0·002
0·079
0·003
0·061
0·003
Dy
0·843
0·025
0·753
0·049
1·271
0·024
0·620 0·013
1·003
0·021
1·099
0·032
0·848
0·016
0·637
0·019
0·512
0·013
Ho
0·199
0·004
0·156
0·008
0·317
0·005
0·149 0·004
0·231
0·005
0·244
0·008
0·198
0·003
0·163
0·007
0·118
0·006
Er
0·616
0·016
0·471
0·020
1·039
0·019
0·478 0·010
0·691
0·017
0·738
0·020
0·612
0·011
0·556
0·017
0·378
0·017
Tm
0·082
0·002
0·073
0·002
0·154
0·003
0·075 0·002
0·102
0·003
0·098
0·004
0·090
0·002
0·089
0·003
0·055
0·003
Yb
0·602
0·026
0·443
0·010
1·017
0·020
0·496 0·011
0·696
0·010
0·693
0·025
0·601
0·014
0·650
0·014
0·365
0·023
Lu
0·085
0·002
0·064
0·002
0·141
0·004
0·076 0·002
0·099
0·002
0·100
0·004
0·089
0·002
0·093
0·004
0·053
0·005
Hf
0·077
0·004
0·222
0·008
0·082
0·005
0·053 0·002
0·087
0·002
0·089
0·004
0·073
0·002
0·125
0·004
0·048
0·003
Sample (pu): 7 59/1a
n:
Li
s
4
4·66
15
0·40
n.a.
0·4
61
Sc
59
Ti
422
8
344
V
184
3
215
Mn
598
7
830
Co
Ni
20·5
386
s
214/7
1·4
7
30·6
327
s
6 12/1
10
10
n.a.
0·5
1
54
4
356
4
365
2
229
3
195
11
884
21
840
0·4
32·8
368
0·8
7
29·5
361
s
6 20/4
20
n.a.
62
3
s
6 17/2
9
n.a.
0·4
s
6 7
7 16/1o
s
4
n.a.
1·74
7 14/2
s
4
0·02
1·66
7 31/1
s
4
0·17
0·64
0·14
58
1
61
1
90
1
66
3
78
3
4
355
3
368
14
981
18
452
9
259
10
1
190
1
230
7
296
3
263
2
232
8
10
832
12
885
23
797
14
878
38
909
15
0·5
5
29·3
361
0·4
6
33·8
372
1·2
8
23·0
205
0·6
4
30·0
349
1·9
14
30·7
307
1·2
11
Sr
5·69
0·10
7·61
0·05
7·72
0·04
6·65
0·04
6·18
0·05
7·90
0·10
6·90
0·10
7·51
0·16
4·03
Y
3·23
0·11
2·74
0·03
2·73
0·06
2·60
0·05
2·48
0·04
2·85
0·06
7·48
0·27
3·25
0·13
1·80
0·13
0·06
Zr
0·92
0·04
0·56
0·01
0·57
0·02
0·50
0·02
0·41
0·01
0·65
0·04
2·16
0·04
0·71
0·05
0·34
0·02
La
0·027
0·001
0·021 0·001
0·022 0·001
0·024 0·001
0·020 0·001
0·023 0·001
0·045
0·002
0·033
0·002
0·011
0·001
Ce
0·146
0·005
0·109 0·001
0·120 0·003
0·120 0·003
0·102 0·001
0·125 0·003
0·256
0·005
0·158
0·005
0·059
0·003
Pr
0·037
0·002
0·029 0·001
0·032 0·001
0·033 0·001
0·027 0·001
0·030 0·001
0·072
0·003
0·039
0·002
0·014
0·0004
Nd
0·278
0·010
0·245 0·007
0·252 0·009
0·230 0·007
0·218 0·005
0·244 0·004
0·646
0·017
0·296
0·011
0·096
0·004
(continued)
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DECEMBER 2011
Table 5: Continued
Sample (pu): 7 59/1a
n:
4
Sm
0·170
Eu
0·068
Gd
s
214/7
s
6 12/1
s
6 17/2
s
6 20/4
s
67
s
s
s
s
20
0·010
0·160 0·007
0·146 0·012
0·113 0·012
0·126 0·004
0·151 0·009
0·427
0·003
0·173
0·007
0·066
0·005
0·062 0·002
0·062 0·003
0·056 0·003
0·055 0·002
0·065 0·003
0·179
0·006
0·075
0·003
0·029
0·003
0·338
0·010
0·283 0·008
0·297 0·007
0·276 0·015
0·253 0·005
0·296 0·007
0·849
0·033
0·348
0·013
0·147
0·010
Tb
0·070
0·002
0·056 0·002
0·057 0·002
0·055 0·002
0·052 0·001
0·062 0·001
0·172
0·006
0·070
0·001
0·034
0·001
Dy
0·537
0·024
0·449 0·008
0·463 0·014
0·430 0·015
0·415 0·008
0·475 0·012
1·285
0·040
0·534
0·021
0·319
0·010
Ho
0·125
0·005
0·105 0·001
0·106 0·002
0·105 0·003
0·097 0·002
0·110 0·003
0·292
0·005
0·127
0·009
0·074
0·006
Er
0·374
0·011
0·338 0·008
0·329 0·010
0·308 0·010
0·292 0·006
0·347 0·013
0·847
0·025
0·386
0·013
0·240
0·010
Tm
0·053
0·003
0·046 0·002
0·043 0·003
0·046 0·004
0·042 0·001
0·053 0·003
0·119
0·003
0·057
0·002
0·036
0·002
Yb
0·369
0·014
0·337 0·008
0·350 0·010
0·314 0·011
0·290 0·006
0·370 0·011
0·785
0·035
0·403
0·021
0·253
0·008
Lu
0·056
0·003
0·052 0·001
0·052 0·002
0·048 0·001
0·045 0·001
0·054 0·003
0·110
0·005
0·061
0·003
0·041
0·004
Hf
0·052
0·003
0·033 0·002
0·035 0·002
0·027 0·002
0·024 0·001
0·038 0·003
0·111
0·004
0·039
0·001
0·025
0·001
The Fo content [Fo ¼100 Mg/(Mg þ Fe2þ)] of olivine in
the harzburgites varies from 90·15 to 91·62 and depends
4
7 31/1
10
Major and trace element mineral
compositions
Olivine
4
7 14/2
10
particularly their orthopyroxene and clinopyroxene contents. The orthopyroxene-enriched band (pu07-59/10b)
plots on the low-MgO side. A sample of spinel peridotite
adjacent to the S2 composite dunite^pyroxenite veins has
higher CaO and Al2O3 contents than the harzburgites
located 40 and 70 cm from this vein. This sample contains
a significant amount of newly formed clinopyroxene
and could thus have been re-enriched during melt
infiltration.
Dunites formed during the early stage melt percolation
(S1) are distinguished from the late dunites (S2) in composite dunite^pyroxenite veins by their low concentrations
of CaO, which could be related to the higher modal
contents of clinopyroxene in the latter. Compared with
the surrounding spinel peridotites, the dunites of S1 and
S2 have lower SiO2, Al2O3 and CaO concentrations
(Al2O3 0·28^0·82 wt %, CaO 0·12^0·56 wt %) and a
higher MgO content (46·2^50·4 wt %) (Fig. 4a and b).
The small variations in the Al2O3 content of the dunites
reflect varying amounts of accessory Cr-spinel.
Pyroxenites have low concentrations of Al2O3, TiO2,
Na2O and K2O (1·4^3·3 wt %, 0·03^0·11wt %, 50·10 wt
% and 50·01wt %, respectively) (Table 2). Their CaO
and MgO contents reflect the modal proportion of clinoand orthopyroxene (Fig. 4c and d). An exception to this
trend is the pyroxenite (pu07-33/1), which contains 50%
magmatic amphibole (magnesiohornblende) and high
concentrations of all of the elements listed above.
9
7 16/1o
15
4
0·015
strongly on the position of the sample relative to the
dunite bodies and pyroxenite veins (Table 3). The Fo
content of olivines from harzburgite samples located far
from visible contacts with ‘melt pathways’ shows limited
variations from 90·41 to 91·23. The Fo content of olivine
increases in harzburgite samples adjacent to S1 dunites
(up to 91·42^91·62), whereas it decreases to 90·15^90·51 in
harzburgite adjacent to S2 pyroxenite and composite
dunite^pyroxenite veins (Fig. 5a and b).
Olivines from the S1 dunite show a wide range of Fo
contents (88·88^92·61). The majority of dunite samples
have higher Fo contents than those of the harzburgites
(Fig. 5a). The large dunite bodies are internally inhomogeneous in terms of the Fo content of olivine (88·88^
92·24). Low values of Fo in S1 dunite samples adjacent to
orthopyroxenite veins cross-cutting large dunite bodies
probably result from late-stage (S2) melt percolation
(Table 1).
The samples of S2 dunite in composite dunite^
pyroxenite veins are characterized by low Fo contents compared with the surrounding harzburgite and S1 dunite
(Tables 1 and 3; Fig. 5).
Olivine in the pyroxenite veins is divided into two
groups, one with high (90·10^90·60) and the other with
low (85^87) Fo contents. The olivines from websterite
veins, composite dunite^pyroxenite veins and a thin clinopyroxenite vein (sample pu07-59/10a) belong to the first
group. Olivine from most of the pyroxenite veins belongs
to the second group. The olivine of the second group plots
away from the olivine^spinel mantle array (OSMA)
defined by Arai (1994) (Fig. 5a). Olivine in these clinopyroxenites occurs only as relics in clinopyroxene. The Fo
content of the olivine relics varies from 1 to 2% Fo in a
single thin section (Tables 1 and 3).
2502
BATANOVA et al.
MELT TRANSPORT IN SSZ MANTLE
Fig. 4. Bulk-rock abundances of Al2O3 and CaO vs MgO in Voykar peridotites and pyroxenites; (a) and (b) refer to spinel peridotites and
dunites; (c) and (d) refer to pyroxenites. The data for abyssal peridotites (small circles) are from http://www.petdb.org/. The partial melting
trend shown is that for Mamonia spinel lherzolites (Batanova et al., 2008). PM, primitive mantle (Hofmann, 1988); Hz, spinel harzburgite; Hz
relic in Du of S1, relic of spinel harzburgite within dunite body; Hz adj. vein of S2, spinel harzburgite adjacent to pyroxenite and zoned
composite dunite^pyroxenite veins of late-stage (S2) melt percolation; Du of S1 and Du of S2, dunite formed during early (S1) and late (S2)
stages of melt percolation.
The concentrations of Ca and Ti in olivines from
harzburgites are close to the detection limit even of
high-precision EPMA, and Cr and Al concentrations are
below it (Table 3). For samples of different mantle lithologies with similar Fo contents, olivine from dunites has
relatively high Ca and Ti and low Al and Ni, and olivine
from pyroxenites has low Ca, Ti, and Al similar to that of
olivine from surrounding harzburgite (Table 3).
Olivines from Voykar lithologies define the two groups
distinguished by their Ni and Fo content (Fig. 6). Spinel
harzburgites, dunites and some pyroxenites contain olivines with high Fo contents similar to those in mid-ocean
ridge basalt (MORB); these are thought to form from
a dominantly peridotitic protolith (Sobolev et al., 2007).
Compared with the surrounding harzburgites, the Ni content of olivine tends to be low in dunites but higher in
some pyroxenites. The second group includes olivine with
relatively low Fo contents in pyroxenites. These plot
within the field of high-Ni olivines from within-plate
magmas formed under thick lithosphere (Sobolev et al.,
2007), and olivines from subduction-related calc-alkaline
series (Straub et al., 2008) (Fig. 6). These types of magmas
have been inferred to contain a large fraction of melt
derived from a hybrid pyroxenite source (Sobolev et al.,
2007; Straub et al., 2008).
Cr-spinel
The spinel Cr-number [ ¼ Cr/(Cr þAl)] of spinels in
harzburgite varies widely from 0·25 to 0·53 (Table 4).
These variations are consistent with those in olivine
(Fig. 5a and b) and depend upon the distance from the
contacts of S1 dunite and S2 pyroxenite veins. In samples
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far from contacts with ‘melt pathways’ Cr/(Cr þAl) is
0·25^0·29, corresponding to a moderately depleted abyssal
peridotite. Higher ratios in harzburgite adjacent to S1
dunite (up to 0·49) correlate positively with the Fo content
of olivine. Thus the Fo^spinel Cr-number values in
harzburgites near contacts with S1 bodies plot within the
intersection of highly refractory abyssal harzburgites and
SSZ peridotites (Fig. 5a). The olivine and spinel from harzburgite samples within the reaction zones of S2 pyroxenite
and composite dunite^pyroxenite veins define a second
trend in Fig. 5a and b in which spinel Cr-number shows
a negative correlation with Fo content.
The TiO2 content of spinel increases abruptly at the
transition from S1 harzburgite to S1 dunite and from S2
harzburgite to pyroxenite and correlates positively with
spinel Cr-number (Fig. 7a; Table 4).
Oxygen fugacities were calculated using the method of
Ballhaus et al. (1991) for P ¼1·4 GPa,T ¼10008C (estimated
below). The results are given in Tables 1 and 4, quoted as
log units relative to the fayalite^magnetite^quartz (FMQ)
buffer. Spinel harzburgites have log fO2(FMQ) from
1·06 to þ0·42 and plot below the boundary of MOR
harzburgites and SSZ harzburgites (Dare et al., 2009)
(Fig. 7b). However, oxygen fugacities are higher in
harzburgite samples located within the reaction zones of
S1 and S2 ‘magmatic bodies’, shifting their composition
toward the field of SSZ peridotites. Compared with
harzburgites, S1 dunites and S2 websterites and dunites
exhibit higher oxygen fugacities [up to þ1·7 log
fO2(FMQ)] typical of SSZ harzburgites and dunites
(Parkinson & Pearce, 1998; Parkinson & Arculus, 1999;
Pearce et al., 2000) (Fig 7b). The oxygen fugacities of
all samples increase as spinel Cr-number increases.
Orthopyroxene
Orthopyroxene compositions are presented in Supplementary Data Table 3 and are not discussed further here.
Clinopyroxene
Fig. 5. Variation of spinel Cr-number vs olivine Fo (mol %) for the
Voykar mantle lithologies (spinel peridotites, dunites and pyroxenites): (a) relative to the fields of abyssal peridotites (after Dick, 1989;
Johnson & Dick, 1992; Hellebrand et al., 2001; Seyler et al., 2003,
2007), SSZ peridotites (after Parkinson & Pearce, 1998; Pearce et al.,
2000), the olivine^spinel mantle array (OSMA) of Arai (1994), and
a partial melting trend based on experimental data obtained at
15 kbar by Jaques & Green (1980); (b) the variation across a transect
through an S1 dunite vein (Fig. 2b) and zoned composite dunite^
pyroxenite S2 veins (Fig. 2e and f). The arrows show the direction of
the compositional changes in the harzburgites adjacent to the S1
dunite, and pyroxenite S2 and composite dunite^pyroxenite vein
ZCV respectively. Other symbols are the same as in Fig. 4.
Clinopyroxene (Cpx) is found in all Voykar lithologies
except for some S1 dunites. Major and trace element compositions are reported in Supplementary Data Table 2 and
Table 5 respectively. The pyroxene is a Cr-diopside with
low Na2O and TiO2 concentrations. Al2O3 contents of
Cpx from harzburgites, S1 and S2 dunites and pyroxenites
vary in the same range (1·5^3·9 wt %), whereas the
Mg-numbers of Cpx in the pyroxenites are usually
lower (88·8^93·3) than in the harzburgites and S1 dunites
(93·3^95·5) (Supplementary Data Table 2).
The trace element patterns of clinopyroxene from
harzburgites (Fig. 8a and b) are characterized by a wide
range of variation in light rare earth elements (LREE)
and a more restricted range in the heavy REE (HREE).
The REE concentrations of Cpx from harzburgite are
within the field for abyssal peridotites, but at the same
2504
BATANOVA et al.
MELT TRANSPORT IN SSZ MANTLE
Fig. 6. Variation of NiO wt % in olivine vs Fo (mol %) for the Voykar mantle lithologies. The fields of olivines from MORB and within-plate
magmas formed under thick lithosphere (WPM-thick) are from Sobolev et al. (2005); the data for olivines of SSZ-related calc-alkaline volcanics
are from the calc-alkaline Popocatepetl volcano, Mexican volcanic belt (Straub et al., 2008). The black diamonds are NiO compositions corrected for subsolidus re-equilibration (see discussion).
contents of HREE, they are relatively enriched in
LREE (Fig. 8a^d). Clinopyroxene in sample pu06-54/1 is
exceptional in being similar to Cpx from abyssal
peridotites for HREE, but having lower middle REE
(MREE). We consider this sample as the least affected by
melt percolation processes. Cpx from all harzburgite
samples exhibits positive Sr anomalies that are typical
features for pyroxenes from SSZ peridotites (Parkinson &
Pearce, 1998).
The Cpx of harzburgites adjacent to contacts with veins
shows strong LREE enrichment and relative depletion in
HREE, compared with Cpx from abyssal peridotites. Its
trace element patterns are similar to those of Cpx from
the pyroxenite veins (Fig. 8e and f). The variations in
incompatible elements in Cpx across the margins of S2
pyroxenite veins (Fig. 2e and f) are shown in Fig. 9a^f.
From these figures it is obvious that the trace elements in
Cpx of the harzburgites must have re-equilibrated with
the percolating melt or fluid that formed the pyroxenite
veins. The degree of re-equilibration increases towards the
contact of each vein. In the narrow reaction zone directly
at the contacts the newly formed Cpx has the same trace
element pattern as the pyroxenite veins Cpx (Fig. 9).
This Cpx displays strong enrichment in LREE, Sr and Zr,
and depletion in HREE, compared with the Cpx in harzburgite sample pu06-54/1, which we regard as the least
affected by melt percolation processes.
The trace element patterns of Cpx in the S1 dunites are
highly variable (Fig. 10a and b) and do not depend on the
size of the bodies. The LREE, Sr and MREE contents are
similar to those of Cpx from the S2 pyroxenite veins.
Because the dunite Cpx grains are characterized by
positive Hf anomalies, negative Zr anomalies are not
pronounced. The Cpx of some S1 dunites contains lower
LREE abundances than Cpx from the S2 pyroxenites and
dunites. Compared with Cpx from the host harzburgites,
the HREE abundances in Cpx from the S1 dunites have
similar or higher concentrations. This feature has also
been observed in Cpx from dunites in other ophiolites
(Suhr et al., 2003) and is in remarkable contrast to the
Cr-number of spinel and Fo of olivine, which are both
higher in the dunites than in the surrounding harzburgites.
The trace element contents of Cpx from the S1 dunite
pu06-35/1 (Fig. 10a and b) are markedly different from
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JOURNAL OF PETROLOGY
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DECEMBER 2011
Fig. 7. (a) Variation of Cr/(Cr þAl) vs TiO2 wt % and (b) log fO2 vs Cr/(Cr þAl) for spinel from the various lithologies of the Voykar
mantle section. The field for abyssal peridotites is after Bryndzia & Wood (1990); that for SSZ peridotites is after Parkinson & Pearce (1998),
Parkinson & Arculus (1999) and Pearce et al. (2000); the boundaries between mid-ocean ridge (MOR) and SSZ harzburgites and dunites are
from Dare et al. (2009). The black arrows show the compositional changes of spinel and the variation of log fO2 along the harzburgite^
dunite vein transect shown in Fig. 2b.
2506
BATANOVA et al.
MELT TRANSPORT IN SSZ MANTLE
Fig. 8. Chondrite-normalized trace element and REE patterns of clinopyroxenes from the Voykar harzburgite. (a, b) Cpx from harzburgites
compared with those from the Voykar pyroxenite veins and abyssal peridotite field (after Johnson et al., 1990; Johnson & Dick, 1992;
Hellebrand et al., 2001) as well as the single Cpx measurements that are close in HREE abundance to those from the Voykar harzburgites.
(c, d) Cpx from harzburgites located far away from dunite and pyroxenite veins. The sample pu06-54/1 with the highest HREE and the lowest
LREE is labelled. (e, f) Cpx from harzburgites adjacent to pyroxenite and dunite veins (contact zones). Chondrite normalization values
are from Anders & Grevesse (1989).
both Cpx in the surrounding peridotite and Cpx in the S2
pyroxenite veins. The variations of incompatible elements
in Cpx across dunite^harzburgite transitions (Fig. 2b) are
shown in Fig. 11.
The trace element patterns of clinopyroxene from
different pyroxenite veins (Fig. 10c and d) are remarkably
parallel to each other and differ only in their concentrations:
YbN varies from 1·6 to 4·9 and LaN from 0·05 to 0·24. All
patterns are characterized by positive Sr and negative Zr,
Hf and Ti anomalies. These patterns are similar to those
of Cpx phenocrysts from sample of high-Ca boninites
from the Troodos ophiolite upper pillow lavas (trds 5-36)
(Supplementary Data Table 6) but show even higher Sr
concentrations (see also Belousov et al., 2009).
Thus, the Cpx patterns of all harzburgite samples
indicate the influence of melt percolation. There is only a
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JOURNAL OF PETROLOGY
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DECEMBER 2011
Fig. 9. Chondrite-normalized trace element and REE patterns of clinopyroxene from samples collected across the following transects: (a, b) the
zoned composite dunite^pyroxenite vein (ZCV) and the surrounding harzburgite shown in Fig. 2f; (c, d) the composite dunite^pyroxenite
vein and the surrounding harzburgite shown in Fig. 2e; (e, f) the pyroxenite vein and adjacent harzburgite (samples pu06 12/1, pu06 12/2); the
vertical arrow in (f) shows the trend of changes in the composition of the Cpx in harzburgite as a result of interaction with melt. The Cpx
from the harzburgite sample pu06-54/1 regarded as the least affected by the melt percolation processes is highlighted. (a, b) sample position
shown in Fig. 2f: harzburgite 70 cm from contact with zoned composite dunite^pyroxenite vein (ZCV) is sample pu06 33/5; harzburgite 40 cm
from contact is sample pu07 33/5; harzburgite adjacent to vein is sample pu06 33/4; samples within vein: websterite, pu06-33/1 and 33/2; dunite,
pu06 33/3 and pu07 33/3. (c, d) sample position shown in Fig. 2e: harzburgite adjacent to vein is pu06-11/4; websterite vein rim is pu06/11c;
dunite adjacent to pyroxenite rim is pu06 11/3 cd; dunite vein center is pu06 11/3d.
slight difference between the Cpx patterns of harzburgites
that are far from contacts with pyroxenite and those in
the contact zones. Cpx from harzburgites remote from
contacts is characterized by higher HREE, a wider range
of LREE and more fractionated LREE/HREE ratios
compared with Cpx of harzburgites near vein contacts
(Fig. 8c and d). The Cpx grains from the majority of
samples of S1 dunite have trace element patterns similar
to those of Cpx from S2 pyroxenites, suggesting that the
S1 dunites were influenced by late-stage melts.
2508
BATANOVA et al.
MELT TRANSPORT IN SSZ MANTLE
Fig. 10. Chondrite-normalized trace element and REE patterns of clinopyroxene from the Voykar mantle dunites and pyroxenites. (a, b) Cpx
grains from large dunite bodies and small dunite veins compared with those from pyroxenites and harzburgites. The normal (N)-MORB Cpx
pattern is calculated using an average N-MORB (Kelemen et al., 2003) and Cpx/melt distribution coefficients from Hart & Dunn (1993).
(c, d) Cpx from pyroxenite veins compared with Cpx phenocrysts in boninites from Troodos upper pillow lavas (UPLIII; Sobolev et al., 1996;
Buchl et al., 2002).
Amphibole
Amphiboles occur in all the mantle lithologies of the
Voykar complex, most commonly close to contacts with
pyroxenite veins. They are ubiquitous in pyroxenites, but
rarely observed in harzburgites and dunites. Several generations of amphiboles are usually present within a single
sample of pyroxenite. The earliest amphibole has high Al
(Al2O3 10^12 wt %) and Cr (Cr2O3 41wt %) and low Ti
(TiO2 50·50 wt %), and is a magnesiohornblende according to the Leake et al. (2003) classification. The later generation of amphiboles gradually change in composition
towards low Al and high Si contents. Amphiboles from
harzburgites and dunites show the same compositional features as those from pyroxenites but have higher
Mg-number (91^93) and correspond to tschermakite and
magnesiohornblende. The trace element compositions
of representative amphiboles are shown in Fig. 12.
Amphiboles from the pyroxenites are strongly enriched in
large ion lithophile elements (LILE) such as Rb, Ba and
Sr compared with the high field strength elements
(HFSE) Nb and Zr. The majority of the amphiboles have
pronounced positive Pb anomalies relative to La and Ce.
The trace element patterns of amphibole and Cpx from
the same sample are parallel to each other, but concentrations in the amphibole are 3^5 times higher than those
in the Cpx (Belousov et al., 2009).
DISCUSSION
The structural relations and compositional features of the
Voykar mantle section allow distinction of two stages of
melt migration that significantly modified the composition
of the host peridotites. To understand the nature and
mechanisms of melt^rock interactions in the studied
peridotites, it is first necessary to recognize their original
petrological and geochemical characteristics before they
were affected by melt percolation.
Spinel harzburgites: melting and melt
migration
The compositional heterogeneities within the spinel harzburgites clearly demonstrate that two processesçpartial
2509
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VOLUME 52
NUMBER 12
DECEMBER 2011
Fig. 11. Chondrite-normalized trace element (a) and REE patterns (b) of clinopyroxenes from samples collected across dunite veins and
the surrounding harzburgite (see Fig. 2b). The field of Cpx from the Voykar pyroxenite veins is shown for comparison in (a). Sample position
(Fig. 2b): harzburgite 20 cm from dunite is pu07 15C6, harzburgite 5 cm from dunite is pu07 15C5, harzburgite adjacent to dunite is pu07
15C4; samples within dunite vein: dunite 3 cm from harzburgite is pu07 15C3, dunite 10 cm from harzburgite is pu07 15C2, dunite 15 cm from
harzburgite is pu07 15C1.
melting and melt migrationçwere involved in their formation. Harzburgites sampled far from the contacts with
dunite bodies and pyroxenite veins show narrow compositional ranges in the bulk-rocks, olivine and Cr-spinel,
and plot in the compositional field of abyssal peridotites
(Figs 4a, b and 5a). In addition, the oxygen fugacity
during the formation of these harzburgites corresponds to
that of abyssal peridotites (Fig. 7b). This suggests an initial
origin of the harzburgites by partial melting at an oceanic
spreading centre. The conditions of such melting are
estimated in the next section.
The mineral composition of harzburgites adjacent to
contacts with veins, corresponding to the S1 and S2 stages
of melt percolation, as well as the trace element compositions of Cpx in the majority of the harzburgite samples,
however, show evidence for later re-equilibration with
percolating melts (Figs 5, 7, 8 and 9). It is difficult to
estimate specifically the influence of the early stage of
melt percolation (related to dunite formation) on the
trace element composition of harzburgite Cpx, because
the dunites themselves were probably modified by
late-stage melts. However, the study of Cpx compositions
along the profile from host harzburgite into S2 veins
(Fig. 9) clearly indicates the influence of late-stage melt
percolation on the composition of Cpx. The Cpx grains
from harzburgites adjacent to the contact with zoned composite dunite^pyroxenite veins and pyroxenite veins have
trace element patterns that correspond nearly exactly to
that in the pyroxenites (Fig. 9). This indicates that the Cpx
in the harzburgites is almost completely re-equilibrated
with the melts that produced the pyroxenite veins. As a
consequence of its modification by melt, the harzburgite
Cpx becomes richer in LREE, MREE, Zr and Sr, and
poorer in HREE (Fig. 9e and f). The change in composition of the Cpx in harzburgites adjacent to pyroxenite
veins is associated with an increase in the modal amount
of Cpx as a result of the precipitation of newly formed
Cpx grains from the migrating melts. Hence, the modification of harzburgite Cpx composition near contacts with
the S2 pyroxenite veins is not related to an increase in
the degree of melting of the peridotite but rather reflects
the geochemical features of the percolating melts.
Partial melting modelling
The degree of partial melting of the original spinel
harzburgite can be estimated by simulating the melting
process using the REE composition of Cpx (e.g. Johnson
et al., 1990). Such modelling is relevant only for peridotites
that were not modified by later refertilization by percolating melts (see below). Among the studied harzburgites,
only sample pu06 54/1 contains Cpx that is strongly
depleted in LREE and Sr compared with HREEçthe
features expected for near-fractional melting under a
mid-ocean ridge (e.g. Johnson et al., 1990). Because the
LREE and Sr concentrations of peridotite and hence its
Cpx are expected to increase during reaction with melt,
the low amounts in Cpx in harzburgite pu06 54/1 indicate
that it has undergone only a low degree of refertilization
by percolating melts. The clinopyroxene of pu06 54/1 can
thus be regarded as a residual phase after partial melting
2510
BATANOVA et al.
MELT TRANSPORT IN SSZ MANTLE
Fig. 12. Primitive mantle (PM)-normalized trace element patterns of the amphiboles from pyroxenite veins and the surrounding harzburgite.
Amph in Hz and Amph in Pxt denote amphibole in harzburgite and pyroxenite, respectively. The normalizing values are from Hofmann (1988).
and its trace element composition can be used to evaluate
the extent of melt extraction and the conditions of partial
melting.
The Qpx from sample pu06 54/1 has a very low MREE/
HREE ratio similar to that reported for some clinopyroxenes in abyssal peridotites by Johnson et al. (1990),
Hellebrand et al. (2002a) and Brunelli et al. (2006).
As shown by those workers, the REE patterns of such
clinopyroxenes provide evidence that melting started
within the garnet stability field and then continued in the
spinel stability field. We conducted our simulations of
near-fractional melting modelling with the equation
developed by Sobolev & Shimizu (1992). The input
parameters (initial and melt modes, source composition,
and the melt/peridotite partition coefficients) are listed in
Supplementary Data Table 4. The best-fit data for MREE
and HREE, Zr, Ti, and Y of the clinopyroxene in sample
pu06-54/1 are shown in Fig. 13 and correspond to 6%
near-fractional melting in the garnet stability field and
8^10% near-fractional melting in the spinel stability field,
with a low residual porosity (0·1%). Thus, the total degree
of partial melting for the Voykar peridotites could be as
high as 16%. This result is consistent with their whole-rock
and mineral chemistries. It should be noted, however, that
the concentrations of Nd and Ce in peridotite pu06-54/1
Cpx are somewhat higher than predicted by the model.
This might be the result of underestimated residual
porosity in the model or of later small modification by
percolating melts.
Were the mantle peridotites subsequently re-melted in a
supra-subduction zone environment? Although this process
could have taken place, the degree of melting at that stage
was not significant, judging from the geochemistry of the
peridotites. More specifically, the HREE concentrations
of the Cpx in the harzburgites and the Cr-number of
spinel, at distances of more than 40 cm from the veins,
are similar to those for unaffected harzburgite pu06-54
(Table 1; Fig. 9a and b). Because these parameters are sensitive to the extent of melting (e.g. Dick & Bullen, 1984;
Johnson et al., 1990), we propose that its degree did not
exceed 1^3%.
P^T conditions estimates for the Voykar
mantle section
It is reasonable to assume that any information about the
primary P^T conditions of the Voykar mantle section was
overprinted during late-stage melt percolation events and
subsequent cooling. Consequently, we can only estimate
the P^Tconditions of the later events.
The pressure of the late-stage (S2) melt percolation
processes can only be evaluated indirectly, based on the
fact that all mantle lithologies affected by this process
(harzburgite, dunite and pyroxenite) contain small
amounts of a high-Al amphibole (magnesiohornblende).
Experimental data indicate that the amphibole stability
field in mantle peridotite is fairly narrow (Grove et al.,
2006), and that amphiboles are stable in association
2511
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NUMBER 12
DECEMBER 2011
Fig. 13. Chondrite-normalized REE patterns showing the results of the polybaric near-fractional melting modelling in the garnet followed by
the spinel stability field. The dotted and dashed lines show the predicted compositions of the residual Cpx produced by near-fractional melting
in the garnet (Ga) and spinel (Spl) stability fields. Percentages refer to the degree of melting in each field. Data for pu06 54/1 are shown
for comparison.
with olivine, pyroxenes and spinel at temperatures of
850^10508C and pressures of 0·8^1·7 GPa. The absence of
plagioclase in the studied Voykar mantle lithologies,
despite the fact that most of the pyroxenites are
plagioclase-normative, allows us to further constrain the
pressure within the range of 1^1·7 GPa.
Equilibration temperatures (Table 7) for the studied
lithologies have been obtained using various geothermometric methods (Wells, 1977; Brey & Kohler, 1990; Kohler
& Brey, 1990; Witt-Eickschen & O’Neill, 2005; Ionov &
Sobolev, 2008). The temperature estimates for the spinel
harzburgites obtained using Mg^Fe exchange between
clino- and orthopyroxene (Wells, 1977), the Ca-Opx
method (Brey & Kohler, 1990) and Y distribution between
pyroxenes (Witt-Eickschen & O’Neill, 2005) are in reasonable agreement and range from 830 to 10068C. However,
temperatures based on Ca and Sc exchange between
olivine and clinopyroxene (Kohler & Brey, 1990;
Witt-Eickschen & O’Neill, 2005; Ionov & Sobolev, 2008)
are lower, in the range of 700^9408C, 800^8208C and
720^8208C respectively.
The equilibration temperatures calculated for S1 dunites
vary within the range 700^10008C, and for S2 pyroxenite
veins from 705 to 10398C (Table 7). Because at the estimated pressure range the ‘wet’ solidus of mantle peridotite
is constrained by amphibole stability to a temperature
around 10008C, temperature estimates below 10008C must
reflect re-equilibration between minerals under subsolidus
conditions. This suggests that the mantle section of the
Voykar ophiolite was subjected to rapid solid-state diffusion
processes down to temperatures as low as 7008C. Such low
temperatures of mineral equilibration have been reported
for SSZ-related peridotites (e.g. Parkinson & Pearce,
1998) and possibly indicate water-assisted diffusion and
equilibration in the SSZ environment. However, the
large-scale migration and reactive porous flow of the
melts needed to create the large dunite bodies probably
took place at higher temperatures, in the temperature
interval 1050^12008C. The minimum temperature is constrained by the amphibole stability field at 1000^10508C
(Grove et al., 2006) and corresponds to our maximum
temperature estimates (around 10508C); hydrous melts
below this temperature will react with Cpx producing
significant amounts of amphibole, which did not happen
in the Voykar mantle section. The maximum estimated
temperature of formation of the Voykar dunites is based
on the fact that the surrounding harzburgites do not show
evidence of significant melting (see above). This corresponds to a temperature no higher than 12008C and a
degree of hydrous melting below 3% (Grove et al., 2006).
Two stages of melt migration processes;
geochemistry of percolating melts
In this section we discuss the composition and nature of
the melts (fluids) in the two main stages of melt migration
within the Voykar mantle section.
2512
BATANOVA et al.
MELT TRANSPORT IN SSZ MANTLE
Table 6: Amphibole major and trace element compositions in Voykar mantle lithologies
Sample (pu):
n:
6 39/2
s
6 33/5
s
7 33/5
s
s
67
6 7
6 17/2
MHbl
MHbl
Tsch
MHbl
Tsch
MHbl
7 33/1
MHbl
2
4
3
1
2
3
11
s
SiO2
48·37
0·14
46·92
0·28
45·71
0·11
48·99
45·96
47·76
0·93
49·57
0·41
Na2O
1·75
0·02
1·57
0·04
2·12
0·03
1·55
1·83
1·26
0·16
1·55
0·12
CaO
12·68
0·03
12·61
0·02
12·62
0·06
12·07
12·45
12·73
0·09
12·02
0·06
K2O
0·01
0·01
50·01
50·01
0·05
0·33
0·15
0·06
0·15
0·01
FeO
2·44
0·00
2·88
0·04
2·80
0·05
5·17
4·90
4·71
0·15
4·09
0·03
MgO
19·65
0·07
19·01
0·32
18·49
0·05
19·71
17·94
18·35
0·35
19·69
0·20
Al2O3
10·44
0·18
11·83
0·17
13·12
0·09
8·79
12·07
10·56
0·85
9·02
0·46
0·01
TiO2
0·14
0·01
0·41
0·02
0·43
0·01
0·18
0·26
0·33
0·06
0·10
Cr2O3
1·98
0·03
1·86
0·03
1·78
0·03
0·68
1·27
0·99
0·20
0·37
0·02
MnO
0·05
50·01
0·04
50·01
0·04
50·01
0·08
0·06
0·07
50·01
0·08
50·01
NiO
0·10
0·01
0·10
50·01
0·10
50·01
0·10
0·10
0·09
50·01
Total
97·62
0·01
97·01
0·11
97·22
0·09
97·37
97·16
96·98
0·07
96·64
0·11
Mg-no.
93·48
0·03
92·15
0·11
92·18
0·11
87·18
86·71
87·40
0·54
89·57
0·17
n
Li
2
4
3
1
3
11
5·0
0·4
n.a.
Sc
114·8
2·2
93·5
Ti
883
47
V
444·0
10·7
440·1
7·2
485·0
4·3
547·3
650·8
744·1
13·6
272·0
6·5
Mn
380·6
4·0
351·6
7·2
356·3
3·4
514·4
542·7
600·8
16·2
639·8
17·4
31·0
0·3
Co
Ni
848
5
Cu
0·33
0·03
Zn
7·3
0·7
0·621
Rb
2480
31·9
849
10·7
2·5
39
0·5
10
0·8
6·1
0·5
0·8
2·1
1·1
0·1
9·5
95·9
2·8
118·5
126·2
120·8
7·6
72·1
2671
32·1
890
48
0·2
5
0·27
0·06
8·4
0·2
0·091
0·055
1320
52·0
841
0·25
14·2
48·4
832
0·31
21·2
44·1
750
0·37
11·5
1·3
21
0·07
0·8
615
42·4
743
0·31
20·9
1·7
46
0·4
27
0·04
0·2
0·299
0·023
0·004
0·066
0·779
0·046
1·0
6·5
0·3
10·3
0·8
24·0
25·2
22·0
0·3
6·3
0·3
Y
9·9
0·2
13·2
0·5
20·3
1·0
9·7
8·8
11·6
0·6
3·5
0·3
Zr
2·9
0·1
15·1
0·6
0·4
0·0
1·7
1·8
3·1
0·2
0·6
0·0
Nb
0·082
0·020
0·034
0·005
0·060
0·012
0·143
0·216
0·070
0·016
0·031
0·002
Ba
5·70
3·82
0·18
0·01
0·72
0·53
1·44
3·77
0·30
La
0·155
0·003
0·026
0·001
0·037
0·002
0·077
0·072
0·083
0·006
0·018
0·002
Ce
0·635
0·005
0·123
0·007
0·085
0·009
0·401
0·351
0·411
0·020
0·072
0·005
Pr
0·117
0·004
0·042
0·002
0·012
0·001
0·095
0·096
0·106
0·006
0·015
0·001
Nd
0·679
0·025
0·649
0·012
0·122
0·008
0·764
0·711
0·773
0·049
0·099
0·006
Sm
0·202
0·043
0·740
0·026
0·326
0·008
0·498
0·468
0·476
0·030
0·067
0·004
Eu
0·120
0·004
0·345
0·012
0·195
0·005
0·207
0·194
0·219
0·002
0·027
0·001
Gd
0·585
0·017
1·553
0·045
1·201
0·049
0·897
0·832
1·052
0·051
0·168
0·011
Tb
0·138
0·006
0·295
0·015
0·316
0·014
0·179
0·168
0·220
0·014
0·046
0·003
Dy
1·29
0·03
2·16
0·08
2·91
0·13
1·57
1·33
1·87
0·06
0·45
0·03
Ho
0·365
0·010
0·479
0·023
0·737
0·034
0·354
0·328
0·442
0·025
0·126
0·009
Er
1·290
0·017
1·478
0·055
2·440
0·152
1·101
1·054
1·413
0·099
0·481
0·038
Tm
0·206
0·002
0·218
0·012
0·365
0·016
0·172
0·160
0·213
0·013
0·082
0·006
Yb
1·566
0·002
1·487
0·070
2·529
0·188
1·112
1·090
1·504
0·101
0·649
0·054
Lu
0·239
0·006
0·221
0·011
0·367
0·027
0·179
0·183
0·224
0·019
0·110
0·009
Hf
0·058
0·002
0·404
0·020
0·102
0·003
0·092
0·115
0·193
0·017
0·030
0·002
Pb
0·267
0·074
0·124
0·048
0·125
0·020
0·084
0·205
0·366
0·066
0·565
0·076
2513
114·37
0·930
144
13·1
26·70
2·306
2129
Sr
MHbl, magnesiohornblende; Tsch, tschermakite.
0·452
1640
1·4
13·49
JOURNAL OF PETROLOGY
VOLUME 52
NUMBER 12
DECEMBER 2011
Table 7: Equilibration temperatures calculated for the lithologies of the Voykar mantle section
Sample (pu)
Rock
T W77
211/1
Spl Hz
914
215/7
Spl Hz
940
6 10/2
Spl Hz
6 13
T BK90
T KB90
T IS08
T Sc ol-cpx
898
816
807
783
996
787
817
800
876
957
796
814
775
Spl Hz
914
942
855
819
773
6 16/2
Spl Hz
947
943
928
815
804
6 54/1
Spl Hz
927
866
880
809
772
6 39/2
Spl Hz
904
962
824
811
744
6 25/1
Spl Hz
1001
971
936
816
758
T Y cpx/opx
870
6 12/2
Spl Hz
887
937
790
812
755
7 59/10c
Spl Hz
887
931
789
809
820
7 59/10d
Spl Hz
888
980
787
809
6 24/1
Spl Hz
919
930
838
814
795
932
6 35/2
Spl Hz
888
923
786
810
717
989
Profile: host harzburgite—dunite vein, S1, (Fig. 2b), R
7 15C6
Spl Hz
841
927
735
809
758
7 15C5
Spl Hz
898
1006
840
819
730
7 15C4
Spl Hz
805
752
7 15C1
Du
815
782
7 15C2
Du
813
773
7 15C3
Du
815
800
Dunites, first stage (S1) of melt percolation
6 39/1
Du
971
816
6 38/1
Du
821
771
6 37/1
Du
833
824
6 41
Du
865
858
7 13/1
Du
802
771
6 35/1
Du
215/4
Du
6 21/1
Du*
828
6 23/1
Du
881
6 26/1
Du
999
6 27/1
Du
974
906
931
829
862
802
832
889
Profile: host harzburgite—composite dunite–pyroxenite vein, S2, (Fig. 2e), R
6 11/4
Spl Hz
874
930
769
821
757
6 11/3c
Web
883
877
821
807
733
6 11/3d
Du
815
824
797
910
Profile: host harzburgite—composite dunite–pyroxenite vein, S2, (Fig. 2f), K
6 33/5
Spl Hz
950
1006
889
815
7 33/5
Spl Hz
832
947
701
822
6 33/4
Spl Hz
903
952
849
811
813
6 33/2
Web
907
1039
872
824
762
6 33/1
Web
881
962
796
837
934
7 33/3
Du
6 33/3
Du
7 33/1
Hb Cpxt
768
877
655
823
7 59/10b
Opxt
875
991
770
800
7 59/10a
Cpxt
840
949
708
816
214/7
Web
949
966
895
835
6 12/1
Cpxt
940
980
912
834
763
6 17/2
Cpx
938
925
943
822–885
806
917
834
820
858
Pyroxenite veins, S2
922
(continued)
2514
BATANOVA et al.
MELT TRANSPORT IN SSZ MANTLE
Table 7: Continued
Sample (pu)
Rock
T W77
T BK90
T KB90
T SI08
905
1034
857
910
918
970
870
821–927
T Sc ol–cpx
6 20/4
Cpxt
67
Web
65
Web
7 16/1o
Web
876
964
772
811
705
7 14/2
Web
880
966
783
829
757
7 31/1
Cpxt
T Y cpx–opx
725
825–879
826
923
1019
857
Spl Hz Tmax
1001
1006
936
822
820
989
Spl Hz Tmin
832
866
701
807
717
870
999
889
Du Tmax
802
771
Pxt Tmax
949
1039
943
910
934
922
Pxt Tmin
768
877
655
800
705
826
Du Tmin
Equilibration temperatures calculated according to: W77, Wells (1977); BK90, Brey & Kohler (1990); KB90, Kohler & Brey
(1990); IS08, Ionov & Sobolev (2008); Sc ol–cpx and Y cpx–opx, Witt-Eickschen & O’Neill (2005).
The earlier stage of melt migration (S1) was related to
the origin of the large dunite bodies (Savelieva et al.,
2008). During this stage, stress-focused melt migration
produced dunites as a result of peridotite^melt reaction. It
has been shown (e.g. Kelemen et al., 1995a) that this reaction takes place when the reacted melts come from a
deeper source and thus are unstable with respect to the
host peridotite, being saturated in olivine and undersaturated in pyroxene. It has been demonstrated by both
theory and experiment that the reaction of such melts
with peridotites leads to the dissolution of pyroxenes and
the crystallization of olivine (Kelemen et al., 1995a;
Morgan & Liang, 2003). Indeed, the harzburgite samples
adjacent to dunite or observed as ‘relics’ within the large
dunite bodies have mineral (olivine and Cr-spinel) compositions similar to those of the dunites, thus marking the
reaction zones.
Olivine in the Voykar dunite bodies exhibits a broad
range of compositions, from Fo 90·4 to 92·6 (Fig. 6). In addition to variations in the source composition of the infiltrating melts, this may reflect different original compositions
of the reacted peridotites as well as variations in the ratios
of resorbed and precipitated minerals during melt^rock
interaction (Suhr et al., 2003). The observed decrease in Fo
content in the dunites down to Fo88 within the contact
zone of S2 orthopyroxenite veins (Tables 1 and 3) is probably due to modification of the dunite by late-stage melt
or fluid. However, the olivine in most of the dunites has a
forsterite content similar to that in peridotites far from the
veins (and thus unaffected by melt migration). This leads
us to hypothesize that the melts that reacted with the
peridotites and formed the dunites were originally in equilibrium with a mantle source, which had an Mg-number
similar to that of the host peridotites (Suhr et al., 2003).
The NiO content of olivine in the dunites is usually lower
than that of olivine in the host peridotites, reflecting the
formation of an increasing amount of olivine during the replacement reaction (Suhr, 1999; Suhr et al., 2003).
Most samples of S1 dunites exhibit high spinel
Cr-number coupled with high oxygen fugacity values,
which is typical for SSZ dunites formed by reaction of
island-arc tholeiite or boninite magmas with mantle
peridotite (e.g. Dare et al., 2009).
The concentrations of trace elements in the melts that
migrated through the Voykar mantle can be qualitatively
evaluated by calculating the composition of the melts in
equilibrium with the clinopyroxene from the S1 dunites
and S2 pyroxenites by using clinopyroxene^melt partition
coefficients, in this case for water-rich supra-subduction
melts with low Al2O3 concentrations (Sobolev et al., 1996).
We used variable partition coefficients based on the Al2O3
concentration in the Cpx (Supplementary Data Table 5).
The composition of the melts in equilibrium with Cpx
from the S1 dunite bodies is shown in Fig. 14a.
The clinopyroxenes in the dunites are thought to have
crystallized during the latest stages of melt migration
when the cooling melt percolating inside the channels
reached saturation in olivine and clinopyroxene (e.g.
Kelemen et al., 1995a). These late-stage, water-saturated,
silica-rich melts percolated along the dunite channels and
chemically overprinted information about the melts that
participated in the initial generation of the dunites.
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JOURNAL OF PETROLOGY
VOLUME 52
NUMBER 12
DECEMBER 2011
Fig. 14. Chondrite-normalized trace element compositions of calculated melts in equilibrium with Cpx from the Voykar dunites (a) and
pyroxenites (b) compared with those of high-Ca boninites and boninite-like melts. The field of primary Tonga high-Ca boninites is after
Sobolev & Danyushevsky (1994), Troodos UPL high-Ca boninites and boninite-like volcanic rocks (red lines) from Cameron (1985); field of
primary melts of the Troodos UPL is from Sobolev et al. (1993).
This hypothesis is favoured by the observation that Cpx in
most of the dunite bodies and veins has a composition
close to that of the clinopyroxene in the pyroxenite veins.
However, two samples (pu06 35/1, pu07 15c2) of S1 dunite
contain Cpx grains that differ in their trace element
composition from the Cpx of both the host harzburgites
and the pyroxenite veins (Fig. 10a and b). This observation
suggests that the dunites locally retained captured melt
fractions corresponding to the early stage (S1) of melt
migration and thus preserved information on the geochemical characteristics of their mantle source. As inferred
from the composition of these Cpx grains, the mantle
source that produced the melts was richer in HREE than
the spinel harzburgites surrounding the dunite bodies.
2516
BATANOVA et al.
MELT TRANSPORT IN SSZ MANTLE
Fig. 15. Schematic illustration showing the inferred position of the Voykar mantle section within the SSZ mantle. Thermal structure after
Peacock & Wang (1999); the interval between isotherms is 4008C. 1, 2 and 3 indicate stages of formation of Voykar mantle section (see text).
MORP, mid-ocean ridge protolith.
Concentrations of incompatible elements in these melts
have compositions close to those of boninite-like volcanic
rocks from the Tonga^Mariana supra-subduction zone
(Sobolev & Danyushevsky, 1994) and ophiolite complexes
produced above subduction zones (Cameron, 1985;
Sobolev et al., 1993). However, the melts calculated from
the compositions of Cpx in the Voykar dunites, which
probably were related to S1 melt percolation, have higher
HREE concentrations than the high-Ca boninites of these
complexes (Fig. 14a). This implies that the mantle component of the Voykar source was less depleted in moderately
incompatible elements than the analogous source component of the high-Ca boninites of the Troodos ophiolite and
the Tonga^Mariana system. A sheeted dyke complex composed of boninite-like rocks has been distinguished within
the Voykar ophiolite (Simonov et al., 1998).
The probable age of dunite formation is close to that of
the chromitites in the dunite bodies, which is estimated
at 585 6 Ma (Savelieva et al., 2006).
The late stage (S2) of melt migration apparently correlates with the emplacement of the pyroxenite veins. Melt
migration during this stage probably occurred along fractures (or channels) that are now marked by pyroxenite
and zoned, composite dunite^pyroxenite veins. Most of
the olivine in the pyroxenites has an elevated NiO content
(Fig. 6). This may reflect in situ repartition of Ni into olivine
from pyroxenes owing to decreasing temperature
(Witt-Eickschen & O’Neill, 2005) or to a non-peridotitic
(olivine-free) source for the original melts (Sobolev et al.,
2005). To choose between these alternatives we estimated
the scale of Ni redistribution using the partitioning
of Ni/Mg between olivine and Cpx and Opx
(Witt-Eickschen & O’Neill, 2005), assuming cooling from
1100 to 8008C. The predicted original NiO content in the
olivine at 11008C is shown in Fig. 6. The results suggest
that, despite a significant decrease, the original NiO
content in the high-temperature olivine is still too high to
be in equilibrium with typical mantle peridotite. Similar
features have been reported in olivine from volcanic rocks
in supra-subduction zone environments (Straub et al.,
2008) and were explained by an origin of the parental
melts from a hybridized mantle source formed as a result
of transformation of mantle olivine to orthopyroxene
under the influence of slab-derived fluids or melts.
The reaction relations between the pyroxenite veins and
their host harzburgite (Fig. 2d) and between minerals
within the pyroxenite samples (Fig. 3d) suggest that the
melts or fluids that produced them were oversaturated
in silica. The occurrence of magmatic amphibole in the
pyroxenites indicates that these melts contained significant
amounts of water or even that they were a supercritical
fluid (Bureau & Keppler, 1999; Audetat & Keppler, 2004).
Such fluid-rich melts or fluids have a low viscosity, and
this feature probably can account for their diffuse
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JOURNAL OF PETROLOGY
VOLUME 52
migration from fractures into the host peridotites, which
modified the composition of the latter.
Calculated melts in equilibrium with the Cpx in the
pyroxenite veins are shown in Fig. 14b. The Cpx in S2
dunite from zoned complex dunite^pyroxenite veins has a
similar composition to that in the associated pyroxenite
(Fig. 9a^d) and thus is not considered separately.
The trace element patterns of these melts are also similar
to those of high-Ca boninites.
Thus, we conclude that the source of the Voykar melts
gradually changed its composition and that slab-derived
SiO2-rich, H2O-rich melts or fluids played a significant
role during the late stage of melt^fluid migration. The
incompatible trace element composition of the melts or
fluids from both stages is similar and probably indicates
a slab component.
Tracking history of the Voykar mantle
Taken together, our observations indicate at least three
main stages in the evolution of the Voykar mantle section,
as follows.
(1) Mantle peridotites were initially produced as residues
after moderate degrees (16%) of partial melting,
probably at a spreading centre (oceanic or back-arc).
(2) This mid-ocean-ridge-like peridotite protolith was
involved in intensive high-temperature deformation
and invasion by high-Ca boninite melts, which
resulted in the formation of large bodies of replacive
dunite. It has been suggested that such processes take
place in the forearc mantle during the initial stages
of subduction (Pearce et al., 1992; Morishita et al.,
2011). Estimated P^T conditions of melt percolation
allow us to infer that the Voykar mantle section
was probably located above the melting region
(Fig. 15).
(3) The last stage involved transportation of water- and
silica-rich melts or fluids, which reacted with the
peridotites, producing pyroxenite and composite
dunite^pyroxenite veins. These melts or fluids were
probably transported in cracks, and percolated and
modified the composition of the surrounding harzburgites and dunites. The amount of transported melt
during this stage was significantly lower than during
the dunite formation. We thus suggest that this later
stage took place when the mantle section was horizontally displaced towards the trench (Fig. 15).
The presence of blueschists at the sole of the ophiolitic
allochthon, as well as significant amounts of olivine^antigorite rocks within the Voykar mantle section, also argue
for the forearc position of the Voykar ophiolite (Savelieva
et al., 2002).
NUMBER 12
DECEMBER 2011
AC K N O W L E D G E M E N T S
We acknowledge K.-P. Jochum, B. Stoll and D. Kuzmin for
their assistance with the LA-ICP-MS and EPMA. We
thank N. Mironov, Z. Lyaskovskaya and P. Suslov for
their help in fieldwork in the Polar Urals in 2006^2007.
The insightful reviews of N. Arndt, J. Pearce and two
anonymous reviewers significantly improved the paper.
We greatly appreciate the editorial handling by M. Wilson.
FU NDI NG
This work was supported by the project by the ANR,
France, Chair of Excellence (ANR-09-CEXC-003-01),
Gauss Professorship in Go«ttingen University and Russian
President grant for leading Russian scientific schools
(MX-3919.2010.5) to A.V.S., and grants of the Russian
Foundation for Basic Research 10-05-00011, 09-05-01165
and 09-05-01193.
S U P P L E M E N TA RY DATA
Supplementary data for this paper are available at
Journal of Petrology online.
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