JOURNAL OF PETROLOGY
VOLUME 53
NUMBER 6
PAGES 1255^1285
2012
doi:10.1093/petrology/egs016
On the Recycling of Amphibole-rich Ultramafic
Intrusive Rocks in the Arc Crust: Evidence from
Shikanoshima Island (Kyushu, Japan)
M. TIEPOLO1*, A. LANGONE2, T. MORISHITA3 AND M. YUHARA4
1
CNR^ISTITUTO DI GEOSCIENZE E GEORISORSE^UOS DI PAVIA, PAVIA, ITALY
2
CNR^ISTITUTO DI GEOSCIENZE E GEORISORSE^PISA, PISA, ITALY
3
FRONTIER SCIENCE ORGANISATION, KANAZAWA UNIVERSITY, KANAZAWA, JAPAN
4
DEPARTMENT OF EARTH SYSTEM SCIENCE, FUKUOKA UNIVERSITY, FUKUOKA, JAPAN
RECEIVED MAY 20, 2011; ACCEPTED FEBRUARY 8, 2012
ADVANCE ACCESS PUBLICATION MARCH 15, 2012
New insights into the role of amphibole in arc magma petrogenesis
are provided by the mineral chemistry and U^Pb geochronology of
Cretaceous amphibole-rich mafic rocks and associated granitoids
from Shikanoshima Island (Kyushu, Japan). In the northeastern
part of Shikanoshima Island a relatively large body (about 600 m
in length) of amphibole-rich mafic rocks is found within granodiorite host-rocks. The core of the mafic body consists of amphibole-rich
gabbrodiorite with a porphyritic texture.Towards the host granodiorite the porphyritic texture is progressively lost and a band of relatively
homogeneous medium- to fine-grained mafic rock marks the boundary with the granitoid rocks.The amphibole-rich porphyritic gabbrodiorite consists of large amphibole grains (up to 60 vol. %)
characterized by brown cores, occasional inclusions of clinopyroxene,
and green rims. These large amphibole grains are dispersed in a
fine-grained matrix consisting of green amphibole, clinopyroxene
and plagioclase. Literature whole-rock data on the mafic rocks from
Shikanoshima Island suggest that they are the intrusive counterparts
of high-Mg andesite (HMA). Major and trace element mineral
compositions reveal a marked chemical contrast between the brown
amphibole (and its inclusions) and the matrix minerals, suggesting
that they are not on the same liquid line of descent. The brown
amphibole and its clinopyroxene inclusions were inherited from
amphibole-rich ultramafic intrusive crustal rocks (e.g. hornblendites) crystallized from a melt with a chemical composition close to
that of continental arc basalts. U^Pb geochronological data suggest
that the xenocrystic material is about 20 Myr older than the matrix
minerals. The matrix mineral crystallized from a parental liquid
similar to sanukite-type HMA and with a trace element signature
characterized by strong enrichment in elements with high crustal
*Corresponding author. E-mail: [email protected]
affinity and depletion in heavy rare earth elements. Green amphibole
is a common mineral in all the studied lithologies; this allowed us
to monitor the compositional variations in the liquid from which it
crystallized moving from the core of the mafic complex to the host
granodiorite.The data reveal that the interstitial melt had interacted
with a melt enriched in elements with a high crustal affinity that,
given the close association in the field, is inferred to be the host granitoid. These results favour an origin for sanukite-type HMA not
from primary mantle melts but from mantle melts that have been affected by crustal processes and have been contaminated by crustal material. The major and trace element composition of the brown
amphibole from the Shikanoshima Island mafic rocks is compared
with that of brown amphibole from other amphibolite-rich intrusive
rocks in orogenic settings worldwide (Alpine chain and Ross
Orogen). The observed similarities suggest that the amphibole-rich
mafic rocks are the expression of a magmatic process with a common
geochemical affinity that is independent of the age and local geodynamic setting and thus related to a specific petrogenetic process.
Amphibole-rich mafic and ultramafic intrusive rocks could be a
common feature of all collisional systems and thus represent a
‘hidden’amphibole reservoir in the arc crust.We show that amphibole
plays a major role in the petrogenesis of sanukite-type HMA but is
also expected to play a major role in the differentiation of many
other arc magmas.
KEY WORDS:
amphibole; andesite; zircon; xenocryst; U^Pb dating;
trace element
ß The Author 2012. Published by Oxford University Press. All
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JOURNAL OF PETROLOGY
VOLUME 53
I N T RO D U C T I O N
The role of amphibole in arc magma petrogenesis is not
completely understood. Although amphibole is rarely a
phenocryst in arc lavas, many volcanic products in arc settings seem to be residual after cryptic amphibole crystallization at mid- to lower crustal depths, thus implying the
occurrence of amphibole-rich cumulates in the arc crust
and thus of a ‘hidden’ amphibole reservoir (Davidson
et al., 2007). Amphibole-rich mafic and ultramafic intrusive
rocks (mainly hornblendites, amphibole-gabbros and
amphibole-diorites) have been reported worldwide from
orogenic settings (e.g. Ulmer et al., 1983; Kemp, 2004;
Tiepolo & Tribuzio, 2008; Leuthold et al., 2009; Quian &
Hermann, 2010) but their role in arc magma petrogenesis
is debated.
Kamei et al. (2004) showed that some amphibole-rich
mafic intrusive rocks from Kyushu (Japan) have major
and trace element bulk-rock compositions that approximate high-Mg diorite and may thus be considered to be
the intrusive counterpart of high-Mg andesite (HMA).
The HMAs are a group of subduction-related magmas
whose origin is still debated; they are considered as primary melts originating either from hydrated mantle
wedge peridotite (e.g. Grove et al., 2002) or from the subducting lithosphere followed by equilibration with the
mantle wedge peridotite (Kay, 1978; Pearce et al., 1992;
Yogodzinski et al., 1994; Kelemen, 1995; Shimoda et al.,
1998; Rapp et al., 1999; Tatsumi, 2001; Hanyu et al., 2002;
Wood & Turner, 2009). HMA petrogenesis has also been
attributed to mixing of primary basaltic melts with melts
produced by partial melting of pre-existing lower mafic
arc crust (Tatsumi, 2000), or to mixing between dacitic
and basaltic magmas and entrainment of ultramafic crustal material (Streck et al., 2007). More recently, HMA
petrogenesis by amphibole crystallization and concomitant
assimilation of ultramafic crust has also been proposed
(Tiepolo et al., 2011).
We address here both the problem of the role played by
amphibole in arc magma petrogenesis, specifically in arc
crust processes that may be hidden from view, and the
origin of HMA. We have carried out a combined in situ
geochemical and geochronological study on amphibolerich mafic intrusive rocks with HMA affinity (Yuhara &
Uto, 2007) and associated granitoids from Shikanoshima
Island (Kyushu, Japan). The coupling of textural information, microchemical data and in situ zircon geochronology
has allowed us to show that older (up to 20 Myr)
amphibole-rich ultramafic rocks were assimilated by a
mafic melt that was subsequently partially hybridized
with granitoids at the emplacement level. These results
are further evidence that melts close to HMA in composition can be obtained by differentiation processes at crustal
depths. The comparison with other amphibole-rich mafic
and ultramafic rocks of different ages worldwide has
NUMBER 6
JUNE 2012
revealed striking similarities. This suggests that
amphibole-rich mafic intrusive rocks with HMA affinity
may be a relatively common product of arc magmatism
and confirms that amphibole may play an active role in
arc magma differentiation processes.
GEOLOGIC A L S ET T I NG
In Kyushu granitoid rocks of Cretaceous age are exposed
from the northern to the central part, and are delimited towards the south by the Usuki^Yatsushiro tectonic line
(Kamei et al., 2004; Fig. 1a). The age of emplacement
varies from about 121 to 76 Ma (e.g. Osanai et al., 1993;
Kamei et al., 1997; Owada et al., 1999); a progressive northward shift of the igneous activity has been proposed
(Owada et al., 1999). The Cretaceous granitoid rocks intrude various kinds of lithologies: low- and high-pressure
metamorphic rocks, Permian accretionary complexes,
Jurassic^Triassic granites and Cenozoic volcanic rocks.
Locally, amphibole-rich mafic intrusive rocks are associated with the granitoids. They have been reported from
Shikanoshima Island (Yuhara & Uto, 2007) in the Taku
area (Owada et al., 1999, and references therein) and in
the Kunisaki Peninsula (Murakami, 1994; Kamei et al.,
2004). Some of these mafic intrusive rocks have bulk-rock
chemical compositions suggesting that they are the intrusive counterparts of high-Mg andesite.
The age relationships between the mafic and granitoid
rocks in the different areas are unclear. Several researchers
have suggested coeval intrusion (Nakajima et al., 2004;
Yuhara & Uto, 2007); however, an older age for the mafic
intrusive rocks has also been proposed (e.g. Orikabe
Plutonic Complex; Mikoshiba et al., 2004). According to
some workers, the mafic rocks may even post-date the associated granitoids (e.g. Kunisaki Peninsula: Murakami,
1994; Kamei et al., 2004). Specific geochronological data
on the mafic rocks are scarce. An age of 98·7 4·9 Ma
(K^Ar on amphibole) was obtained for a high-Mg dioritic
dyke in the Kunisaki Peninsula (Kamei et al., 2004).
Owada et al. (1999), on the basis of the field relations with
the surrounding granites and metamorphic rocks, suggested emplacement of a gabbroic body in the Taku area
at about 116 Ma. Karakida et al. (1994) reported a K^Ar
amphibole age of 101 5·0 Ma for the Shikanoshima basic
rocks
F I E L D R E L AT I O N S A N D
P E T RO G R A P H Y
Shikanoshima Island is located in the northwestern sector
of Kyushu and consists of the Shikanoshima granodiorite,
the Kitasaki tonalite and the Shikanoshima basic rocks
(Karakida et al., 1994, and references therein). The best exposure and the best relations between granodioritic rocks
and mafic rocks are in the northeastern part of
1256
TIEPOLO et al.
AMPHIBOLE IN ARC MAGMA PETROGENESIS
Russia
Cretaceous
China
(a)
Granitic rocks
North
Korea
South
Korea
Tonalitic/granodioritic rocks
Japan
Jurassic-Triassic
Kyushu Island
Granitic rocks
130°30’E
N
Shikanoshima
Island
33°68’N
Taku
ine
ic l
n
o
t
tec
ro
i
h
us
ats
i-Y
k
u
Us
50 km
Akase
Genkai Sea
(b)
N
Kurose
Alluvium
Shikanoshima Granodiorite
Shikanoshima basic rocks
Medium-grained qtz diorite
Coarse-grained gabbro
0
200m
Fig. 1. (a) Geological sketch map of northern Kyushu showing the location of Shikanoshima Island. (b) Simplified sketch map of the northeastern part of Shikanoshima Island (slightly modified after Yuhara & Uto, 2007) showing the boundaries between intrusive units and the sampling
area (rectangle).
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JOURNAL OF PETROLOGY
VOLUME 53
Shikanoshima Island where a relatively large body (about
600 m in length) of amphibole-rich mafic rocks is found
within the granodiorite (Fig. 1b).
According to Yuhara & Uto (2007) and Yuhara et al.
(2009) the Shikanoshima basic rocks comprise both mafic
dykes and large mafic blocks. The mafic dykes consist of
fine- to medium-grained quartz diorite, occasionally showing chilled margins and mingling relations with the host
granodiorite (Yuhara et al., 2005b, 2006, 2009). The chemical composition of these dykes is similar to that of the enclaves in the granodiorite (Yuhara et al., 2005b, 2006,
2009). The mafic blocks have dimensions from tens of
metres to several hundred meters and are surrounded by
the Shikanoshima Granodiorite (Fig. 2a). The core of the
mafic bodies consists of amphibole-rich gabbrodiorite with
a porphyritic texture (coarse-grained hornblende gabbro
of Yuhara & Uto, 2007; Fig. 2b and c). Amphibole is a
pseudo-phenocrystic phase. It forms up to 60^65 vol. % of
the rock and is characterized by brown cores and green
rims. The proportions of brown to green amphibole are
variable. Frequently, brown amphibole constitutes the majority of the crystal (Fig. 3), but occasionally it is only a
minor portion of the core of the grain (Fig. 4a). In both
cases, the boundary between the two amphiboles is relatively sharp and the transition occurs over 100 mm.
Occasionally, the outermost green amphibole at the contact with the matrix shows oscillatory zoning, with intercalations of narrow light green and dark green domains
(Fig. 4b). The light green amphibole rim typically has a
thickness of about 500 mm and contains inclusions of irregularly shaped plagioclase and titanite. Titanite is
always associated with plagioclase and usually occurs at
the transition between the brown and the light green
amphibole domains (Fig. 4c). Clinopyroxene inclusions
(up to 1·5 mm in dimension), which are relatively abundant
in the brown amphibole, are characterized by exsolution
lamellae and lobate boundaries. The pseudo-phenocrystic
amphiboles are dispersed in a fine-grained matrix consisting of green amphibole, clinopyroxene, plagioclase and
minor titanite and quartz (Fig. 4d). Acicular apatite,
zircon, rutile and rare K-feldspar are accessory phases.
Matrix green amphibole has a subhedral to euhedral
habit without optical zoning. Matrix clinopyroxene is
smaller than matrix amphibole (0·05^0·5 mm), has a
sub-rounded shape and does not show exsolution lamellae.
Towards the host Shikanoshima granodiorite, at about
60 m from the contact, the porphyritic texture of the diorite [medium-grained biotite^hornblende-bearing quartz
diorite of Yuhara & Uto (2007)] is progressively lost and a
band of a relatively homogeneous medium- to fine-grained
mafic rock marks the boundary with the host granitoid
rocks. The medium-grained quartz diorite consists mostly
of green amphibole (up to 80 vol. %), and the porphyritic
texture is poorly developed (Fig. 3). The occurrence of
NUMBER 6
JUNE 2012
brown amphibole is restricted to irregular patches in the
larger green amphibole grains. Noticeably, the outermost
rim of both large and small green amphibole grains are
light green in colour. Clinopyroxene is limited to small anhedral grains within the brown amphibole patches. Biotite
flakes of secondary origin are occasionally found in the
brown amphiboles. Plagioclase, K-feldspar, quartz and
biotite are fine-grained, minor phases (c. 10 vol. %) in the
rock. Acicular apatite, zircon and opaque minerals are
accessory minerals.
The Shikanoshima granodiorite hosting the mafic body
is in a medium-grained massive to weakly foliated hornblende^biotite granodiorite. Plagioclase, quartz, biotite,
K-feldspar and hornblende are the major minerals.
Apatite, titanite, zircon, allanite, epidote and opaques are
accessory phases.
Medium-grained biotite granodiorite and granite
dykes with straight boundaries and no chilled margins
(biotite granite of Yuhara & Uto, 2007) crosscut the
Shikanoshima basic rocks (Fig. 2d). Locally, hornblende^
biotite tonalite to granodiorite dykes with irregular boundaries with the mafic rocks are also found.
In this study we focused on the mafic bodies and we collected samples from the same area as Yuhara & Uto
(2007). A total of six samples representative of the different
rock types in the mafic body were selected for in situ chemical and geochronological studies (Fig. 3). Four samples
are representative of the amphibole-rich porphyritic gabbrodiorite at the core of the mafic body. One sample is representative of the medium-grained quartz diorite close to
the contact with the granitoid rocks and one sample is representative of the host granodiorite.
B U L K- RO C K C H E M I S T RY
The major and trace element composition of the
Shikanoshima Island mafic and granitoid rocks has been
reported by Yuhara & Uto (2007). Below, we provide a
brief summary of the major features and differences between the different rock types.
The amphibole-rich porphyritic gabbrodiorite and the
medium-grained quartz diorite are almost comparable in
terms of bulk-rock composition. The porphyritic gabbrodiorite is characterized by relatively high SiO2 (50·5^
55·4 wt %) and MgO (9·0^16·4 wt %), and low Al2O3
(7·4^11·6 wt %) contents. Medium-grained quartz diorites
extend the above ranges towards slightly more evolved
compositions: SiO2 51·1^59·4 wt %, MgO 6·6^15·6 wt %
and Al2O3 8·1^15·3 wt %. Harker diagrams for both
major and trace elements reveal almost continuous trends
between the quartz diorite dykes and the host granodiorite.
According to Yuhara & Uto (2007), the bulk-rock composition of the mafic rocks from Shikanoshima Island is consistent with a sanukite-type HMA (Fig. 5).
1258
TIEPOLO et al.
AMPHIBOLE IN ARC MAGMA PETROGENESIS
(a)
(b)
(c)
(d)
Fig. 2. (a) Main mafic body consisting of amphibole-rich gabbrodiorite with a porphyritic texture. (b, c) Details showing the porphyritic texture of the amphibole-rich gabbrodiorite characterized by large brown amphibole grains (up to 1cm) dispersed in a more fine-grained matrix
containing both mafic and felsic minerals. (d) Granite dykes with straight boundaries crosscutting the Shikanoshima basic rocks.
1259
JOURNAL OF PETROLOGY
VOLUME 53
NUMBER 6
JUNE 2012
Petrographic features of mafic rocks
SK 16
SK 14
Amph-rich porphyritic gabbrodiorite
medium-grained Qtz-diorite
Mg-Hbl
Ti-Prg
Cpx
Mg-Hbl
0.5 cm
0.5 cm
Towards granodiorite
Quartz - K-feldspar - Biotite
Ti-Prg - Cpx
Far from the contact
with granitoids
Mineral
Near the contact
with granitoids
Brown-Amph
Cpx in brown-Amph
Green-Amph
Cpx in matrix
Pl
Bt
Qtz + Kfs
Ttn + Ap + Zrn + Oxides
Fig. 3. Appearance of amphibole-rich porphyritic gabbrodiorite and medium-grained Qtz-diorite at the thin section scale. Lower panel
illustrates the petrographic variations towards the contact with the granitoid.
A N A LY T I C A L P RO C E D U R E S
Major and trace element geochemistry
Major element mineral composition was determined at the
Dipartimento di Scienze della Terra Universita' di Milano
using a JEOL JXA 8200 Superprobe equipped with five
wavelength-dispersive (WDS) spectrometers. Pyroxene,
amphibole and titanite were analysed using a 1 mm beam
at 15 kV and a 15 nA beam current. Alkali-feldspars were
analysed using a 5 mm beam at 15 kVand a 5 nA beam current. Natural and synthetic minerals and glasses were
1260
TIEPOLO et al.
AMPHIBOLE IN ARC MAGMA PETROGENESIS
green amph
Cpx
Pl
(a)
green amph
(b)
Cpx
brown
amph
browm amph
1 mm
1 mm
(c)
Ttn
Cpx
green amph
Pl
(d)
Amph II
1 mm
1 mm
Fig. 4. Photomicrographs (parallel Nicols) of the amphibole-rich porphyritic gabbrodiorite and medium-grained Qtz-diorite. (a, b) Overview
of amphibole zoning in the amphibole-rich porphyritic gabbrodiorite. (Note the mineral inclusions at the core of the grain.) (c) Inclusions of
titanite and plagioclase in the green amphibole of the medium-grained Qtz-diorite. (d) Detail of the matrix minerals in the amphibole-rich porphyritic gabbrodiorite.
used as standards. In particular, omphacite USNM110607
and albite were used as a standard for Na, olivine
USNM2566 for Mg, anorthite USNM137041 for Al, wollastonite for Ca and Si, K-feldspar PSU-Or1A for K, ilmenite
USNM96189 for Ti, chromite USNM117075 and pure Cr
for Cr, rodonite for Mn, fayalite USNM85276 for Fe, and
nickeline and pure Ni for Ni. All standards were calibrated
within 0·5% at one standard deviation. Raw data were
corrected using a Phi-Rho-Z quantitative analysis
program.
Trace element mineral composition was determined by
laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) at the CNR^Istituto di Geoscienze e
Georisorse, UO di Pavia. The instrument couples a
Nd:YAG laser working at 266 nm with a quadrupole
ICPMS Perkin Elmer type DRCe system. Selected masses
were acquired in peak hopping mode and each analysis
consisted of the acquisition of 1min of background and
1min of ablation signal. Further details on the analytical
method have been reported by Tiepolo et al. (2003).
The laser was operated at 10 Hz with a pulse energy on
the sample of 0·01^0·03 mJ. The spot size was set to
20^40 mm. Data reduction was performed with the
‘GLITTER’ software package (van Achtenbergh et al.,
2001) using NIST SRM 612 as the external standard and
44
Ca or 29Si as the internal standard. Precision and accuracy, assessed during each analytical run on the BCR-2
USGS reference glass, are better than 6% relative. Major
and trace element mineral compositions are reported in
Tables 1^8 and Supplementary Data Appendices 1^4
(available for downloading at http://www.petrology
.oxfordjournals.org).
U^Pb geochronology
Zircon grains were separated from one porphyritic gabbrodiorite and from the host Shikanoshima granodiorite
using standard magnetic techniques and heavy liquids.
Prior to age determination, zircon grains were examined
1261
JOURNAL OF PETROLOGY
VOLUME 53
MgO wt%
20
15
10
5
0
40
50
60
70
80
SiO2 wt%
1000
JUNE 2012
with a frequency of 5 Hz and with a fluency of 12 J cm2.
Mass bias and laser-induced fractionation were corrected
by adopting zircon 91500 as an external standard
(1062·4 0·4 Ma; Wiedenbeck et al., 1995). The same spot
size (20 mm) and integration intervals were used on both
standard and unknown samples. Data reduction was carried out using the ‘GLITTER’ software package (van
Achterbergh et al., 2001) setting the error of the external
standard at 1%. Time-resolved signals were carefully inspected to detect perturbations of the signal related to inclusions, cracks or mixed age domains. Within the same
analytical run, the error associated with the reproducibility of the external standards was propagated to each analysis of a sample (see Horstwood et al., 2003); following
this procedure each age determination is accurate within
the quoted error. All errors in the text are given at 2s
level. During each analytical run, reference zircon 02123
(295 Ma; Ketchum et al., 2001) was analysed together with
the unknowns for quality control (Table 9). The concordia
test was performed for each analytical spot from
206
Pb/238U and 207Pb/235U ratios using the function in the
software package Isoplot/Ex3.00 (Ludwig, 2000). It should
be noted that the error associated with the mean concordia
ages was calculated as the mean of the errors of the single
analyses. Geochronological data are reported in Table 9.
Standard determinations are reported in Supplementary
Data Appendix 5.
amph-rich porphyritic
gabbrodiorites
medium grained Qtz-diorites
Shikanoshima granodiorite
(main facies)
granitic dykes
(a)
NUMBER 6
Sr/Y
(b)
bajaitic HMA
100
M I N E R A L C H E M I S T RY
Amphibole
boninitic HMA
10
sanukitic HMA
1
1
10
100
Y (ppm)
Fig. 5. Representative whole-rock major and trace element compositions of amphibole-rich porphyritic gabbrodiorites, medium-grained
Qtz-diorites and associated granitoid rocks. Data are from Yuhara &
Uto (2007). (a) MgO vs SiO2 (wt %); (b) Sr/Y vs Y (ppm)
with a scanning electron microscope (SEM) by cathodoluminescence (CL).
Age determinations were carried out at the CNR^
Istituto di Geoscienze e Georisorse, UO of Pavia using
a 193 nm ArF excimer LA microprobe (GeoLas200
QMicrolas) coupled to a magnetic sector Thermo
Finnigan Element 1 ICPMS system. Full analytical details
have been given by Tiepolo (2003). The laser was operated
Brown amphibole in the amphibole-rich porphyritic gabbrodiorite is mostly Ti-pargasite with Mg# [Mg/
(Mg þ FeT)] ranging between 0·67 and 0·72 (Fig. 6). No
significant intra-grain zoning was observed. The TiO2 contents are high (1·10^2·06 wt %) and Al2O3 varies from
11·01 to 12·20 wt % (Fig. 6). The chondrite-normalized
REE pattern (Fig. 7a) is bell-shaped with light rare earth
element (LREE) and heavy REE (HREE) depletion relative to middle REE (MREE) (LaN/SmN ¼ 0·4^0·8; GdN/
YbN ¼1·5^2·2), which are 30 times C1 chondrite. The incompatible element pattern (Fig. 7b) reveals a strong depletion in Rb, Pb and Zr^Hf relative to the neighbouring
elements. A positive Ti anomaly is observed and Cr contents vary between 476 and 1961ppm.
In amphibole-rich porphyritic gabbrodiorite the
green amphibole in the matrix and the green amphibole
rimming the brown amphibole cores varies from
Mg-hornblende to actinolite in composition. Compared
with the brown amphibole, they have slightly higher
Mg# (0·68^0·78) and lower Al2O3 (1·45^9·01) and TiO2
contents (0·01^0·95 wt %; Fig. 6). The light green amphibole at the rim of the brown amphibole crystals generally
has lower TiO2, Al2O3 and alkali contents than the green
amphibole in the matrix. The chondrite-normalized REE
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TIEPOLO et al.
AMPHIBOLE IN ARC MAGMA PETROGENESIS
Table 1: Representative major element composition (wt %) of amphibole (cations are normalized to 23 oxygens)
Sample:
SK16A SK16A SK15A SK16B SK16B SK16A SK16A SK15A SK16B SK16B SK16B SK14
Rock type:
Pgbdr
Amph type: B
SK14
SK14
SK11
Pgbdr
Pgbdr
Pgbdr
Pgbdr
Pgbdr
Pgbdr
Pgbdr
Pgbdr
Pgbdr
Pgbdr
Qtz-dr
Qtz-dr
Qtz-dr
Grd
SK11
Grd
B
B
B
B
G
G
G
G
G
G
G
G
G
G
G
SiO2
43·95
43·67
44·77
43·49
43·62
49·98
52·23
53·21
47·10
53·14
53·17
50·55
55·59
52·79
48·06
47·97
TiO2
2·56
2·48
2·01
2·20
2·59
0·93
0·60
0·64
0·88
0·56
0·56
0·24
0·12
0·31
0·94
0·95
Al2O3
12·19
12·06
11·80
11·62
12·20
7·52
5·05
4·58
9·01
4·08
3·90
7·54
3·20
5·04
6·11
6·79
Cr2O3
0·11
0·06
0·17
0·05
0·09
0·14
0·21
0·20
0·32
0·13
0·14
0·19
0·09
0·35
0·02
0·01
FeOT
11·02
10·84
10·36
10·33
11·24
11·00
10·35
8·83
12·04
9·67
9·54
9·11
6·88
7·82
15·49
15·64
MnO
0·18
0·15
0·13
0·17
0·18
0·20
0·19
0·19
0·23
0·21
0·21
0·16
0·17
0·20
0·85
0·80
NiO
–
–
–
0·08
0·00
–
–
–
0·00
0·04
0·02
0·02
0·09
0·00
0·00
0·00
MgO
13·96
14·15
14·59
14·85
13·54
15·53
16·41
17·57
14·27
17·16
17·24
17·07
19·51
18·07
12·95
12·69
CaO
12·02
12·05
12·37
11·54
12·22
12·30
12·45
12·52
11·70
12·49
12·46
11·71
11·94
12·03
11·42
11·44
Na2O
2·12
2·04
1·93
2·04
1·69
1·27
0·80
0·74
1·58
0·61
0·59
1·15
0·54
0·85
1·04
1·32
K2O
0·68
0·69
0·70
0·68
0·72
0·35
0·37
0·27
0·42
0·28
0·23
0·39
0·05
0·08
0·54
0·62
Total
98·84
97·06
98·10
99·22
98·66
98·75
97·56
98·37
98·06
98·14
98·19
97·54
97·42
98·23
98·84
97·06
Si
6·247
6·258
6·362
6·277
6·276
7·110
7·439
7·527
6·823
7·581
7·607
7·191
7·790
7·488
7·197
7·136
Ti
0·274
0·267
0·215
0·239
0·280
0·100
0·065
0·068
0·096
0·060
0·060
0·026
0·013
0·034
0·106
0·107
Al
2·043
2·038
1·977
1·977
2·069
1·261
0·848
0·764
1·539
0·686
0·658
1·265
0·529
0·843
1·079
1·191
Cr
0·012
0·007
0·019
0·006
0·011
0·015
0·024
0·023
0·037
0·015
0·016
0·021
0·010
0·039
0·002
0·001
Fe
1·258
1·299
1·231
1·182
1·353
1·309
1·233
1·045
1·459
1·154
1·142
1·084
0·806
0·928
1·940
1·946
Mn
0·021
0·018
0·016
0·021
0·022
0·024
0·023
0·023
0·029
0·026
0·026
0·019
0·020
0·023
0·108
0·101
Ni
–
–
–
0·009
0·000
–
–
–
0·000
0·004
0·002
0·002
0·010
0·000
0·000
0·000
Mg
2·955
3·020
3·088
3·192
2·902
3·291
3·481
3·702
3·079
3·646
3·674
3·617
4·072
3·818
2·888
2·812
Ca
1·831
1·850
1·884
1·785
1·884
1·875
1·900
1·898
1·816
1·909
1·910
1·785
1·793
1·829
1·832
1·823
Na
0·584
0·567
0·532
0·571
0·471
0·351
0·221
0·202
0·444
0·168
0·163
0·318
0·147
0·234
0·302
0·380
K
0·122
0·125
0·127
0·125
0·132
0·063
0·067
0·049
0·078
0·050
0·042
0·072
0·010
0·014
0·104
0·117
Mg#
0·693
0·699
0·715
0·719
0·682
0·72
0·74
0·78
0·68
0·76
0·76
0·77
0·83
0·80
0·60
0·59
Pgbdr, amph-rich porphyritic gabbrodiorite; Qtz-dr, medium-grained quartz-diorite; Grd, granodiorite; B, brown; G, green.
patterns of the light green amphibole rims (Fig. 7c) are
characterized by LREE enrichment relative to the
MREE^HREE (LaN/SmN ¼ 0·9^2·5; LaN/YbN ¼ 2·4^
4·6), which are almost flat at about 6^16 times C1 chondrite. Peculiar to the green amphibole in the matrix is the
inverted U-shape of the LREE, characterized by LaN/
CeN ratios 51. The incompatible element patterns reveal
strong depletion in Rb, Sr and Zr relative to the neighbouring elements (Fig. 7d). A large variability (exceeding
an order of magnitude) is observed for U, Th, Nb and Ta.
Cr contents in green amphibole are higher than in brown
amphibole (814^3046 ppm).
Green amphibole in the medium-grained quartz diorite
corresponds to Mg-hornblende to actinolite, and compositionally closely resembles the green amphibole found in
the matrix of the amphibole-rich porphyritic gabbrodiorites. The Mg# ranges from 0·76 to 0·83 (Fig. 6). TiO2 and
Al2O3 contents vary from 0·12 to 0·49 wt % and from
2·93 to 7·96 wt %, respectively (Fig. 6). The lower TiO2
and Al2O3 contents are observed in the light green amphibole rims. The chondrite-normalized REE patterns
(Fig. 7e) are characterized by LREE enrichment relative
to the HREE (LaN/SmN 1·4^4·0), which are about 3^10
times C1 chondrite. The incompatible trace element patterns (Fig. 7f) reveal marked negative anomalies in Rb, Sr
and Ti relative to neighbouring elements. Pb contents are
in the range 0·35^1·36 ppm. Ni contents (220^385 ppm)
are significantly higher than in green amphibole from the
amphibole-rich porphyritic gabbrodiorite; however, Cr
contents are comparable (791^2905 ppm).
The green amphibole from the granodiorite is
Mg-hornblende in composition. The Mg# is markedly
lower (0·59^0·60) than that of the green amphibole in the
mafic lithologies (Fig. 6). However, TiO2 (0·87^1·07 wt %),
Al2O3 (6·11^679 wt %) and Na2O (0·74^1·32 wt %) contents are comparable (Fig. 6). The chondrite-normalized
1263
JOURNAL OF PETROLOGY
VOLUME 53
NUMBER 6
JUNE 2012
Table 2: Representative major element composition (wt %) of clinopyroxene from amph-rich porphyritic gabbrodiorites
Sample:
Tex. pos.:
SK16A
Inc Amph
SK15A
Inc Amph
SK16B
Inc Amph
SK16B
Inc Amph
SK16B
Inc Amph
SK16A
matrix
SK15A
matrix
SK16B
matrix
SK16B
matrix
SiO2
TiO2
Al2O3
Cr2O3
FeOT
MnO
NiO
MgO
CaO
Na2O
Total
Si
Ti
Al
Cr
Fe2þ
Fe3þ
Mn
Ni
Mg
Ca
Na
Mg#
54·56
0·18
1·47
0·40
4·87
0·17
0·00
15·71
23·51
0·33
101·20
1·977
0·005
0·063
0·011
0·148
0·000
0·005
0·000
0·849
0·913
0·023
0·85
55·02
0·13
0·67
0·25
3·91
0·18
0·00
15·99
25·04
0·16
101·35
1·989
0·004
0·028
0·007
0·118
0·000
0·005
0·000
0·862
0·970
0·011
0·88
54·01
0·15
1·50
0·32
5·34
0·26
0·02
15·37
23·36
0·40
100·75
1·971
0·004
0·065
0·009
0·159
0·004
0·008
0·001
0·836
0·914
0·028
0·84
53·64
0·25
1·72
0·61
5·11
0·16
0·01
16·80
21·99
0·25
100·54
1·953
0·007
0·074
0·018
0·150
0·006
0·005
0·000
0·912
0·858
0·018
0·85
54·27
0·16
1·31
0·31
5·11
0·18
0·01
15·77
23·17
0·34
100·64
1·978
0·004
0·056
0·009
0·156
0·000
0·006
0·000
0·857
0·905
0·024
0·85
54·84
0·09
0·99
0·17
5·82
0·18
0·00
15·48
23·61
0·28
101·46
1·989
0·003
0·042
0·005
0·177
0·000
0·006
0·000
0·837
0·918
0·020
0·83
54·88
0·10
1·09
0·11
6·28
0·25
0·00
15·06
23·83
0·23
101·83
1·988
0·003
0·047
0·003
0·190
0·000
0·008
0·000
0·813
0·925
0·016
0·81
54·18
0·08
0·70
0·13
6·29
0·27
0·00
14·53
24·25
0·30
100·90
1·986
0·002
0·030
0·004
0·174
0·018
0·008
0·000
0·794
0·953
0·021
0·80
54·02
0·10
0·58
0·07
6·23
0·24
0·00
14·81
24·20
0·29
100·64
1·984
0·003
0·025
0·002
0·166
0·025
0·007
0·000
0·811
0·952
0·020
0·81
Tex. pos., textural position; Inc Amph, included in amphibole.
REE patterns (Fig. 7e) parallel those of the green amphibole from the medium-grained quartz diorite but at significantly higher concentrations (HREE are up to 50 time C1
chondrite). Other distinctive features are the marked
negative Eu anomalies (Eu/Eu* ¼ 0·31^0·46) and the
more pronounced bell-shaped pattern of the LREE (La/
Ce ¼ 0·54^0·65). The incompatible trace element patterns
(Fig. 7f) reveal more marked negative anomalies in Rb,
Zr^Hf and Ti relative to the mafic lithologies. Pb contents
are significantly higher than those of the green amphibole
in the mafic rocks (1·7^2·5 ppm). The Cr and Ni contents
are very low and range from 61 to 493 ppm and 50 to
58 ppm, respectively.
Clinopyroxene
Clinopyroxene within brown amphibole in the
amphibole-rich porphyritic gabbrodiorite is diopsidic in
composition with a relatively high Mg# (0·82^0·88;
Fig. 8). The Al2O3 and TiO2 contents are variable and
range from 0·59 to 2·12 wt % and 0·06 to 0·29 wt %, respectively (Fig. 8). The chondrite-normalized REE patterns are characterized by a slight depletion in LREE
(LaN/SmN ¼ 0·65) relative to MREE^HREE, which
are nearly flat at about 7^8 times C1 chondrite (Fig. 9a).
Table 3: Representative major element composition (wt
%) of feldspars
Sample:
SK16A SK15A SK16B SK16B SK16B SK14 SK14 SK14
Rock type: Pgbdr Pgbdr Pgbdr Pgbdr Pgbdr Qtz-dr Qtz-dr Qtz-dr
Feldspar: Pl
Pl
Pl
Pl
K-fsp Pl
Pl
Pl
SiO2
Al2O3
FeOT
CaO
Na2O
K2O
Total
Si
Al
Fe
Ca
Na
K
An
Ab
Or
56·16
28·05
0·20
10·67
5·41
0·20
100·69
10·04
5·910
0·030
2·040
1·880
0·050
51·4
47·4
1·3
58·86
26·26
0·16
8·68
6·72
0·17
100·85
10·45
5·490
0·020
1·650
2·310
0·040
41·3
57·8
1·0
61·89
24·52
0·18
6·25
7·61
0·14
100·59
10·91
5·090
0·030
1·180
2·600
0·030
31·0
68·2
0·8
61·03
24·63
0·11
6·89
7·22
0·19
100·07
10·84
5·150
0·020
1·310
2·490
0·040
34·1
64·8
1·0
Pgbdr, amph-rich porphyritic
medium-grained quartz-diorite.
1264
65·68
18·29
0·05
0·00
0·84
15·50
100·36
12·05
3·950
0·010
0·000
0·300
3·630
0·0
7·6
92·4
61·44
24·51
0·07
6·22
7·62
0·04
99·9
10·90
5·120
0·010
1·180
2·620
0·010
31·0
68·8
0·3
63·07
24·27
0·08
5·59
7·47
0·06
100·54
11·06
5·020
0·010
1·050
2·540
0·010
29·2
70·6
0·3
gabbrodiorite;
63·16
23·98
0·09
5·56
7·91
0·06
100·76
11·08
4·960
0·010
1·040
2·690
0·010
27·8
71·9
0·3
Qtz-dr,
TIEPOLO et al.
AMPHIBOLE IN ARC MAGMA PETROGENESIS
Table 4: Trace element composition (ppm) of brown amphibole in amph-rich porphyritic gabbrodiorite
Sample:
SK16A
SK16A
Li
8·73
9·46
Be
0·59
50·98
B
Na
Sc
Ti
51·05
26246
78·7
14182
2·2
25628
75·3
14101
SK16A
11·4
SK16A
SK16A
8·55
11·0
51·38
1·38
0·72
–
50·98
1·17
3·27
2·52
5·07
3·77
86·2
22253
105
77·3
17468
15017
23586
12·1
SK15A
0·89
24985
6·11
SK15A
50·78
14482
12·3
SK16A
0·59
24489
6·44
SK16A
18445
117
122
18342
18272
20474
79·2
12283
2·05
23658
66·8
14385
V
568
578
612
760
584
759
791
465
472
Cr
964
949
1052
774
1006
696
476
1712
1443
Co
Ni
Zn
Rb
Sr
62·7
178
74·5
3·21
233
63·5
184
61·0
3·34
227
69·1
182
69·0
3·54
221
70·8
67·1
174
171
55·2
64·7
3·09
4·55
234
226
71·9
155
46·6
3·06
229
63·7
167
56·0
3·85
197
57·2
189
55·2
3·21
200
62·1
242
58·5
3·21
227
Y
27·8
26·5
26·4
27·8
25·5
28·6
32·4
24·2
24·2
Zr
31·1
30·1
25·9
29·3
29·3
31·7
36·2
32·9
28·5
Nb
Ba
La
Ce
Pr
Nd
5·60
72·2
3·63
15·4
2·88
15·2
5·59
70·3
3·75
15·1
3·04
15·3
4·36
67·0
3·49
13·8
2·65
14·8
4·40
5·10
74·9
69·3
3·58
3·49
13·7
13·4
2·64
2·67
14·5
14·7
3·90
69·4
3·55
12·9
2·44
14·5
4·34
75·5
4·51
15·1
2·81
15·3
4·79
59·8
4·43
15·3
2·67
14·5
4·65
68·3
3·8
14·4
2·57
15·2
Sm
5·42
4·91
4·66
4·96
4·05
4·54
4·74
4·03
4·32
Eu
1·58
1·38
1·55
1·75
1·55
1·56
1·89
1·274
1·54
Gd
5·30
4·28
5·17
5·75
5·38
5·82
6·49
4·67
5·15
Tb
0·810
0·775
0·880
0·846
0·806
0·827
0·978
0·832
0·768
Dy
5·34
5·18
4·45
5·94
5·66
6·32
6·64
5·28
4·53
Ho
1·01
1·14
1·01
1·09
0·984
1·30
1·27
0·869
0·966
Er
2·50
2·76
2·63
2·76
2·92
3·09
3·17
2·67
2·81
Tm
0·358
0·389
0·399
0·42
0·382
0·37
0·373
0·463
0·362
Yb
2·95
2·33
1·92
2·30
2·11
2·69
2·99
2·27
2·35
Lu
0·342
0·309
0·378
0·412
0·371
0·372
0·396
0·243
0·356
Hf
1·25
1·19
1·03
1·34
1·33
1·48
1·26
1·52
1·30
Ta
0·372
0·304
0·228
0·244
0·313
0·287
0·237
0·300
0·379
Pb
0·706
0·845
1·04
1·28
1·20
1·98
2·88
1·48
1·02
Th
0·116
0·098
0·0391
0·127
0·132
0·168
0·243
0·191
0·13
U
0·0367
0·0535
0·110
0·077
0·102
0·08
0·103
0·175
0·102
The incompatible element patterns (Fig. 9b) reveal enrichment in Th^U relative to LREE and depletion in Ba, Rb,
Nb, Ta, Pb and Zr relative to the neighbouring elements.
Cr contents are high (up to 3198 ppm).
Clinopyroxene in the matrix of the amphibole-rich porphyritic gabbrodiorite has lower Mg# (0·79^0·83), Al2O3
(0·53^1·09 wt %) and TiO2 (0·03^0·13 wt %) contents
than the clinopyroxene inclusions in brown amphibole
(Fig. 8). The chondrite-normalized REE patterns are
characterized by LREE enrichment (LaN/SmN ¼1·1^1·6)
relative to HREE, which are nearly flat at about 2^5
times C1 chondrite (Fig. 9a). Occasionally, a negative Eu
anomaly is also observed (Eu/Eu* down to 0·57). The
REE signature is thus significantly different from that of
the clinopyroxene inclusions in amphibole. A marked
negative anomaly in Ti and depletion in Th and U relative
to the LREE are also peculiar to the incompatible element
pattern of the matrix clinopyroxene (Fig. 9b). Cr contents
1265
JOURNAL OF PETROLOGY
VOLUME 53
NUMBER 6
JUNE 2012
Table 5: Trace element composition (ppm) of green amphibole in amph-rich porphyritic gabbrodiorite
Sample: SK16A
SK16A
SK16A
SK15A
SK15A
SK16A
SK16A
SK16A
SK16A
SK15A
SK15A SK15A
SK15A
SK15A
Position: Rim
Rim
Rim
Rim
Rim
Matrix
Matrix
Matrix
Matrix
Matrix
Matrix
Matrix
Matrix
Li
Be
B
Na
Sc
Ti
8·38
51·01
3·19
8917
75·2
3786
10·0
0·51
2·39
10347
93·3
4529
7·38
50·82
1·30
9835
98·0
5243
7·72
7·30
9·28
12·5
5·83
–
1·88
0·52
0·5
50·79
1·62
9046
63·7
4785
4·26
10611
79·1
5545
50·89
13057
50·87
14194
73·8
4471
1·10
10023
84·9
5305
66·1
4156
13·0
0·86
0·78
18280
92·2
5920
16·5
2·13
2·00
15967
90·9
6073
Matrix
7·99
7·43
15·8
0·79
1·46
–
1·25
9457
57·5
4385
1·02
9164
61·8
5145
1·69
17328
97·8
5326
7·02
51·08
50·86
9225
61·4
4749
V
295
353
503
216
367
310
332
257
382
355
229
247
333
227
Cr
1253
1465
1324
1577
1682
1569
1549
1241
1545
3046
1726
1849
2895
1593
Co
Ni
Zn
Rb
60·0
140
91·0
0·940
58·0
145
87·9
1·29
65·0
182
80·7
1·09
51·7
156
79·4
0·834
57·2
175
73·9
1·461
59·6
151
58·0
135
96·6
87·4
1·023
57·9
138
1·13
73·7
0·500
56·7
129
89·5
1·85
Sr
34·0
30·0
33·3
32·0
25·1
67·0
86·0
45·3
Y
12·4
16·0
12·3
14·0
17·2
16·6
17·6
14·1
18·0
Zr
16·2
17·2
14·2
23·0
20·9
31·0
38·5
24·6
36·4
Nb
Ba
La
Ce
2·36
10·9
5·72
14·5
2·49
17·3
7·26
15·3
2·09
18·2
7·72
17·0
4·40
14·3
9·06
22·7
2·79
3·21
19·9
8·82
20·2
4·83
17·6
23·6
7·24
7·32
23·7
22·8
3·15
12·1
7·03
20·7
26·9
6·89
23·3
0·683
74·5
1·00
81·3
1·57
74·8
0·800
34·4
31·2
16·4
12·9
14·7
16·4
13·5
38·6
23·3
23·2
38·0
25·6
5·45
26·4
7·10
23·7
13·4
8·34
23·2
15·9
8·67
23·8
22·1
6·84
23·2
8·34
23·5
7·36
Sm
1·57
2·22
1·9
2·74
2·89
3·33
3·33
3·32
3·64
3·49
2·57
2·71
2·76
2·59
Eu
0·604
0·653
0·630
0·756
0·684
0·802
0·990
0·800
0·980
0·986
0·674
0·705
0·802
0·590
Gd
2·33
2·57
2·00
2·95
3·18
3·61
3·84
2·39
3·66
3·25
2·78
3·14
3·46
2·12
Tb
0·378
0·484
0·341
0·458
0·543
0·444
0·494
0·375
0·525
0·616
0·489
0·457
0·373
0·382
Dy
2·45
3·02
2·00
2·19
3·01
3·26
3·70
2·71
3·40
4·04
2·61
2·64
3·2
2·32
Ho
0·475
0·638
0·482
0·535
0·601
0·536
0·746
0·516
0·653
0·689
0·572
0·704
0·592
0·372
Er
1·56
2·02
1·66
1·39
1·92
1·68
2·23
1·64
1·63
2·19
1·18
1·59
1·66
1·33
Tm
0·197
0·274
0·225
0·147
0·28
0·27
0·296
0·27
0·27
0·23
0·199
0·259
0·158
0·155
Yb
1·26
1·85
1·16
1·54
1·52
1·88
1·84
2·1
2·06
1·72
1·62
1·12
1·73
1·33
Lu
0·197
0·191
0·174
0·148
0·326
0·244
0·17
0·27
0·313
0·286
0·153
0·231
0·224
0·207
Hf
0·736
0·928
0·900
0·930
0·920
0·816
1·45
1·14
1·34
1·29
0·840
0·830
1·30
0·990
Ta
0·127
0·113
0·0266
0·183
0·08
0·198
0·239
0·213
0·346
0·265
0·290
0·209
0·216
0·212
Pb
0·571
0·708
0·520
0·536
0·872
0·432
0·570
0·304
0·393
0·592
0·490
0·553
0·502
0·605
Th
0·0503
0·105
0·077
0·061
0·154
0·085
0·075
0·079
0·115
0·153
0·083
0·07
0·197
0·055
U
0·0071
0·0414
0·0199
0·0172
0·102
0·0352
0·0464
0·0068
0·049
0·110
0·021
0·0096
0·052 50·0067
are lower (320^1325 ppm) than those of the clinopyroxene
inclusions in amphibole.
Feldspars
Plagioclase in the amphibole-rich porphyritic gabbrodiorite has variable An contents in the range 25^52 mol %.
The K2O contents are between 0·13 and 0·34 wt %. The
chondrite-normalized REE patterns are characterized by
10·6
12·1
3·25
4·59
15·0
1·91
11·9
2·77
5·28
9·02
14·1
2·67
3·92
32·4
1·97
11. 8
3·02
4·20
109
54·0
172
7·67
14·0
3·24
107
81·4
52·5
150
1·66
13·1
2·60
5·01
1·62
50·2
163
Nd
10·5
2·99
3·89
74·1
53·3
165
Pr
11·3
2·38
4·30
109
55·1
165
13·4
2·63
12·2
a marked fractionation between LREE (2^20 times C1
chondrite) and MREE, with LaN/NdN ratios ranging
from 15 to 71 (Fig. 10). HREE are generally below one
times C1 chondrite. Sr and Ba concentrations are in the
range 102^1850 ppm and 2·9^318 ppm, respectively. No significant difference in composition has been observed between plagioclase inclusions in amphibole and plagioclase
in the matrix.
1266
TIEPOLO et al.
AMPHIBOLE IN ARC MAGMA PETROGENESIS
Table 6: Trace element composition (ppm) of green amphibole in medium-grained Qtz-diorite and granodiorite
Sample:
SK14
SK14
SK14
SK14
SK14
SK14
SK11
SK11
SK11
SK11
SK11
Rock type:
Qtz-di
Qtz-di
Qtz-di
Qtz-di
Qtz-di
Qtz-di
Grd
Grd
Grd
Grd
Grd
Li
4·99
7·64
Be
–
–
B
1·79
1·30
Na
Sc
8108
67·5
10244
38·0
8·49
5·65
5·50
8·17
8·44
9·62
8·78
0·84
1·54
51·00
1·01
52·03
3·72
2·72
0·710
2·82
1·57
3·83
3·13
3·29
4·54
4·98
3·88
10583
49·0
35·5
2276
V
201
133
210
144
Cr
760
2032
1897
1046
Ni
Zn
Rb
Sr
50·9
273
39·9
0·488
37·7
56·9
255
42·2
1·19
67·4
2962
9410
Ti
Co
2437
9·83
51·41
57·1
243
47·6
0·795
55·0
2633
57·8
253
45·3
6895
33·4
60·6
134
124
127
8268
7977
7715
136
149
373
257
265
301
258
969
2905
140
60·4
61·5
385
233
45·9
45·3
0·074
0·858
15·0
39·5
10·4
12·7
11·4
11·7
6·9
35·3
35·5
31·6
12·1
29·6
Ba
6·00
La
5·18
Ce
15·0
12·0
7·08
19·2
13·1
6·34
19·0
4·77
13147
145
12·7
3·12
12984
7992
21·0
3·07
13877
158
Y
1·89
12819
7471
Zr
Nb
13900
1617
1443
0·950
60·2
9133
13·0
36·6
54·6
371
2·17
23·4
121
63·0
61·3
83·5
73·0
38·2
38·0
35·0
38·2
54·4
350
1·46
52·3
400
1·81
51·0
318
1·50
58·6
347
1·41
20·7
20·6
20·7
21·2
91·2
81·8
89·0
76·2
30·0
27·0
23·7
27·1
19·3
2·67
1·85
2·21
26·0
19·5
22·1
20·5
21·0
9·48
1·07
8·31
23·8
25·2
25·8
23·0
27·6
5·96
5·09
5·36
22·6
19·4
17·7
23·4
17·0
77·4
78·8
93·2
80·1
16·4
15·9
15·6
102
Pr
1·67
1·92
2·17
2·07
2·04
1·80
19·2
14·8
14·4
17·0
14·4
Nd
8·88
8·07
9·22
9·17
9·14
5·59
96·2
79·9
69·7
83·5
71·6
Sm
1·76
1·74
2·22
2·07
2·29
1·72
29·4
22·7
19·7
23·5
19·0
Eu
0·679
0·645
0·651
0·63
0·668
0·519
Gd
2·63
2·44
2·44
1·69
2·13
1·8
Tb
0·387
0·28
0·401
0·376
0·431
0·207
Dy
2·58
1·84
2·39
2·17
2·01
1·31
Ho
0·513
0·365
0·534
0·426
0·458
0·255
Er
1·7
0·95
1·71
0·769
1·03
0·453
Tm
0·201
0·115
0·168
0·16
0·173
0·147
Yb
1·02
0·900
1·14
1·18
1·45
0·700
Lu
0·234
0·146
0·159
0·144
0·235
0·116
Hf
0·890
1·05
0·940
0·850
0·744
Ta
0·127
0·142
0·173
0·127
Pb
0·503
0·539
0·751
0·354
Th
0·149
0·13
0·198
U
0·084
0·068
0·089
2·89
28·1
4·42
27·6
5·04
2·70
20·9
3·28
19·3
2·92
18·6
2·78
17·5
2·80
22·0
3·04
20·0
2·67
17·5
2·74
15·5
3·32
3·14
3·42
2·75
9·40
7·75
8·74
7·49
1·18
1·18
1·16
1·02
7·75
7·39
8·07
7·26
1·42
1·01
1·02
1·13
0·846
0·589
2·51
1·83
1·32
1·82
1·29
0·171
0·153
1·08
0·750
0·597
0·683
0·535
0·710
0·616
2·05
1·69
2·50
1·78
1·85
0·193
0·130
0·183
0·242
0·172
0·101
0·367
0·119
0·055
0·095
0·097
0·108
0·097
0·099
0·304
0·0603
12·1
1·49
11·3
Qtz-di, medium-grained Qtz-diorite; Grd, granodiorite.
Plagioclase in the medium-grained quartz diorite has
An contents that vary between 27 and 31mol %. The
K2O contents (0·04^0·07 wt %) are significantly lower
than in plagioclase from the matrix of the amphibole-rich
porphyritic gabbrodiorite. The chondrite-normalized
REE patterns (Fig. 10) parallel that of plagioclase from
the amphibole-rich porphyritic gabbrodiorite. These are
characterized by a marked fractionation between La and
Nd (LaN/NdN ¼11·2). La is about 12 times C1 chondrite,
whereas HREE are below one times C1 chondrite. Sr and
Ba concentrations are 1170 ppm and 174 ppm, respectively.
K-feldspar in the matrix of amphibole-rich porphyritic
gabbrodiorite is orthoclase in composition, with Na2O
contents ranging from 0·84 to 1·11wt %.
1267
JOURNAL OF PETROLOGY
VOLUME 53
Table 7: Trace element composition (ppm) of clinopyroxene
in amph-rich porphyritic gabbrodiorite
Sample:
SK16A
SK16A
SK16A
SK15A
SK15A
Li
42·6
31·5
30·9
42·2
46·7
Be
–
B
Na
51·07
3406
Sc
63·8
0·510
50·95
3596
76·4
728
0·640
51·13
2619
61·0
Ti
614
566
V
101
134
100
Cr
416
1325
320
0·820
1·12
2961
58·8
533
88·4
581
50·92
4308
57·8
754
102
780
32·6
30·2
32·5
29·1
30·1
Ni
48·9
69·8
49·1
54·8
66·0
Zn
52·2
39·2
52·5
41·0
Rb
Sr
Y
Zr
0·309
44·2
4·91
12·3
0·071
44·9
5·46
11·3
50·056
44·3
4·97
12·0
50·036
32·3
4·19
10·1
53·8
50·048
44·6
4·77
10·9
Nb
0·0135
0·011
50·022
Ba
0·141
0·589
0·046
0·054
0·048
La
1·90
1·47
2·08
2·31
2·13
Ce
6·37
4·72
6·3
6·91
6·97
Pr
0·986
0·648
0·845
0·707
0·903
Nd
4·14
3·28
3·76
3·39
3·35
Sm
0·980
0·860
0·890
0·910
0·860
Eu
0·365
0·266
0·250
0·214
0·220
Gd
0·640
0·701
0·700
0·800
0·990
Tb
0·124
0·119
0·186
0·099
0·15
Dy
1·04
0·891
1·02
0·792
1·08
Ho
0·163
0·172
0·223
0·142
0·202
Er
0·525
0·665
0·62
0·353
0·519
Tm
0·054
0·0532
0·074
0·058
0·0393
Yb
0·525
0·697
0·46
0·456
0·492
Lu
0·074
0·075
0·094
0·077
0·076
Hf
0·632
0·347
0·473
0·499
0·598
Ta
0·0072
0·0059
–
–
0·0079
Pb
0·375
0·275
0·267
0·498
0·358
Th
0·0347
0·113
0·0185
0·042
0·081
U
0·0187
0·0223
0·0099
50·0109
0·0093
–
JUNE 2012
element patterns (not shown) reveal marked depletions in
Rb, Sr, Pb and Zr^Hf relative to the neighbouring elements. Th and U contents are high (219^434 ppm and
44^99 ppm, respectively).
U ^ P B Z I RC O N G E O C H RO N O L O G Y
Amphibole-rich porphyritic gabbrodiorite
–
Co
NUMBER 6
0·0147
Titanite
Titanite in the matrix and within amphibole in the
amphibole-rich porphyritic gabbrodiorite has comparable
and nearly homogeneous major element compositions.
Trace element contents are variable. The chondritenormalized REE patterns (Fig. 10) are characterized by a
steady decrease from LREE to HREE (LaN/YbN ¼ 6·7^
10·1; YbN ¼ 430^660 times C1). The incompatible trace
Zircon crystals are prismatic with dimensions of about
100^200 mm. Most zircon grains are texturally homogeneous with very weak luminescence; rarely broad banding
or convoluted zoning is observed. In a few zircon grains, a
homogeneous domain at the rim of the crystal with opposite luminescent properties to that of the inner core is
observed. Noticeably, these external zircon domains cut
the broad banding or convoluted zoning of the internal
cores. The boundary between internal and external domains is lobate, providing evidence that the inner zircon
was partially dissolved (Fig. 11).
A total of 71 age determinations were carried out on 30
zircon crystals and the different domains were analysed.
Sixty-five analyses yield concordant U^Pb ages with a
spread between 92 and 127 Ma. Three statistically distinct age clusters are distinguishable in the probability
density diagram (Fig. 12a). The majority of the data are in
the intermediate cluster and give a mean concordia age of
106 3·1 Ma (MSWD ¼ 0·93). A minority of the data fall
within the youngest (97·3 2·7 Ma; MSWD ¼ 0·22) and
the oldest age peaks (123 4·1 Ma; MSWD ¼ 0·52) and
correspond to external and internal zircon domains, respectively (Fig. 11).
The chondrite-normalized REE patterns of zircon
(Fig. 12b) do not reveal significant differences between the
various age clusters. They are characterized by a steady decrease of values (exceeding five orders of magnitude)
from HREE to LREE, coupled with a marked positive Ce
anomaly (Ce/Ce* ¼ 36^108) and a weak negative Eu
anomaly (Eu/Eu* ¼ 0·5^0·99). U and Th contents are variable and range up to 4000 ppm and 7400 ppm,
respectively.
The primary peak at 106 3·1 Ma is considered to be the
most reasonable age for the emplacement of the
amphibole-rich porphyritic gabbrodiorite and is consistent
with the K^Ar amphibole age of 101 5·0 Ma reported
by Karakida et al. (1994) for the Shikanoshima basic
rocks. We attribute the young ages to perturbations of the
U^Pb system induced by the later intrusion of the granitoid dykes, whereas the older age peak at 123 4·1 Ma is interpreted to reflect xenocrystic material inherited by the
mafic melt crystallizing the gabbrodiorite.
Granodiorite
Zircons have prismatic habit, dimensions of about
50^100 mm, and most are characterized by oscillatory
1268
TIEPOLO et al.
AMPHIBOLE IN ARC MAGMA PETROGENESIS
Table 8: Trace element composition (ppm) of plagioclase and titanite
Sample:
SK16A
SK16A
SK16A
SK16A
SK16A
SK15A
SK14
SK16A
SK16A
Rock type:
Pgbdr
Pgbdr
Pgbdr
Pgbdr
Pgbdr
Pgbdr
Qtz-dr
Pgbdr
Pgbdr
Pgbdr
Mineral:
Pl
Pl
Pl
Pl
Pl
Pl
Pl
Ttn
Ttn
Ttn
Li
0·76
50·62
50·40
Be
3·25
5·49
3·83
B
3·23
3·8
Sc
Ti
5·91
35·5
2·57
20·3
52·60
1·93
1·23
–
–
4·67
2·33
50·61
1·59
1·15
55·7
29·1
15·8
50·35
50·57
–
–
–
–
–
52·50
50·53
50·49
50·82
2·02
1·78
49·4
1·82
0·89
50·53
50·29
50·33
Cr
56·53
57·77
56·88
54·14
54·86
Co
0·76
50·147
50·137
0·12
0·21
Ni
3·01
0·44
50·56
50·35
1·18
50·98
Zn
6·49
4·06
6·68
4·52
3·09
51·52
Rb
1·51
1·11
0·83
0·265
0·46
1·08
V
Sr
509
1063
1780
1849
1·13
10·7
0·145
657
1246
1·26
0·41
50·16
SK15A
50·143
4·88
4·57
9·17
–
–
–
50·43
752
1093
1373
58·08
–
–
–
50·135
–
–
–
1·92
–
–
–
3·27
–
–
–
0·165
0·087
31·9
50·097
1171
53·2
36·2
0·133
51·6
Y
0·064
–
0·048
0·07
–
–
50·046
1203
851
Zr
0·128
0·103
–
0·047
0·06
–
50·093
468
380
433
Nb
0·075
50·080
–
–
–
–
–
1285
778
388
Ba
9·13
302·87
318·07
141·95
23·01
280·79
174·18
–
La
3·56
2·4
4·79
3·64
3·44
4·94
2·79
1573
807
903
Ce
2·22
1·14
3·08
3·71
2·18
2·98
2·64
3948
1750
2116
Pr
0·018
0·021
0·215
0·173
0·102
0·173
0·109
451
194
219
Nd
–
–
0·42
0·47
0·3
0·134
0·48
1704
785
795
Sm
–
–
0·155
0·151
–
–
356
189
170
Eu
0·166
0·202
0·229
0·245
0·076
0·489
110
Gd
–
–
0·161
50·079
50·123
50·0218
50·0113
50·041
Tb
–
Dy
–
–
50·095
–
–
50·0236
Ho
Er
50·081
Tm
50·0183
Yb
50·117
Lu
50·0191
Hf
Ta
–
0·039
–
50·0250
–
–
–
50·142
0·344
–
50·16
–
0·026
50·0219
–
50·090
50·0133
0·028
0·034
0·067
0·119
50·209
50·0130
0·027
50·053
0·024
–
–
–
–
0·027
–
0·128
–
50·0302
–
–
9·73
5·28
–
–
0·022
–
–
–
–
Pb
26·1
12·92
Th
–
–
U
–
0·02
50·0177
–
–
–
–
50·148
–
0·023
0·029
50·0247
–
50·063
–
50·0273
–
20·37
13·7
–
50·0276
24·22
–
50·017
285
43·7
272
49·1
126
16·7
108
50·036
53·3
176
28·5
189
75·5
13·4
10·7
83·1
70·7
8·99
99·5
22·4
147
27·5
23·11
435
53·8
152
35·7
11·3
5·27
0·077
96·4
26·1
162
693
148
3·51
312
54·6
8·22
24·0
25·5
2·87
220
43·8
Pgbdr, amph-rich porphyritic gabbrodiorite; Qtz-dr, medium-grained Qtz-diorite.
zoning (Fig. 11). Small apatite inclusions are occasionally
found. Nineteen zircon crystals were analysed and 24 concordant ages were obtained (Fig. 12c). The majority of the
data (14) cluster around a central major peak at 104 3·0
Ma (MSWD ¼ 2·3), which is interpreted as the crystallization age of the granodiorite. These data overlap both the
K^Ar biotite age (98·5 4·9 Ma) obtained by Karakida
et al. (1994) for the Shikanoshima Granodiorite on
Shikanoshima Island and the Rb^Sr whole-rock and mineral isochron age (107·0 0·7 Ma) obtained by Yuhara
et al. (2005a) for a granodioritic body in the Watari
Peninsula (about 19 km NE from Shikanoshima Island).
A few analyses carried out in the cores of the crystals
yield ages that range between 110 and 119 Ma. They are of
1269
JOURNAL OF PETROLOGY
VOLUME 53
NUMBER 6
JUNE 2012
Table 9: U^Pb isotope ratio, apparent and concordant ages of zircons
Run no.
Zrn Position Isotope ratios
no.
Apparent ages
207
Pb/ 1s
206
207
Pb/
206
Pb
238
235
U
Pb/ 1s
U
1s
Concordant age
207
206
Pb/ 1s
207
206
238
U
235
Pb/ 1s
Pb
Pb/ 1s
Age (Ma) 2s
% of disc
U
Sk16, amph-rich porphyritic gabbrodiorite
Ja12a029
27
core
0·0476 0·0023 0·0154 0·0002
0·1011 0·0049
78·4
Ja12a030
28
core
0·0492 0·0036 0·0170 0·0003
0·1153 0·0083
155·9
98·7
1·1
97·8
11·3 108·7
3·8
2·0
110·8
99·3
1·3
99·9
8·6 106·4
1·7
106·6
6·0
Ja12a031
29
core
0·0483 0·0022 0·0155 0·0002
0·1034 0·0046
112·0
5·0
Ja12a032
30
core
0·0484 0·0035 0·0167 0·0003
0·1107 0·0079
118·4
Ja12a033
33
core
0·0479 0·0031 0·0145 0·0002
0·0944 0·0059
93·3
1·3
91·6
Ja12a034
34
core
0·0482 0·0024 0·0151 0·0002
0·1007 0·0049
108·6
Ja12a035
35
core
0·6411 0·0468 0·1091 0·0050
9·6646 0·6281 4604
Ja12a036
37
core
0·0481 0·0024 0·0172 0·0002
0·1142 0·0057
102·2
5·2 109·8
1·5
109·8
5·5 109·8
3
Ja12a037
45
core
0·0484 0·0034 0·0167 0·0003
0·1087 0·0074
119·8
8·4 106·6
2·1
104·8
7·1 106·6
4·1
1·2
Ja12a038
46
core
0·0494 0·0024 0·0152 0·0002
0·1033 0·0051
164·5
8·2
97·1
1·3
99·8
4·9
97·1
2·6
0·3
Ja12a039
46
rim
0·0518 0·0034 0·0154 0·0003
0·1029 0·0063
278·4
18·3
98·5
1·8
99·4
6·0
98·5
3·6
78·9
Ja12a040
49
core
0·0499 0·0022 0·0155 0·0002
0·1070 0·0046
190·3
8·3
99·2
1·1
103·2
4·5
99·2
2·3
79·3
Ja12a041
51
core
0·0485 0·0032 0·0154 0·0003
0·1028 0·0067
121·8
8·0
98·5
1·7
99·4
6·5
98·5
3·4
75·0
Ja12a042
51
rim
0·0491 0·0030 0·0147 0·0002
0·0999 0·0060
153·1
9·3
94·3
1·3
96·6
5·8
94·3
2·6
81·5
Ja12a043
52
core
0·0508 0·0115 0·0161 0·0006
0·1125 0·0251
229·9
52·1 103·2
4·0
108·2
24·1 103·2
7·9
1·5
Ja12a044
54
core
0·0485 0·0031 0·0155 0·0002
0·1033 0·0064
121·3
7·7
99·2
1·3
99·8
6·2
99·2
2·6
1·5
Ja12a045
54
rim
0·0484 0·0023 0·0152 0·0002
0·1015 0·0048
116·4
5·6
97·3
1·1
98·1
4·7
97·3
2·1
2·0
Ja12a046
57
core
0·0607 0·0034 0·0145 0·0002
0·1213 0·0066
629·7
35·1
92·9
1·1
116·2
6·4
Ja22c016
53
rim
0·0476 0·0017 0·0158 0·0002
0·1034 0·0033
78·4
2·7 100·9
1·3
99·9
3·2 100·9
2·6
Ja22c017
53
core
0·0481 0·0014 0·0160 0·0002
0·1061 0·0028
103·7
3·0 102·4
1·2
102·4
2·7 102·4
2·4
0·0
Ja22c018
53
rim
0·0475 0·0014 0·0160 0·0002
0·1046 0·0027
71·9
2·1 102·3
1·2
101·1
2·6 102·3
2·4
1·3
Ja22c019
56
core
0·0487 0·0014 0·0168 0·0002
0·1129 0·0028
134·9
3·8 107·3
1·3
108·6
2·7 107·3
2·6
1·1
Ja22c020
56
core
0·0493 0·0014 0·0162 0·0002
0·1088 0·0028
162·1
4·7 103·7
1·2
104·8
2·7 103·7
2·4
1·1
Ja22c021
56
core
0·0479 0·0015 0·0166 0·0002
0·1095 0·0031
93·8
2·9 105·9
1·4
105·5
3·0 105·9
2·7
0·4
Ja22c022
49
rim
0·0480 0·0014 0·0164 0·0002
0·1084 0·0029
99·3
3·0 104·8
1·3
104·5
2·8 104·8
2·6
0·3
Ja22c023
50
core
0·0476 0·0021 0·0163 0·0002
0·1080 0·0046
77·4
3·5 104·0
1·5
104·1
4·4 104
3
0·1
Ja22c024
46
core
0·0483 0·0014 0·0164 0·0002
0·1089 0·0029
114·0
3·4 104·5
1·3
104·9
2·8 104·6
2·6
0·3
Ja22c025
45
core
0·0485 0·0014 0·0163 0·0002
0·1089 0·0028
122·8
3·6 104·3
1·3
104·9
2·7 104·3
2·5
0·6
Ja22c026
44
core
0·0478 0·0015 0·0161 0·0002
0·1057 0·0030
88·4
2·8 102·7
1·3
102·0
2·9 102·7
2·5
0·7
1·4
5·3
336
92·5
96·9
667
1·1
30
97·4
2403
4·7
98·7
2·3
7·9 108·7
4·0
1·0
4·5
99·3
2·5
0·8
7·6 106·4
3·3
0·0
5·8
92·5
2·6
2·1
4·7
96·9
2·1
156
0·4
1·4
82·8
83·0
21·0
0·9
Ja22c027
44
core
0·0488 0·0018 0·0163 0·0002
0·1097 0·0038
136·3
5·1 104·2
1·5
105·7
3·7 104·2
2·9
Ja22c028
43
rim
0·0482 0·0013 0·0167 0·0002
0·1111 0·0027
111·1
3·1 106·8
1·3
107·0
2·6 106·8
2·6
0·1
Ja22c029
43
rim
0·0480 0·0013 0·0166 0·0002
0·1098 0·0027
100·7
2·8 105·9
1·3
105·7
2·6 105·9
2·6
0·2
0·4
Ja22c030
38
rim
0·0480 0·0014 0·0165 0·0002
0·1087 0·0030
97·3
2·9 105·2
1·4
104·8
2·9 105·2
2·7
Ja22c031
38
rim
0·0483 0·0014 0·0169 0·0002
0·1124 0·0030
115·5
3·4 108·0
1·3
108·1
2·8 108
2·7
0·1
Ja22c032
39
core
0·0481 0·0015 0·0169 0·0002
0·1122 0·0031
101·7
3·1 108·3
1·3
108·0
3·0 108·3
2·7
0·3
Ja22c035
36
core
0·0479 0·0015 0·0168 0·0002
0·1112 0·0031
96·3
2·9 107·5
1·3
107·1
3·0 107·5
2·7
0·4
Ja22c036
33
core
0·0480 0·0015 0·0168 0·0002
0·1113 0·0031
97·8
3·0 107·7
1·4
107·2
3·0 107·6
2·8
0·5
Ja22c037
33
core
0·0482 0·0021 0·0172 0·0002
0·1143 0·0046
108·1
4·7 109·8
1·5
109·9
4·4 109·8
3·1
0·1
Ju03a005
1
rim
0·0471 0·0024 0·0144 0·0002
0·0933 0·0048
51·8
2·7
92·0
1·6
90·5
4·6
92·0
3·1
1·6
Ju03a006
1
core
0·0485 0·0047 0·0199 0·0004
0·1330 0·0126
124·2
11·9 126·8
2·7
126·8
12·0 126·8
5·4
0·0
Ju03a007
1
rim
0·0491 0·0026 0·0173 0·0003
0·1160 0·0060
150·7
7·8 110·3
1·8
111·5
5·8 110·3
3·6
1·0
Ju03a008
2
core
0·0466 0·0021 0·0192 0·0003
0·1228 0·0055
30·3
1·3 122·4
2·0
117·6
5·2 122·3
3·9
4·1
(continued)
1270
TIEPOLO et al.
AMPHIBOLE IN ARC MAGMA PETROGENESIS
Table 9: Continued
Run no.
Zrn Position Isotope ratios
no.
Apparent ages
207
Pb/ 1s
206
207
Pb/
206
Pb
238
235
U
Pb/ 1s
U
207
206
207
206
238
235
Pb/ 1s
1s
Concordant age
Pb
Pb/ 1s
U
Pb/ 1s
Age (Ma) 2s
% of disc
U
Ju03a009
2
rim
0·0483 0·0030 0·0146 0·0003
0·0971 0·0060
114·0
7·1
93·6
1·8
94·0
93·6
3·5
0·4
Ju03a010
3
rim
0·0484 0·0020 0·0184 0·0003
0·1227 0·0050
116·9
4·7 117·5
1·7
117·5
5·8
4·8 117·5
3·5
0·0
Ju03a011
3
rim
0·0483 0·0025 0·0178 0·0003
0·1186 0·0061
115·9
6·0 113·9
1·8
113·8
5·8 113·9
3·5
0·0
Ju03a012
4
rim
0·0483 0·0022 0·0174 0·0003
0·1159 0·0054
111·5
5·2 111·4
1·7
111·3
5·1 111·4
3·4
0·1
Ju03a013
4
rim
0·0475 0·0033 0·0158 0·0003
0·1025 0·0070
71·9
4·9 100·7
1·8
99·1
6·8 100·7
3·6
1·7
Ju03a014
5
core
0·0505 0·0019 0·0160 0·0002
0·1112 0·0043
215·8
8·3 102·5
1·5
107·1
4·1 102·4
3·0
4·3
Ju03a015
5
rim
0·0482 0·0021 0·0197 0·0003
0·1305 0·0057
108·1
4·7 125·6
1·9
124·5
5·5 125·6
3·8
0·9
Ju03a016
6
rim
0·0483 0·0022 0·0161 0·0003
0·1067 0·0048
115·9
5·2 102·8
1·6
102·9
4·6 102·8
3·2
0·1
Ju03a017
6
rim
0·0480 0·0022 0·0175 0·0003
0·1155 0·0052
97·3
4·4 111·8
1·7
110·9
5·0 111·8
3·3
0·8
0·6
Ju03a018
9
core
0·0486 0·0019 0·0169 0·0002
0·1129 0·0044
127·6
4·9 108·0
1·5
108·6
4·2 108·0
3·1
Ju03a019
9
rim
0·0487 0·0022 0·0167 0·0003
0·1118 0·0051
135·3
6·2 106·6
1·6
107·6
4·9 106·6
3·2
0·9
Ju03a020
10
rim
0·0484 0·0023 0·0168 0·0003
0·1113 0·0054
116·4
5·6 107·5
1·7
107·1
5·2 107·5
3·3
0·4
Ju03a021
10
core
0·0476 0·0034 0·0193 0·0003
0·1266 0·0091
80·9
5·8 123·4
2·2
121·1
8·7 123·4
4·4
1·9
Ju03a022
11
core
0·0468 0·0033 0·0197 0·0003
0·1269 0·0089
37·5
2·6 126·0
2·0
121·3
8·5 126·0
4·0
3·8
Ju03a023
11
core
0·0496 0·0028 0·0187 0·0003
0·1274 0·0073
174·9
10·0 119·6
1·9
121·7
7·0 119·6
3·8
1·7
Ju03a024
12
core
0·0482 0·0019 0·0162 0·0002
0·1074 0·0043
111·1
4·4 103·8
1·5
103·5
4·2 103·8
3·0
0·2
Ju03a025
12
core
0·0485 0·0020 0·0162 0·0002
0·1078 0·0044
121·3
4·9 103·7
1·5
104·0
4·2 103·7
3·0
0·3
Ju03a026
13
core
0·0487 0·0021 0·0190 0·0003
0·1256 0·0055
132·0
5·8 121·1
1·9
120·1
5·3 121·1
3·7
0·9
0·6
Ju03a027
13
rim
0·0487 0·0019 0·0162 0·0002
0·1078 0·0043
134·4
5·3 103·3
1·5
103·9
4·1 103·3
2·9
Ju03a029
14
core
0·0488 0·0111 0·0174 0·0006
0·1156 0·0261
138·7
31·6 111·1
4·1
111·1
25·1 111·1
8·1
0·0
Ju03a030
16
core
0·0492 0·0058 0·0194 0·0004
0·1296 0·0153
158·3
18·8 123·9
2·3
123·8
14·6 123·9
4·5
0·1
Ju03a031
16
rim
0·0491 0·0029 0·0200 0·0003
0·1337 0·0079
150·2
8·9 127·3
1·9
127·4
7·5 127·3
3·8
0·1
Ju03a032
16
rim
0·0486 0·0020 0·0172 0·0003
0·1136 0·0046
129·5
5·2 109·9
1·6
109·2
4·4 109·9
3·2
0·6
Ju03a033
17
core
0·0490 0·0020 0·0168 0·0002
0·1122 0·0045
146·4
5·9 107·2
1·5
108·0
4·4 107·2
3·0
0·7
Ju03a034
18
core
0·0493 0·0034 0·0192 0·0004
0·1277 0·0087
160·7
11·0 122·9
2·3
122·0
8·3 122·8
4·5
0·7
Ju03a035
18
rim
0·0499 0·0024 0·0150 0·0002
0·1010 0·0049
190·3
97·7
4·7
96·1
3·1
1·6
0·5
9·2
96·1
1·5
Sk11, granodiorite
Ja12a005
2
core
0·0476 0·0035 0·0149 0·0002
0·0981 0·0072
81·4
6·0
95·5
1·4
95·0
7·0
95·5
2·7
Ja12a006
2
rim
0·0597 0·0032 0·0149 0·0003
0·1229 0·0066
592·4
32·2
95·1
1·6
117·7
6·4
Ja12a008
5
core
0·0485 0·0046 0·0165 0·0004
0·1096 0·0103
123·7
11·8 105·2
2·3
105·6
9·9 105·2
4·6
Ja12a009
5
rim
0·0486 0·0027 0·0161 0·0002
0·1082 0·0059
127·6
7·1 103·2
1·4
104·3
5·7 103·2
2·7
Ja12a010
10
core
0·0482 0·0052 0·0172 0·0003
0·1134 0·0122
107·1
11·7 109·9
2·0
109·1
11·7 109·9
96·1
1·6
96·1
5·8 104·7
9·2
2·1
102·6
6·3
1·1
99·9
8·2
4
0·4
1·0
0·8
96·1
3·1
0·0
9·9 104·7
4·1
2·1
4·6
2·3
Ja12a011
10
rim
0·0482 0·0042 0·0150 0·0002
0·0993 0·0084
107·1
Ja12a012
11
core
0·0472 0·0046 0·0164 0·0003
0·1063 0·0103
59·4
Ja12a013
11
rim
0·0487 0·0023 0·0154 0·0002
0·1034 0·0048
135·3
Ja12a014
18
core
0·4602 0·0298 0·0280 0·0008
1·7733 0·1039 4118
266·5 177·9
5·4 1035
60·7
268·3 277·5
8·2 1631
84·1
98·6
19·2
98·6
1·4
82·8
Ja12a015
18
rim
0·6579 0·0380 0·0440 0·0013
3·9857 0·2054 4641
Ja12a016
19
core
0·0490 0·0038 0·0175 0·0003
0·1180 0·0090
147·4
11·4 111·9
2·1
113·2
8·7 111·9
4·1
1·2
Ja12a017
19
rim
0·0481 0·0021 0·0164 0·0002
0·1084 0·0047
102·2
4·5 104·8
1·3
104·5
4·6 104·8
2·5
0·3
83·0
Ja12a018
25
core
0·7213 0·0520 0·0734 0·0032
7·4015 0·4539 4773
343·9 456·8
19·8 2161
132·5
78·9
Ja12a019
25
rim
0·3701 0·0301 0·0330 0·0013
1·7068 0·1246 3791
308·4 209·3
8·4 1011
73·8
79·3
Ja12a020
27
core
0·8635 0·0689 0·1108 0·0060 13·3735 0·8768 5030
401·2 677·3
36·5 2706
177·4
75·0
Ja12a021
27
rim
0·3505 0·0244 0·0203 0·0007
0·9969 0·0635 3709
257·9 129·8
4·3
702·2
Ja12a022
40
core
0·0487 0·0026 0·0160 0·0002
0·1078 0·0056
7·0 102·4
1·4
104·0
133·4
44·7
5·4 102·4
81·5
2·9
1·5
(continued)
1271
JOURNAL OF PETROLOGY
VOLUME 53
NUMBER 6
JUNE 2012
Table 9: Continued
Run no.
Zrn Position Isotope ratios
no.
Apparent ages
207
Pb/ 1s
206
207
Pb/
206
Pb
238
235
U
Pb/ 1s
U
207
206
Pb/ 1s
207
206
238
U
235
Pb/ 1s
1s
Concordant age
Pb
6·7
Pb/ 1s
Age (Ma) 2s
% of disc
U
Ja12a023
40
rim
0·0485 0·0026 0·0149 0·0002
0·0997 0·0054
123·7
95·1
1·5
96·5
95·1
3·1
Ja12a024
44
core
0·0496 0·0029 0·0161 0·0003
0·1094 0·0063
174·4
10·1 103·2
1·6
105·4
5·2
6·0 103·2
3·2
1·5
2·0
Ja12a025
44
rim
0·0493 0·0029 0·0161 0·0002
0·1065 0·0063
161·6
9·7 103·0
1·4
102·8
6·1 103
2·9
0·2
2·7
0·1
My21b005 46
rim
0·0538 0·0010 0·0162 0·0002
0·1205 0·0022
361·4
6·5 103·8
1·2
115·5
2·1
My21b006 47
rim
0·0482 0·0011 0·0163 0·0002
0·1080 0·0024
107·1
2·4 104·3
1·4
104·2
2·3 104·3
10·1
My21b007 48
core
0·0486 0·0010 0·0186 0·0002
0·1248 0·0027
128·1
2·7 118·8
1·3
119·4
2·5 118·8
2·6
0·5
My21b008 42
rim
0·0487 0·0017 0·0157 0·0002
0·1056 0·0036
131·0
4·5 100·3
1·5
102·0
3·5 100·3
3
1·6
My21b009 45
rim
0·0470 0·0026 0·0161 0·0003
0·1037 0·0056
47·7
2·6 102·6
2·1
100·2
5·4 102·6
4·2
My21b010 39
core
0·0485 0·0013 0·0178 0·0002
0·1189 0·0032
121·3
3·2 113·5
1·4
114·1
3·0 113·5
2·7
0·5
My21b011 38
core
0·0507 0·0012 0·0164 0·0012
0·1148 0·0027
227·2
5·3 104·9
7·5
110·3
2·6 110·8
4·7
4·9
My21b013 34
rim
0·0504 0·0009 0·0172 0·0002
0·1196 0·0021
214·4
3·7 110·0
1·2
114·7
2·0
4·1
My21b014 32
core
0·0547 0·0012 0·0162 0·0002
0·1219 0·0027
399·6
8·9 103·5
1·2
116·8
2·6
11·4
My21b015 30
core
0·0528 0·0011 0·0170 0·0002
0·1234 0·0026
320·6
6·6 108·4
1·2
118·2
2·4
8·3
My21b016 28
rim
0·0494 0·0008 0·0159 0·0002
0·1080 0·0018
167·8
2·8 101·4
1·2
104·1
1·7
2·6
My21b017 29
core
0·0480 0·0013 0·0165 0·0002
0·1093 0·0029
97·8
2·6 105·6
1·3
105·3
2·8 105·6
2·6
My21b018 24
rim
0·0492 0·0008 0·0160 0·0002
0·1087 0·0018
155·0
2·6 102·6
1·2
104·7
1·8 102·6
2·4
2·1
My21b019 22
core
0·0481 0·0009 0·0161 0·0002
0·1070 0·0019
105·7
1·9 103·1
1·2
103·2
1·9 103·1
2·4
0·1
My21b020 21
core
0·0587 0·0016 0·0166 0·0002
0·1335 0·0036
555·6
15·2 106·1
1·5
127·2
3·5
My21b021 16
rim
0·0494 0·0010 0·0163 0·0002
0·1111 0·0023
164·5
3·5 104·4
1·1
107·0
2·2 104·4
My21b022
6
core
0·0558 0·0010 0·0152 0·0002
0·1170 0·0021
442·4
8·0
97·2
1·2
112·4
2·1
My21b023
7
rim
0·0491 0·0017 0·0167 0·0007
0·1106 0·0038
154·5
5·3 106·6
4·4
106·5
3·6 106·5
2·4
0·3
16·6
2·2
2·4
13·5
6·4
0·1
Zircon 02123 for quality control
Ja12a028
0·0536 0·0055 0·0461 0·0010
0·3402 0·0341
352
36
290
7
297
30
290
13
2·4
Ja22c015
0·0523 0·0024 0·0461 0·0007
0·3315 0·0140
297
13
291
4
291
12
291
8
0·0
My21b024
0·0530 0·0013 0·0461 0·0022
0·3368 0·0082
330
8
290
14
295
7
295
12
1·5
Ju03a036
0·0527 0·0037 0·0464 0·0008
0·3345 0·0234
314
22
292
5
293
20
292
9
0·2
Per cent of discordance ¼ [1 – (206Pb/238U/207Pb/235U)] 100.
inherited origin and do not allow a mean concordia
age to be calculated. Five analyses, carried out in the
external portions of the grain, yield a minor peak with a
mean concordia age of 97 3·0 Ma (MSWD ¼ 0·6).
As in the amphibole-rich porphyritic gabbrodiorite,
these ages are interpreted as the result of resetting of the
U^Pb system during the intrusion of the later granitic
dykes.
The chondrite-normalized REE patterns of the zircon
(Fig. 12d) parallel those of zircon in the mafic rocks. The
REE patterns are characterized by a steady decrease from
HREE to LREE and a marked positive Ce anomaly (Ce/
Ce* ¼ 2^313). Unique to zircons from the granodiorite is a
markedly negative Eu anomaly (Eu/Eu* ¼ 0·13^0·48) and
lower Th and U contents: up to 2140 ppm and 1800 ppm,
respectively.
DISCUSSION
Evidence for a primary mineral
assemblage in the mafic rocks
Two mineral assemblages with distinct chemical characteristics, which are not in mutual equilibrium, are recognized
in amphibole-rich porphyritic gabbrodiorites and to a
minor extent in the medium-grained Qtz-diorites: (1)
brown amphibole with clinopyroxene inclusions; (2) green
amphibole with inclusions of the other matrix minerals
(clinopyroxene þ plagioclase). The brown amphibole and
its clinopyroxene inclusions have comparable trace element
signatures and the calculated mean Amph/CpxD values are
close to those expected at equilibrium conditions in basaltic melts at 0·5^2·0 GPa and 1000^10508C (e.g. Adam &
Green, 2003). Brown amphibole and its clinopyroxene
1272
TIEPOLO et al.
AMPHIBOLE IN ARC MAGMA PETROGENESIS
13.00
inclusions are probably on the same liquid line of descent
and represent a primary mineral assemblage crystallized
in a closed system from the same parental liquid.
Green amphibole and clinopyroxene in the amphibolerich porphyritic gabbrodiorite and in the medium-grained
Qtz-diorite have a geochemical signature that is distinct
from the primary minerals. They are characterized by a
marked enrichment in LREE and relatively low HREE
concentrations. The calculated Amph/CpxD values of close
to unity confirm that they are in mutual equilibrium.
Remarkably, the strong LREE enrichment also characterizes plagioclase and titanite. This evidence, as well as the
petrographic relations, suggests that they are also in equilibrium with green amphibole. Green amphibole, clinopyroxene and plagioclase crystallized from the same parental
liquid, which is compositionally distinct from the parental
liquid for the pristine brown amphibole and clinopyroxene.
Al2O3
9.75
6.50
3.25
0
brown amph (gabbrodiorite)
green amph (gabbrodiorite)
green amph (medium-grained Qtz-diorite)
green amph (granodiorite)
0.50
0.60
0.70
0.80
0.90
Mg#
3.00
TiO2
Xenocrystic origin and petrogenetic
affinity of primary minerals
2.25
1.50
0.75
0
0.50
0.60
0.70
0.80
0.90
Mg#
0.80
K2O
0.60
0.40
0.20
0
0.50
0.60
0.70
0.80
0.90
Mg#
Fig. 6. Al2O3, TiO2 and K2O compositional variations vs Mg# of
amphibole. Mg# ¼ Mg/(Mg þ FeTot) in atoms per formula units.
Textural and chemical evidence suggests that the primary
minerals and the matrix minerals are not on the same
liquid line of descent. A closed-system evolution is inconsistent with the sudden transition from brown to green
amphibole (Fig. 4). A more gradual transition between the
two amphiboles would be expected from a melt evolving
by fractional crystallization in a closed system. Green
amphiboles have lower K2O and higher MgO, Cr and occasionally Ni contents than brown amphiboles (Fig. 6).
Given the incompatible behaviour of K2O and the high
compatibility of Cr, Ni and Mg in amphibole (e.g. Adam
& Green, 2006; Tiepolo et al., 2007) the opposite behaviour
would be expected in melts residual after amphibole
crystallization.
A fractional crystallization process driven by amphibole
also cannot account for the trace element variations between brown and green amphiboles. This process was
simulated using Amph/LD values from Tiepolo et al. (2007)
and reported in Table 10. The results reveal that the calculated amphibole compositions in equilibrium with variably
differentiated melts (F ¼ 0·8^0·2) are significantly different
from the analysed compositions of the green amphiboles
(Fig. 13). The relatively flat HREE patterns preclude the
involvement of garnet in the process. According to the
ttn/L
D values reported in the literature (e.g. Tiepolo et al.,
2002), the involvement of titanite also cannot account
for the observed variations. The marked difference in
trace element composition between the brown and green
amphibole also suggests that differentiation processes
other than simple fractionation (e.g. crustal contamination
or magma mixing) cannot account for the observed variations. In particular, the strong HREE depletion in the
green amphibole would imply the addition to the system
of an even more depleted component capable of inducing
the marked dilution, which is unlikely.
1273
JOURNAL OF PETROLOGY
100
Amph/C1
VOLUME 53
NUMBER 6
JUNE 2012
Amph/C1
100
(a)
(b)
10
10
1
brown amphibole
amph-rich porphyritic gabbrodiorite
brown amphibole
amph-rich porphyritic gabbrodiorite
0
1
La Ce Pr NdSm Eu Gd Tb Dy Ho Er TmYb Lu
100
Amph/C1
Li Ba Rb Th U Nb Ta La Ce Sr NdSm Eu Gd Zr Hf Ti Dy Y Yb
Amph/C1
100
green amphibole
amph-rich porphyritic gabbrodiorite(c)
(d)
matrix
matrix
10
10
rim of brown amphibole
rim of brown amphibole
1
green amphibole
amph-rich porphyritic gabbrodiorite
0
1
La Ce Pr NdSm Eu Gd Tb Dy Ho Er TmYb Lu
1000
Amph/C1
green amphibole
Li Ba Rb Th U Nb Ta La Ce Sr NdSm Eu Gd Zr Hf Ti Dy Y Yb
1000
Amph/C1
green amphibole
(e)
Granodiorite
(f)
100
Granodiorite
100
10
1
medium grained Qtz diorite
10
medium grained Qtz diorite
0.1
0.01
1
La Ce Pr NdSm Eu Gd Tb Dy Ho Er TmYb Lu
Li Ba Rb Th U Nb Ta La Ce Sr NdSm Eu Gd Zr Hf Ti Dy Y Yb
Fig. 7. Chondrite-normalized rare earth element and incompatible element patterns for amphibole. Normalization values are from Anders &
Ebihara (1982).
1274
TIEPOLO et al.
AMPHIBOLE IN ARC MAGMA PETROGENESIS
Clinopyroxene
3.00
Al2O3
Included in brown amphibole
in the matrix
2.25
1.50
0.75
0
0.78
0.81
0.83
0.86
0.88
0.86
0.88
Mg#
0.30
TiO2
0.23
0.15
0.08
0
0.78
0.81
0.83
Mg#
Fig. 8. Al2O3 and TiO2 variations vs Mg# of clinopyroxene.
Mg# ¼ Mg/(Mg þ FeTot) in atoms per formula units.
In amphibole-rich porphyritic gabbrodiorites and in
medium-grained Qtz-diorites, the primary minerals were
crystallized from a melt chemically and genetically distinct
from the melt that produced the matrix minerals. The primary minerals can thus be interpreted as being xenocrystic. Textural evidence, such as the oscillatory zoning with
green amphibole, suggests that the brown amphibole has
undergone a melt^rock reaction process. In particular, the
interaction of the brown amphibole with the parental
liquid of the matrix minerals caused partial reaction and
resorption of the primary minerals. The small patches of
brown amphibole in the green amphibole of the
medium-grained Qtz-diorite represent an evolved stage of
this process with almost complete resorption of the primary minerals. In the K2O vs MgO and Sr vs Ba diagrams (Figs 6 and 14), the occurrence of samples with
compositions intermediate to the brown and green amphiboles validates this hypothesis. The xenocrystic origin of
the primary minerals is also supported by U^Pb geochronological data. The U^Pb age spectrum of the
amphibole-rich porphyritic gabbrodiorite reveals the incorporation of xenocrystic zircons at about 123 Ma. The
paucity of 123 Ma zircon in the granodiorite precludes the
possibility that they were assimilated from the host granitoid. The mafic melt, which the matrix minerals crystallized from, probably inherited these zircons from crustal
rocks on its ascent to the level of emplacement. No direct
textural relations between the xenocrystic zircons and the
primary minerals were observed. Nevertheless, the occurrence of xenocrystic primary minerals in the same rocks
in which xenocrystic zircons are observed strongly supports a common origin.
The relatively high Mg# (up to 0·88) and high Cr concentrations (up to 3200 ppm) of the primary clinopyroxene
and brown amphibole suggest their crystallization from a
mantle-derived melt. The basaltic or andesitic nature of
this melt is difficult to assert because pargasitic amphiboles
are stable in both systems (e.g. Tiepolo et al., 2007). The
lack of negative Eu anomalies, as well as the absence of
plagioclase among the primary minerals, suggests that
plagioclase crystallization was suppressed and that the primary minerals crystallized from a primitive mafic
magma. Although shifted slightly towards lower temperature and thus more evolved magma compositions, amphibole is capable of incorporating a broader range of trace
elements than clinopyroxene and therefore the liquid with
which it equilibrated provides more information about the
petrogenetic affinity of the parental melt. The liquid composition was calculated using Amph/LD values for basaltic
systems (Tiepolo et al., 2007; Table 10) and the average
trace element composition of the brown amphibole. The
computed melt shares many similarities with average continental arc basalt compositions (Kelemen et al., 2003;
Fig. 15a). In particular, the two liquids share similar LaN/
YbN ratios and comparable REE, high field strength element (HFSE) and large ion lithophile element (LILE) concentrations. Differences were found in the higher U and
Nb contents and in the lower Sr concentrations of the
melt in equilibrium with the brown amphibole. The computed melt also shares many similarities with the melt in
equilibrium with pargasitic amphibole from the porphyritic gabbros of the Adamello batholith (Tiepolo et al.
2002, 2011).
In conclusion, the brown amphiboles in the amphibolerich porphyritic gabbrodiorites were probably inherited
1275
JOURNAL OF PETROLOGY
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NUMBER 6
JUNE 2012
Clinopyroxene included in brown amphibole
Cpx/C1
100.000
100.0
Cpx/C1
(a)
(b)
10.000
10.0
1.000
1.0
0.100
0.010
0.1
Li K Ba Rb Th U Nb Ta La Ce Sr Pb Nd Sm Eu Gd Zr Hf Ti Dy Y Yb
LaCe Pr NdSmEuGdTbDyHo ErTmYbLu
100.0
Clinopyroxene in the matrix
Cpx/C1
Cpx/C1
100.00
(d)
(c)
10.00
10.0
1.00
1.0
0.10
0.1
LaCe Pr NdSmEuGdTbDyHoErTmYbLu
0.01
Li Ba Rb Th U Nb Ta La Ce Sr Pb Nd Sm Eu Gd Zr Hf Ti Dy Y Yb
Fig. 9. Chondrite-normalized rare earth element and incompatible element patterns for clinopyroxene. Normalization values are from Anders
& Ebihara (1982).
from amphibole-rich ultramafic intrusive rocks (e.g. hornblendites) emplaced about 20 Myr (at about 123 Ma)
before the injection of the mafic melt from which the
matrix minerals crystallized. The occurrence in the Taku
area (about 50 km south of Shikanoshima Island) of
mafic rocks (including hornblendites) with a similar age
(Owada et al., 1999) confirms the presence of diffuse
amphibole-rich ultramafic crustal rocks along this sector
of the continental margin during the Cretaceous. These
ultramafic bodies crystallized from melts with a chemical
affinity close to that of continental arc basalts. Given the
very high Mg# and Cr contents of the clinopyroxene and
brown amphibole, their parental liquid is probably of
mantle origin. According to Tatsumi et al. (2008), arc basalts
could be alternatively produced via anatexis of the amphibolitic crust caused by underplating and/or intrusion of
calc-alkalic basaltic magmas. A crustal origin for the parental liquid of the amphibole-rich ultramafic rocks from
Shikanoshima is unlikely because crustal melts from the
lower basaltic crust have generally significantly lower Mg#
(e.g. Rapp & Watson, 1995; Tatsumi et al., 2008). However,
because the assimilation of ultramafic rocks is capable of
increasing the Mg# in the residual melt (e.g. Tiepolo et al.,
2011), a crustal contribution cannot be excluded.
1276
TIEPOLO et al.
AMPHIBOLE IN ARC MAGMA PETROGENESIS
Plagioclase
100.00
Titanite
Pl/C1
100000
Ttn/C1
porphyritic gabbrodiorite
medium-grained Qtz-diorite
10000
10.00
1000
100
1.00
10
in the matrix
(a)
in green amphibole
(b)
1
0.10
La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er TmYb Lu
La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Fig. 10. Chondrite-normalized rare earth element patterns for plagioclase and titanite. Normalization values are from Anders & Ebihara
(1982).
High-Mg andesite affinity of matrix
minerals
Green amphibole and clinopyroxene in the matrix of
the gabbrodiorite and in the medium-grained Qtz-diorite
have relatively high Mg# values (up to 0·83) and coexist
with plagioclase, suggesting crystallization from a relatively Mg-rich hydrous melt with plagioclase on the liquidus. The occurrence of hornblende (green amphibole)
instead of pargasitic amphibole (brown amphibole) indicates that the parental liquid was Ti-poor and more
SiO2-rich than the melt that crystallized the primary
minerals. Experimental amphiboles in andesitic to dacitic
systems are hornblende rather than pargasitic in composition (e.g. Sisson, 1994; Klein et al., 1997). Moreover,
Ridolfi et al. (2009) has shown that the composition of
amphibole is dependent on the SiO2 content of the melt in
natural systems. Based upon the major element composition of the green amphibole, the equilibrium melt can be
reasonably assumed to be andesitic in composition, and
characterized by relatively high MgO contents; that is,
close to a high Mg-andesite (HMA). The same conclusion
was reached by Yuhara & Uto (2007) on the basis of the
bulk-rock composition of the Shikanoshima Island mafic
rocks.
The average trace element composition of the melt in
equilibrium with the green amphibole was calculated
using the same Amph/LD values (Tiepolo et al., 2007) as for
the melt in equilibrium with the primary brown amphibole
(Table 10). This choice for the S/LD was driven by the uncertainty about the effective SiO2 content of the melt in
equilibrium with the green amphibole. Because Amph/LD
for incompatible elements is positively correlated with the
SiO2 content of the melt, the concentrations of these elements in the model melt should be considered to be a minimum estimate. The melt in equilibrium with the green
amphibole (Fig. 15b) is characterized by relatively high
concentrations of elements with a striking crustal affinity
(Ba, Rb, Pb, Th and U), negative Nb^Ta anomalies, a
marked LREE/HREE fractionation (average LaN/YbN is
about 33) and low HREE concentrations [down to 0·3
times normal mid-ocean ridge basalt (N-MORB)].
Noticeably, the computed melt also has strong negative
anomalies in Sr and Ti and a Sr/Y ratio close to 10. The
low Ti in the computed melt could be an artefact owing to
the excessively high value of the Amph/LDTi used in the calculation. The origin of the low Sr is unclear, but most
probably it is related to plagioclase fractionation that is
stable with the green amphibole.
In conclusion, the matrix minerals appear to have crystallized from a parental liquid similar to an HMA and
with a trace element signature characterized by strong enrichment in elements with high crustal affinity, depletion
in HREE and Sr/Y ratios that suggest a close relationship
with the sanukite-type of HMA.
1277
JOURNAL OF PETROLOGY
VOLUME 53
NUMBER 6
JUNE 2012
(b)
(a)
121.1 ± 3.7 Ma
96.9 ± 2.1 Ma
103.3 ± 2.9 Ma
100 µm
(c)
50 µm
(d)
96.1±3.1 Ma
104.3 ± 2.7 Ma
109.9±4.0 Ma
100 µm
50 µm
Fig. 11. Cathodoluminescence images of representative zircons from the amphibole-rich porphyritic gabbrodiorite (a, b) and granodiorite (c,
d). The location of the spot analyses and U^Pb concordant ages with 2s errors are indicated.
Origin of the green amphibole parental
liquid and its bearing on the origin
of HMA
A primary mantle origin for the parental liquid of the
green amphibole seems unlikely. Nevertheless, the high
MgO content and Mg# of the green amphibole suggests
that it may have crystallized from an almost undifferentiated mantle melt. However, contamination processes at
crustal depths, such as the assimilation of olivine-rich crustal material, have been shown to be capable of buffering
and even increasing the MgO content of residual liquids
(e.g. Tiepolo et al., 2011). No olivine relics were found
in the amphibole-rich porphyritic gabbrodiorites of
Shikanoshima Island, but this does not rule out the possibility that assimilation has occurred earlier in the differentiation process. Furthermore, partial buffering of the
MgO content of the melt, even if less efficient than olivine
assimilation, could also be the result of the assimilation of
brown amphibole and clinopyroxene (i.e. assimilation of
the primary mineral assemblage).
Field and petrographic evidence suggests that the
parental liquid to the green amphibole interacted with the
granodiorite. In particular, the occurrence in the matrix
of the gabbrodiorite and in the medium-grained
Qtz-diorite of minerals typical of granitoid rocks, such as
quartz and K-feldspar, suggests that the parental melt of
the green amphibole has undergone partial hybridization
with the host granodiorite. The same age for mafic and
granitoid rocks is also confirmed by U^Pb geochronology.
Green amphibole is a common mineral in all the studied
lithologies and allows compositional variations in the parental liquid to be monitored from the core of the mafic
complex to the host granodiorite. Al2O3, TiO2 and Mg#
variations reveal that the composition of green amphiboles
from the granodiorite and from the mafic rocks are markedly different and that no interaction between the two
1278
TIEPOLO et al.
AMPHIBOLE IN ARC MAGMA PETROGENESIS
Porphyritic gabbrodiorite
14
12
100000
(a)
10000
Number
10
Zrn/C1
(b)
1000
8
100
6
10
4
1
2
0 .1
0
0 .0 1
L aC eP rN dS mE uG dT bD yH oE rT mY bL u
85 90 95 100 105 110 115 120 125 130 135
Age (Ma)
Granodiorite
9
8
100000
(c)
10000
Zrn/C1
(d)
Number
7
1000
6
5
100
4
10
3
1
2
0.1
1
0.01
0
85 90 95 100 105 110 115 120 125 130 135
L aC eP rN dS mE uG dT bD yH oE rT mY bL u
Age (Ma)
Fig. 12. Age spectra for amphibole-rich porphyritic gabbrodiorite and granodiorite. (a, c) Cumulative probability density plot for U^Pb concordant ages. (b, d) Representative REE compositions of zircons.
parental liquids has apparently occurred. However, the
K2O vs Mg# diagram (Fig. 14a) reveals a mixing line between green amphibole from the mafic rocks and from the
host granodiorite, and suggests that hybridization between
the mafic and granitoid magmas has effectively occurred.
According to the majority of the trace elements, green
amphiboles from the medium-grained Qtz-diorite and
from the matrix of the gabbrodiorite are markedly different from those in the granodiorite. However, a restricted
number of trace elements (Th, U, Sr, Ba and Rb) support
hybridization between the mafic and granitoid melts (e.g.
Figs 6 and 14).
In conclusion, the green amphibole in the mafic rocks
crystallized from a mafic melt of mantle origin that interacted at a deeper level than emplacement with older (up
to 20 Myr) ultramafic material of crustal origin (as suggested by the occurrence of zircons). Whether this interaction is responsible for the high MgO content of the
green amphibole is not clear. This melt subsequently interacted at shallower level with a melt enriched in trace elements with high crustal affinity (K, Sr, Ba, Rb, Th and U).
Given the close relations between the mafic and granitoid
rocks in the field, this melt can be reasonably assumed to
be the host granitoid. Complete magma mixing between
1279
JOURNAL OF PETROLOGY
VOLUME 53
the two end members is unlikely and is not supported by
our data. However, because green amphibole is an early
crystallizing mineral in the matrix of the gabbrodiorite
and in the medium-grained Qtz-diorite we cannot exclude
the possibility that complete magma mixing occurred
Table 10: Experimentally determined amph/liquid partition coefficients used in calculations
Amph/LD
JUNE 2012
during the late stages of the differentiation process. The
late crystallization of quartz, K-feldspar and biotite partially supports this hypothesis.
The mafic rocks of Shikanoshima Island, considered the
intrusive counterparts of sanukite-type HMA, do not
allow the identification of a specific petrogenetic process
for the genesis of this group of HMA. However, the results
of this study favour an origin for sanukite-type HMA not
from primary mantle melts, but with the involvement of
crustal processes and crustal components.
Amph/LD
Li
0·14
Pb
0·12
B
0·01
Nd
0·64
Ba
0·37
Zr
0·45
Rb
0·09
Hf
0·76
Th
0·03
Sm
1·06
U
0·03
Eu
0·96
Nb
0·34
Gd
1·32
Ta
0·32
Ti
2·90
La
0·18
Dy
1·42
Ce
0·30
Y
1·39
Sr
0·62
Yb
1·16
Implications for the role of amphibole in
arc magma petrogenesis
Data source: Tiepolo et al. (2007). Experimental conditions:
T ¼ 10158C; P ¼ 1·4 GPa.
100
NUMBER 6
The occurrence of amphibole-rich mafic rocks similar in
texture to those of Shikanoshima Island and associated
with Cretaceous granitoids has been reported in many
other localities in Japan (e.g. Kunisaki peninsula, Kamei
et al., 2004; Taku area, Oshima, 1961; the Ryoke belt,
Kutsukake, 1974; Nureki et al., 1982; Nakajima et al., 2004;
Abukuma Mountains, Tanaka et al., 1982; Takagi &
Kamei, 2008). Although microchemical investigations are
not available to fully compare these rocks and demonstrate
the xenocrystic origin of the brown amphibole, the striking
similarity to the textural features of the gabbrodiorites of
Shikanoshima Island probably suggests a common origin.
They also reveal that the process that generated the
Amph/C1
F = 0.2
Brown amph
F = 0.4
F = 0.6
F = 0.8
10
Green Amph
1
Ba Rb Th U Nb Ta La Ce Sr Nd Sm Eu Gd Zr Hf Ti Dy Y Yb
Fig. 13. Trace element composition of amphibole in equilibrium with melts variably evolved (F ¼ 0·2^0·8) from the melt in equilibrium with the
brown amphibole. Melt evolution was modelled by closed-system fractional crystallization with amphibole as the sole crystallizing mineral
using the amph/LD values reported in Table 10. The trace element composition of the green amphibole is plotted for comparison.
1280
TIEPOLO et al.
AMPHIBOLE IN ARC MAGMA PETROGENESIS
Ba (ppm)
80
100.0
Liquid in equilibrium with brown amphibole
(a)
liquid/N-MORB
granodiorite
60
40
brown-amph
gabbrodiorite
green-amph
gabbrodiorite
Continental Arc Basalt
1.0
(Kelemen et al., 2003)
0.1
20
Li Ba Rb Th U Nb Ta La Ce Sr Pb Nd Zr Hf Sm Ti Y Yb
green-amph
medium grained qtz-diorite
0
10.0
0
75
150
100.0
225
Liquid in equilibrium with green amphibole
(b)
300
Fig. 14. Sr vs Ba (ppm) variation in green and brown amphibole of
the mafic and granitoid lithologies.
Shikanoshima Island rocks was common during the
Cretaceous along the whole Asian continental margin
now represented by the Japan islands.
Amphibole-rich mafic to ultramafic rocks of variable age
also occur in other orogenic settings worldwide. Examples
are the Tertiary Adamello batholith and the Valmasino
Bregaglia pluton in the Italian Alps (Ulmer et al., 1983;
Blundy & Sparks, 1992; Tiepolo et al., 2003, 2011; Tiepolo
& Tribuzio, 2005), the Husky Ridge complex in the
Cambrian Ross Orogen, North Victoria Land, Antarctica
(Tiepolo & Tribuzio, 2008) and the Torres del Pine in
Patagonia, South America (Leuthold et al., 2009).
Amphibole-rich intrusive rocks with strikingly similar
textural and chemical features thus seem to be present in
most orogenic systems worldwide. They are always found
along major fault systems and associated with granitoid
rocks. Most of these mafic rocks have a porphyritic texture
and are almost indistinguishable at the hand specimen
scale from the gabbrodiorites from Shikanoshima Island.
All these amphibole-rich mafic rocks reveal marked similarities in terms of major element composition of their constituent brown amphiboles (Fig. 16); considering their
different ages and tectonic setting striking similarities are
also observed in their trace element composition (Fig. 17).
In the case of the porphyritic amphibole-gabbros of the
Adamello batholith the same chemical contrast between
the brown amphibole and the green amphibole in the
matrix as in the Shikanoshima Island mafic rocks has
been also observed (Tiepolo & Tribuzio, 2005). These similarities suggest that the amphibole-rich mafic rocks are
liquid/N-MORB
Sr (ppm)
10.0
Continental Arc Basalt
1.0
0.1
(Kelemen et al., 2003)
Li Ba Rb Th U Nb Ta La Ce Sr Pb Nd Zr Hf Sm Ti Y Yb
Fig. 15. Trace element composition of melts in equilibrium with average brown amphibole (a) and green amphibole (b). Amph/LD values
used in the calculation are those of Table 10.
the expression of a magmatic activity with common geochemical affinity that is independent of the age and the
local geodynamic setting and thus related to a specific petrogenetic process. Most of the data obtained for
the brown amphibole from amphibole-rich mafic rocks
worldwide reveal that they crystallized from melts with
a chemical affinity close to that of continental arc
basalts (Tiepolo et al., 2003, 2011; Tiepolo & Tribuzio,
2005, 2008).
Davidson et al. (2007) suggested that, although amphibole is rarely a phenocryst of arc lavas, many intermediate
and silicic magmas in arc settings are residual after cryptic
amphibole crystallization at mid- to lower crustal depths.
Amphibole-rich mafic and ultramafic intrusive rocks
worldwide suggest that they could be the ‘hidden’ amphibole reservoir invoked in the arc crust and in particular
indicate that they may be a common feature of all collisional systems. In this context, amphibole is expected to
play a major role in the differentiation of arc magmas.
The paucity of amphibole-rich ultramafic intrusive
rocks exposed at the Earth’s surface is probably related
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JOURNAL OF PETROLOGY
3.00
VOLUME 53
TiO2 wt%
20.00
2.25
15.50
1.50
11.00
0.75
6.50
0
0.50
0.60
0.70
0.80
0.90
4.00
JUNE 2012
Al2O3 wt%
2.00
0.50
Mg#
NUMBER 6
0.60
Na2O wt%
0.70
0.80
0.90
Mg#
Adamello batholith (Alpine Orogen)
(Tiepolo et al. 2002;
Tiepolo & Tribuzio, 2005; Tiepolo et al., 2011)
3.00
Valmasino Bregaglia (Alpine Orogen)
(Tiepolo et al., 2002)
2.00
Husky Ridge Complex (Ross Orogen)
(Tiepolo & Tribuzio 2008)
1.00
Shikanoshima Island (Japan)
(This work)
0
0.50
0.60
0.70
0.80
0.90
Mg#
Fig. 16. Variation of selected major elements (TiO2, Al2O3, Na2O) vs Mg# for brown amphibole in the Shikanoshima Island mafic rocks and
brown amphiboles in other amphibole-rich intrusive mafic and ultramafic rocks from orogenic settings worldwide. Mg# ¼ Mg/(Mg þ FeTot)
in atoms per formula units.
(2) At about 103 Ma, mafic melts of mantle origin were
produced and were intruded into the arc crust.
During their migration through the arc crust, these
melts interacted with and partially assimilated the
older hornblendites. At the emplacement level, interaction with granitoid liquids occurred and partial hybridization took place.
to the availability of a mechanism capable of exhuming
them from the arc crust, and preserving them. The
mafic magmatic activity frequently associated with granitoid emplacement in collisional settings and the exhumation processes along major faults are probably the most
efficient processes for the sampling and exposure of these
rocks.
S U M M A RY A N D C O N C L U S I O N S
The chemical and geochronological data obtained for the
Shikanoshima Island mafic rocks allow us to construct the
following scenario (Fig. 17).
(1) At about 120 Ma, hydrous melts with a geochemical
affinity close to continental arc basalts were intruded
into the Asian continental margin where they crystallized to form amphibole-rich ultramafic intrusive
rocks (i.e. hornblendites).
The bulk-rock compositions of amphibole-rich porphyritic gabbrodiorites and the medium-grained Qtz-diorites
of Shikanoshima Island are comparable with sanukitetype HMA. The composition of the green amphiboles reflects their crystallization from an andesitic melt characterized by (1) high MgO, (2) strong fractionation of LREE
from HREE, (3) low HREE contents, and (4) high concentrations of elements with a crustal affinity. The parental
liquid for the green amphibole is not a primary mantle
melt but a mantle-derived melt that has assimilated
amphibole-rich ultramafic intrusive rocks and interacted
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TIEPOLO et al.
AMPHIBOLE IN ARC MAGMA PETROGENESIS
La (ppm)
5.00
6.00
3.75
4.50
2.50
3.00
1.25
1.50
0
0
0.300
10
Th (ppm)
20
30
0
40
Y (ppm)
300
0.225
225
0.150
150
0.075
75
0
Nb (ppm)
0
10
Sr (ppm)
20
30
40
30
40
Y (ppm)
0
0
10
20
30
40
0
10
20
Y (ppm)
Y (ppm)
Adamello batholith (Alpine Orogen)
Valmasino Bregaglia (Alpine Orogen)
(Tiepolo et al. 2002;
Tiepolo & Tribuzio, 2005; Tiepolo et al., 2011)
(Tiepolo et al., 2002)
Husky Ridge Complex (Ross Orogen)
Shikanoshima Island (Japan)
(Tiepolo & Tribuzio 2008)
(This work)
Fig. 17. Variation of selected trace elements (Y, La, Nb, Th, Sr) between the composition of the brown amphibole in the Shikanoshima Island
mafic rocks and brown amphiboles in other amphibole-rich intrusive mafic and ultramafic rocks from orogenic settings worldwide.
at the level of emplacement with a melt enriched in elements with a high crustal affinity, which most probably is
the host granitoid. The results of this study suggest that
melts with compositions similar to sanukite-type HMA
can be the result of complex crustal processes involving
both mantle and crustal components.
Our results further suggest that, although amphibole is
rarely a phenocryst in arc lavas owing to its restricted thermal stability, it may play an important role in the differentiation of arc magmas. In particular, we suggest that
amphibole-rich mafic to ultramafic intrusive rocks are
common magmatic products in the arc crust. Their exposure at the Earth’s surface is, however, restricted by the
lack of a mechanism for exhuming these rocks from the
deep arc crust.
AC K N O W L E D G E M E N T S
We are grateful to Andrea Risplendente and Marco
Palenzona for their support during the electron microprobe and LA-ICP-MS analyses, respectively. J. Adam,
R. Rapp and an anonymous reviewer are acknowledged
for the generous comments in manuscript revision. Simon
Turner is acknowledged for the editorial handling.
FU N DI NG
This study was supported by Special Coordination Funds
for Promoting Science and Technology for the Program
for Improvement of the Research Environment for Young
Researchers and Grant-in-Aid for Scientific Research on
Innovation Areas for Geofluids (led by E. Takahashi).
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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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