Sedimentary Geology, 52 (1987) 65-108
65
Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
GEOCHEMICAL
CHARACTERISTICS
ENVIRONMENTS
OF CHERTS
IN THE FRANCISCAN
AND DEPOSITIONAL
AND ASSOCIATED
AND SHIMANTO
ROCKS
TERRANES
KOSHI YAMAMOTO *
Department of Earth Sciences, Nagoya Universi(~, Chikusa, Nagoya 464 (Japan)
(Received November 18, 1985; revised and accepted July 14, 1986)
ABSTRACT
Yamamoto, K., 1987. Geochemical characteristics and depositional environments of cherts and associated rocks in the Franciscan and Shimanto Terranes. Sediment. Geol., 52: 65-108.
Analyses of 122 Jurassic-Cretaceous rock samples from the Franciscan Terrane, California, and 24
Cretaceous samples from the Shimanto Terrane, southwest Japan, show that the cherts and associated
rocks accompanied by pillow basalts are enriched in Fe and Mn which may have been derived from
hydrothermal activities. The results of the fraction analyses for terrigenous, basaltic, hydrothermal, and
biogenic end-members in the Franciscan rocks show that hydrothermal emanations caused iron and
manganese enrichment in the rock samples and played an important role in the formation of siliceous
rocks. Vertical variations of the hydrothermal fraction and TiO2-normalized values for hydrothermal
elements such as Fe, Mn, Ni, Zn, Y and Pb show a possibility that the bedded cherts of the Franciscan
Terrane were deposited in a hydrothermal field on or near some active oceanic ridge, for more than 30
Ma and were a remnant slice of oceanic crust added to the North American continent. On the other
hand, from the field occurrences and vertical variations of TiO2-normalized values of hydrothermal
elements, the Shimanto rocks are inferred to have been deposited in a hemipelagic environment such as
marginal and inter-arc basins.
INTRODUCTION
The origin and the depositional environments
have been widely debated.
Bedded
of bedded cherts in orogenic belts
cherts occur not only lying over ophiolites
( B a r r e t t , 1 9 8 2 ) b u t a l s o i n t e r c a l a t e d i n c l a s t i c r o c k s s u c h as s h a l e s (e.g. A d a c h i ,
1976). S u g i s a k i et al. ( 1 9 8 2 ) e x a m i n e d T r i a s s i c b e d d e d c h e r t s o f t h e l a t t e r t y p e f r o m
t h e M i n o T e r r a n e , c e n t r a l J a p a n , a n d c o n c l u d e d as f o l l o w s ; (1) t h e b e d d e d c h e r t s
are composed mainly of remains of siliceous organisms and contain small amounts
* Present address: Department of Earth Sciences, Kobe University, Nada, Kobe 657, Japan.
0037-0738/87/$03.50
© 1987 Elsevier Science Publishers B.V.
66
of detrital materials; and (2) the cherts were deposited in a hemipelagic environment
such as a continental slope or marginal basin. Barrett (1981) pointed out that the
Jurassic bedded cherts overlying ophiolites in the north Apennines, Italy, contain
SausaLito
!
=m 65
-60
i!i
U.S.A.
i -15
.
120*W
i-
124"W
-10
IF
-5
=~--~ |
z
~=
- (m)
JA
Bedded Chert
-15
10
ot
~/
0
I
130"E
()
300Kin.
|
;40"E
i
t0
-5
grn
-
0 i ~ Shale
~ Chert
--5(m)~ BasaltLimest°ne
Fig. 1. Sampling location (circle) and c o l u m n a r section. Horizontal bar on the left side of the c o l u m n a r
section indicates sampling horizon for shale, and that o n the right for chert and basal Basalt.
67
hydrothermal components and presumably were deposited in a pelagic environment.
The examination of samples recovered by the Deep Sea Drilling Project (DSDP)
demonstrated that metalliferous deposits sometimes occur on ocean-floor basalts
around ocean ridges such as the East Pacific Rise and the Mid-Atlantic Ridge (e.g.
Piper, 1973). These metalliferous deposits are accepted to be formed by hydrothermal activities along active spreading centers. These hydrothermal deposits are
removed from the ocean ridge with the moving oceanic plate and buried under
pelagic clays a n d / o r remains of siliceous organisms (e.g. Cronan, 1976). A series of
sediments formed by this process is often compared with bedded cherts accompanied by metalliferous deposits overlying ophiolites in orogenic belts. Some researchers
assumed, on the basis of the geological and petrological similarity of both sediments, that ophiolites are obducted fragments of old oceanic crust erupted at an
ocean ridge (e.g. Bonatti et al., 1976). Although the geochemical study of the origin
of ophiolites has mostly been focused on basalts (e.g. Miyashiro, 1973) or metalliferous deposits (e.g. Crerar et al., 1982), the chemical characteristics and depositional
environments of siliceous rocks overlying ophiolites must also be an important key
to the nature and emplacement environment of the ophiolites.
In this study, I have analyzed cherts and shales accompanied by pillow basalts in
the Franciscan Terrane, California, and in the Shimanto Terrane, southwest Japan
(Fig. 1). The geochemical features of the siliceous rocks associated with basalt and
the hydrothermal contribution to their formation are discussed in this paper.
Moreover, the depositional environment of the bedded cherts was examined by
means of chemical comparison of the bedded cherts from the Franciscan Terrane
with marine sediments and hydrothermal deposits of various environments.
The Franciscan and the Shimanto Terranes occur on both sides of the Pacific
Ocean, and the geologic structures of both have often been compared with each
other. Nevertheless, their formation processes and the geochemical characteristics of
cherts in these terranes are still very poorly understood. In this study, I discuss the
formation processes of both terranes on the basis of geochemical data from siliceous
rocks.
SAMPLING LOCATION AND SAMPLE DESCRIPTION
The Franciscan Terrane
The Franciscan Terrane is one of the major geologic units in the California Coast
Ranges of western North America; its geology has been studied extensively by many
workers. According to the current opinion (Blake and Jones, 1974), the Franciscan
assemblage is divided into three north-south-trending belts, namely Coastal, Central,
and Yolla Bolly, which are separated by east-dipping thrust faults. The Coastal belt
is the westernmost unit and is composed mainly of flysch-like graywacke sandstone.
The Central belt is composed primarily of graywacke sandstone, shale, minor
68
amounts of chert and associated basalt, gabbro, and serpentinite. The Yolla Bolly
belt is composed mainly of graywacke and metagraywacke with minor chert and
basalt (e.g. Blake and Jones, 1974).
Cherts and associated rocks were sampled in cuttings along a road to Sausalito,
1.5 km north of the Golden Gate Bridge (Fig. 1) in the Central belt, where red and
pale-green bedded cherts are well exposed. The bedded cherts are observed at two
outcrops, 40 m apart. The lower cherts lie conformably on basalt, are 17 m thick,
and are chocolate brown to reddish brown in color. The upper cherts, 8 m thick, are
not associated with basalt and are pale green in color. Chert layers are generally
from 2 to 10 cm thick and average about 5 cm; the shale interlayers are generally
much thinner and average less than 1 cm. Eighty-eight chert, 28 shale partings, and
6 underlying basalt samples were collected from these outcrops.
The basal pillow basalt consists essentially of medium to coarse-grained pyroxene
and plagioclase, with minor amounts of secondary pumpellyite and chlorite. It
shows well-developed ophitic texture. The chert is composed largely of microcrystalline quartz with lesser amounts of hematite and clay minerals, whereas shale parting
is composed mostly of clay minerals, hematite, and microcrystalline quartz. Hematite tends to be more abundantly disseminated in samples of the lower horizons.
Both chert and shale commonly contain varying amounts of radiolarian remains,
but three samples of basal chert (nos. 9-11) contain no radiolarians. These cherts
have an exceptionally large amount of hematite and are veined by megaquartz.
Radiolarian remains are composed mainly of chalcedonic quartz. Chocolate-brown
cherts about 13 m above the basement (nos. 75 and 84) yield radiolarians of the
Lower-Middle Jurassic such as Parahsuum sp. cf. P simplum (Yao, 1982) and
Pachyoncus? sp. On the contrary, pale-green cherts about 60 m above the basement
(nos. 100 and 120) contain Lower Cretaceous radiolarians such as Sethocapsa sp.
and Napora sp. of Pessagno (1977). Radiolarians were identified by H. Yoshida of
the Department of Earth Sciences, Nagoya University.
The Shimanto Terrane
The Shimanto Terrane extends from southern Kanto to southern Kyushu, along
the Pacific coast of southwest Japan. In the Kii Peninsula of southwest Japan, the
Shimanto Terrane can be divided into three belts from north to south, namely, the
Cretaceous Hidakagawa, the Eocene (?) Otonashigawa, and the Oligocene-early
Miocene Muro belts. The Hidakagawa belt is the northernmost unit and is composed mainly of sandstone, shale, alternation of sandstone and shale, and minor
amounts of chert and basalt. The latter two belts are composed largely of flysch-like
alternations of sandstone and mudstone, sandstone, mudstone, and conglomerate
(Nakazawa et al., 1983).
Twelve chert, 7 shale, and 5 basalt samples were collected from the Idani area of
the Hidakagawa Belt, 35 km southeast of Wakayama City (Fig. 1). Chert and shale
69
overlying pillow basalt do not show a bedded structure, but are massive and
intercalate a limestone-basalt layer of 1 m thick.
The basalt is composed mainly of fine-grained plagioclase and pyroxene, and
rarely shows sub-ophitic texture. It also contains minor amounts of secondary
calcite, prehnite, and pumpellyite as veinlets. Calcite pseudomorphs after olivine are
also observed. Chert is chocolate brown and is composed mainly of microcrystalline
quartz, opaque minerals, and clays with a number of radiolarian tests filled with
chalcedony. Shale is composed predominantly of clay minerals, various amounts of
radiolarian remains, and small amounts of opaque minerals. Both chert and shale
are commonly veined by calcite, chlorite, a n d / o r quartz. Although few microfossils
indicating geologic ages are preserved in the Shimanto rocks of this area, Nakazawa
et al. (1983) reported that they were deposited in the Cretaceous.
ANALYTICAL METHOD
Samples were ground into < 120 mesh with an agate mortar. Major and minor
components were analyzed on an automatic X-ray fluorescence spectrometer, JEOL
JSX-100S, according to the method by Sugisaki et al. (1977, 1981). Ferrous iron,
CO2, and H 2 0 were also determined by the method of Sugisaki (1981a). The
analytical results are listed in Appendi~es 1 and 2 for the samples from the
Franciscan Terrane and the Shimanto Terrane, respectively. The analytical data
were recalculated on water, carbonate-, and others-free basis. The recalculated
values are used in the following discussion.
GENERAL CHARACTERISTICSOF CHERT OVERLYING BASALT
Cherts are generally classified into those associated with basalts and those
associated with other rocks. The average chemical compositions of cherts from the
Franciscan and the Shimanto Terranes analyzed in the present work are given in
Table 1, and those from DSDP Leg 32 (Adachi et al., 1986), DSDP Leg 62 (Hein et
al., 1981), and the Mino Terrane, central Japan (Sugisaki et al., 1982) are also listed
for comparison. The first three cherts are resting on basalt and the last two are not.
Chemical compositions other than SiO 2 were used for the comparison, because
the chert is composed predominantly of SiO z. A1203 is most prominent, except for
SiO 2, in the cherts not associated with basalt (the D S D P Leg 62 and the Mino
Terrane), whereas in the cherts resting on basalt (the Franciscan Terrane, the
Shimanto Terrane, and DSDP Leg 32) Fe20 ~ (total iron as Fe203) is twice as high
as A1203, and much MnO is contained. Though the minor-element compositions of
both groups are approximately similar to each other, the cherts associated with
basalt are enriched in Ni, Zn, Y and Pb.
Chemical compositions of the shale closely associated with the chert are important for the examination of the chemical characteristics of the chert (Sugisaki et
70
TABLE 1
Average chemical compositions of cherts from the Franciscan Terrane, the Shimanto Terrane, the D S D P
Leg 62, and the Mino Terrane and of cherts and porcetlanites from the DSDP Leg 32, with their standard
deviations (water-, carbonate-, and others-free basis)
Franciscan
SiO 2
TiO 2
AI203
Fe203*
MnO
MgO
CaO
Na20
K2 O
PzO~
FeO
Fe203
Cr
Co
Ni
Zn
Rb
Sr
Y
Zr
Nb
Mo
Pb
Th
Ba
Ga
No. of
92.63_+
0.09-+
1.41+
2.97-+
0.80-+
0.33_+
0.11-+
0.16±
0.42-+
0.03-+
0.26_+
2.67_+
9.5
3.5
16.0
43.0
9.0
25.0
9.0
27.0
3.3
2.1
25.0
3.3
610.0
1.7
88
Shimanto
2.91
0.05
1.02
1.67
1.17
0.27
0.06
0.19
0.33
0.02
0.13
1.71
_+ 10.0
± 2.4
_+ 16.0
+ 82.0
_+ 9.0
_+ 1.2
± 5.5
+ 12.0
-+ 1.5
+ 1.3
-+ 15.0
+ 2.9
-+620.0
-+ 1+8
92.80_+
0.08 _.%
1.99_+
2.93 +
0,78_+
0.95_+
1.03_+
0.41-+
0.42+
0.11+
0.73_+
2.12±
12.0
6.6
37.0
97+0
16.0
45.0
15.0
17.0
1,7
7.9
13.0
6.4
170.0
3.6
11
DSDP Leg 32
3.14
0.07
1.63
1.42
0.65
0.49
1.06
0.21
0.45
0.13
0.46
1.33
-+ 5.4
-+ 4.2
_+ 14.0
_+ 27.0
_+ 17,0
± 26.0
_+ 10.0
-+ 18.0
± 2.5
-+ 5.7
-+ 17.0
-+ 7,9
_+200.0
_+ 2+5
92.80_+
0.10_+
1.44-+
2.86 -+
0.46-+
0.61+
0.37-+
0.55_+
0.51_+
0.17-+
0,16_+
2.68_+
18.0
8.6
36,0
57.0
21.0
53.0
21,0
28.0
3.7
14+0
13+0
7.0
940,0
4.4
37
3.11
0,07
1,22
1.30
0.29
0.37
0.29
0.14
0.31
0.12
0.04
1.29
_+ 14.0
_+
4.8
_+ 18.0
_+ 32.0
_+ 14.0
_+ 37.0
_+ 13.0
+ 18.0
_+
2.4
-+
4.5
±
6.2
-+ 23.0
_4-1100,0
42.8
D S D P Leg 62
96.14-+0.69
0.04-+ 0.01
0.69-+0.15
0.28 _-4-0.07
0.01-+0.02
0.01-+0.04
0.23-+0.16
0.06_+0.09
0.05 ±0.04
0.03_+0.05
0.07_+0.02
0.20_+0.08
1.0 _+1.0
4.0 _+3.0
3.0 _+2.0
9.0 _+4.0
7
Mino
95.19± 3.46
0.10± 0.10
1.97± 1,35
1.19± 0+59
0.03 -4:0.03
0.53 ± 0.39
0,384 0.08
0.09 4- 0.06
0.51-4~ 0.41
0.06 ± 0.08
0.50± 0.19
0.63 ± 0.38
40+0
3.3
14.0
30.0
29.0
39.0
6.7
23.0
2.7
g.5
8.2
3.3
140.0
3.3
± 22.0
± 2.2
+ 5.4
4:15.0
± 24.0
± 54.0
f 8.4
± 23.0
4~ 1,9
± 1.4
+ 6.0
± 3.1.
± 85.0
± 2.5
71
samples
Elements in ppm; compounds in %.
al., 1982). The average chemical compositions of the shale partings in bedded cherts
in the Franciscan and the Mino Terranes and of massive shales in the Shimanto
Terrane are shown in Table 2. Average shale published by Turekian and Wedepohl
(1961) is also shown in the table.
The shale partings from the Franciscan Terrane have SiO2 contents similar to
that of average shale. However, the SiO2 contents of the shales from the Shimanto
and the Mino Terranes are 6-11% higher than those of the Franciscan shales and
average shale; this is explained by the difference in the chemical composition of
detrital materials contained in them and/or by the addition of SiO2 derived from
71
TABLE 2
Average chemical compositions of shales from the Franciscan, the Shimanto, and the Mino Terrane and
of average shale with their standard deviations (water-, carbonate-, and others-free basis)
Franciscan
SiO 2
TiO 2
AI203
Fe20 ~
MnO
MgO
CaO
Na20
K20
P205
FeO
Fe203
58.95+
1.21+
12.15+
15.82+
2.27+
3.03+
1.59±
0.59+
3.87+
0.14+
1.26+14.69±
Cr
Co
Ni
Zn
Rb
Sr
Y
Zr
Nb
Mo
Pb
Th
Ba
Ga
90.0
18.0
70.0
160.0
110.0
41.0
63.0
180.0
13.0
3.9
78.0
14.0
1800.0
19,0
No. of
samples
Shimanto
9.85
0.90
3.63
7.91
3.07
1.26
3.14
0.99
2.05
0.10
1.68
7.57
+ 110.0
+ 12.0
± 48.0
+ 70.0
4- 62.0
± 23.0
+- 20.0
+- 44.0
+4.4
42.4
+- 85.0
+_ 7.9
+-2100.0
+6.1
69.99±
0.74±
7.76±
9.75+
1.25±
3.13 ±
3.47_+
1.41_+
1.43+
0.25+2.46+7.04_+
25.0
15.0
64.0
160.0
50.0
180.0
41.0
84.0
6.2
4.2
15.0
9.6
260.0
12.0
28
Mino
10.98
0.89
6.95
5.42
1.19
1.99
2.30
1.21
2.13
0.11
2.86
2.56
Shale
63.96_+
0.75_415.97±
6.21+
0.28±
2.47+
0.26_+
0.31+
4.68+
0.27+
2.35+3.62+-
± 22.0
+ 8.3
+ 25.0
+- 30.0
+- 77.0
+-140.0
± 14.0
± 74.0
+ 5.3
+- 4.9
± 11.0
± 12.0
+150.0
_+ 8.1
68,0
17.0
66.0
160.0
210.0
53.0
38.0
164.0
14.0
8.8
29.0
18.0
380.0
25.0
7
7.22
0.21
3.72
2.93
0.70
0.68
0.41
0.41
1.11
0.28
1.37
1.42
+ 30.0
+- 11.0
+ 22.0
_+ 56.0
± 45.0
+ 36.0
+ 23.0
+ 47.0
± 3.4
+_ 3.5
+ 34.0
+ 7.4
+-100.0
+- 6.2
58.19
0.77
15.12
6.75
0.11
2.49
3.09
1.29
3.20
0.12
90.0
19.0
68.0
95.0
140.0
300.0
26.0
160.0
11.0
2.6
20.0
12.0
580.0
19.0
42
Compounds in %; elements in ppm.
r a d i o l a r i a n tests. S h a l e s f r o m t h e F r a n c i s c a n
and the Shimanto Terranes are also
e n r i c h e d i n F e 2 0 ~' a n d M n O , a n d a r e d e p l e t e d i n A 1 2 0 3 . E n r i c h m e n t o f F e 2 0 ~' a n d
MnO,
basalt.
therefore, seems to be an intrinsic character of cherts and shales resting on
The
shales
associated
with
basalt
in
the
Franciscan
Terrane
are
also
characterized by enrichment of Pb and Ba.
Compositions
of the cherts and shales from the Franciscan
and the Shimanto
T e r r a n e s a r e p l o t t e d o n t h e S i O z - A l z O 3 a n d t h e S i O 2 - F e 2 0 ~' d i a g r a m s ( F i g . 2). A s
reference data, samples from several locations--DSDP
and averages of modem
L e g 32, t h e M i n o T e r r a n e ,
argillaceous sediments from various environments
nearshore, marginal, and pelagic--are
plotted.
s u c h as
72
Clear negative correlations between SiO2 and A1203 and between SiO2 and
Fe20 ~ are found on the plots for the cherts and shales from the Mino Terrane,
which are not associated with b a ~ t s . The plots cluster along a line connecting the
points of average marine sediments and that of pure SiO2. This fact and microscopic
observation show that the chert is regarded as a mixture of biogenic S i O 2 and
detrital fragments represented by marine argillaceous sediments (Sugisaki et al.,
1982; Yamamoto, 1983); namely the chert can be considered to be biogenic.
On the other hand, points for the chert and shale resting on basalt (the
Franciscan Terrane, the Shimanto Terrane, and DSDP Leg 32) fall into a field
different from that for the Mino Terrane, and the relations between SiO2 and Al203
and between SiO2 and Fe~O~ are not clear. This might show that detrital materials
contained in the chert and shale on basalt are chemically different from those not
accompanied by basalt. As a source material of the chert and shale on basalt, elastic
materials originating from the underlying basalt should be taken into account; that
is, the siliceous rocks may have been formed by the mixing of basalt-elastics and
biogenic silica. Nevertheless, the data points for the samples resting on basalt
deviate somewhat downward for A1203 and upward for Fe20 ~ from the mixing line
AI203
((1
100
lo
o\
20
0
~0
z0
(%)
\
•
o
.
"x
0
&
\,
A
04
Oo~
o
0
O0 o
0
\,
~,
A
o
\
o
0
o
0
O
o
&
0
ooo%a "
o
o
0
o
/.,0
(%)
o \
73
Fe203
(b
20
100(
~o
0•0.•8
e ~
o~°A°
•
1,~,°O~oCo
•
0
zo
3o ( % )
•
•
0~i A ii A
o
o
80
A 0 0 o°
8°~
60
o
o
00 &
0 0
0 0
00
0 0
0
0
z,,o
('/,)
Fig. 2. Plots of SiO 2 against A1203 and total iron as Fe2Oa(Fe20~). Sample symbols: big solid
circles = Franciscan cherts; big open circles = Franciscan shales; solid triangles = Shimanto cherts; open
triangles = Shimanto shales. Other data points: solid and open squares = cherts and porcellanites from
the DSDP Leg 32 Site 304, respectively (Adachi et al., 1986); small solid and open circles = cherts and
shales from the Mino Terrane, respectively (Yamamoto, 1983); stars = average modern marine sediment
- - 1 = the Nishitsugaru Basin in the Japan Sea, 81 samples (Sugisaki, in press); 2 = the Yanlato Bank in
the Japan Sea, 53 samples (Sugisaki, 1979); 3 = the Japan Trench, DSDP Legs 56 and 57, 53 samples
(Sugisaki, 1980); 4 and 5 = around the Izu-Ogasawara Trench, 45 and 21 samples, respectively (Sugisaki
and Kinoshita, 1981); 6 = the northern Central Pacific Basin, 32 samples (Sugisaki, 1981b); 7 = the
central Pacific transect, Wake to Tahiti, 65 samples (Sugisaki and Kinoshita, 1982). B represents the
average value of basalt (Turekian and Wedepohl, 1961). Regression lines are calculated by the method of
least squares for Mino cherts and shales.
connecting the pure silica with the basaltic composition (Turekian and Wedepohl,
1961). This suggests that these samples were derived not only from biogenic silica
and basalt-clastics, but also from other sources.
HYDROTHERMAL
CONTRIBUTION
TO CHERT AND
SHALE
The most problable source of some elements for these samples resting on basalt is
hydrothermal emanation. Sedimentary rocks overlying basalt are extremely enriched
74
AI
./ \
3
•
Fe
100
1
•
',\
2
"
"
50
1oo
Mn
AI
(b)
,~
No.123,124
No.12~
50
\\
r
o •
/,OO:o O:Oo.
/.
:
•
/£I*." . . . , "
Noo-13a[
~oo
.
.
.
"%..
.
-.
"
~0
•
o Mn
Fe
Fig. 3. A 1 - F e - M n diagram showing the effect of hydrothermal emanations. The concentration of each
corner is not oxide but element. Sample symbols: big solid circles = Franciscan cherts; big open
circles = Franciscan shales: solid triangles = S h i m a m o cherts; open triangles = Shimanto shales. Other
data points: small solid circles = non-hydrothermal cherts and shales from the Mino Terrane (Yamamoto.
1983); s t a r s = a v e r a g e d value of non-hydrothermal modern marine s e d i m e n t s - - / = the Nishitsugaru
Basin in the Japan sea, 81 samples (Sugisaki, in press); 2 = the Yamato Bank in the Japan Sea, 53
samples (Sugisaki, 1979); 3 = the Japan Trench. DSDP Legs 56 and 57. 53 samples (Sugisaki, 1980); 4
and 5 = around the Izu-Ogasawara Trench, 45 and 21 samples, respectively (Sugisald and Kinoshita.
1981); 6 = the northern Central Pacific Basin, 32 samples (Sugisaki, 1981b); 7 = the central Pacific
transect, Wake to Tahiti, 65 samples (Sugisald and Kinoshita, 1982); asterisks = averaged values of
hydrothermal deposits around active ocean ridge l = East Pacific Rise deposit, group b, 9 samples
(Bostr~m and Peterson, 1969); 2 = East Pacific Rise deposit, group a, 5 samples (BosttOm and Peterson.
1969); 3 = East Pacific Rise deposit, 18 samples (Piper, 1973); 4 = nontronites in Galapagos M o u n d s
sediment, D S D P Leg 70, 88 samples (Moorby and Cronan. 1979); 5 = sediment from the T A G field.
75
in Fe20 ~ and MnO (Tables 1 and 2). Adachi et al. (1986) concluded that the DSDP
Leg 32 chert, just on basalt, was derived from hydrothermal fluids. This chert is
composed mainly of hematite (partly more than 50%) and megaquartz containing
many fluid inclusions and is markedly enriched in Fe20 ~" and MnO. Adachi et al.
(1986) named the chert "Hydrothermal Chert", and its chemical characteristics
appear to have affinity with those of the cherts from the Franciscan and the
Shimanto Terranes. The cherts recovered by DSDP Leg 32 are used as reference
d a t a in the following discussion.
The effect of hydrothermal emanation was examined on the A1-Fe-Mn diagram
(Fig. 3), which was proposed by BostriSm and Peterson (1969). Also plotted on this
diagram are hydrothermal deposits around the East Pacific Rise (BostriSm and
Peterson, 1969; Piper, 1973), the Mid-Atlantic Ridge (Shearme et al., 1983), and the
Galapagos Mounds (Moorby and Cronan, 1979).
Points for the cherts and shales from the Mino Terrane and for modern marine
sediments which are free from hydrothermal effects fall into the small Al-rich and
Mn-poor field. Pelagic sediments are generally enriched in hydrogenous elements
such as Mn, Co, and Ni (Sugisaki, 1984) and this enrichment can be attributed to
micro-manganese nodules (Ohashi, 1985). The enrichment of Mn in pelagic sediments, however, is not salient on this figure.
On the other hand, the cherts and shale partings from the Franciscan Terrane,
occupy the field rich in Fe and Mn. Especially the cherts just on the basalt (nos.
9-13) are remarkably enriched in Fe and close to the Fe-apex. As the cherts are
separated vertically from the basalt, the Fe and Mn contents become less. Cherts
from the uppermost horizon (nos. 123, 124, and 126) fall into the same field as that
of the modern marine sediments. Representative hydrothermal deposits from the
East Pacific Rise, the Mid-Atlantic Ridge, and the Galapagos Mounds, which are
interpreted as direct precipitates from hydrothermal solution, are also generally
enriched in Fe and Mn. The Canadian American Seamount Expedition (1985)
found amorphous silica of hydrothermal origin around the Juan de Fuca Ridge. All
these facts show that the cherts and shales from the Franciscan Terrane have been
subjected to hydrothermal activities in relation to the underlying basalt. The same
holds true for the cherts from the Shimanto Terrane.
FRACTION ANALYSES OF THE FRANCISCAN BEDDED CHERTS
In addition to the hydrothermal constituents, the cherts and shales from the
Franciscan and the Shimanto Terranes contain remains of siliceous organisms and
clastic detritus, as mentioned in the sample description. If we regard these three
constituents as end-member components and postulate their chemical compositions,
the fraction of each constituent in each sample can be calculated. Fractions were
analyzed according to the following equation with the least squares method.
76
l
Y'. a(i, j ) . b ( j , k)= c(i, k)
j=l
i = 1 , 2 . . . . . n; k = l , 2 . . . . . m
a(i, j) represents the contribution of the j t h end member in the ith samples,
b(j, k) is the concentration of the kth dement in the j t h end member, and c(i, k)
where
is the concentration of kth dement in the ith sample, n is the number of samples,
m the number of dements and 1 the number of end members.
The chemical composition of each end member was estimated by the following
procedure:
(1) The A1/(AI + Fe + Mn) ratio is an indication of a hydrothermal contribution
to sediments (BostriJm and Peterson, 1969). For example, precipitates from hydrothermal emanations occurring on the East Pacific Rise are characterized by
ratios as low as 0.01 (Bostr~Sm and Peterson, 1969), whereas the average shale
(Turekian and Wedepohl, 1961) and the bedded cherts of the Mino Terrane
(Sugisaki et al., 1982; Yamamoto, 1983) show the ratios of 0.62 and 0.60, respectively. That is, the A1/(AI + Fe + Mn) ratio in sediments decreases with increasing
hydrothermal input to the sediments.
The A1/(AI + Fe + Mn) ratio of the Franciscan bedded cherts increases upward
from the lowest horizon (Fig. 4). This shows that the stratigraphically lower samples
had received an intense hydrothermal input. The basal chert (no. 10) resting just on
the basalt shows a ratio as tow as 0.014, which is close to the value for the
metalliferous deposit on the East Pacific Rise. Microscopic observation shows that
the basal Franciscan chert is composed mainly of hematite and megaquartz and
includes no radiolarian remains. These characteristics are the same as those of the
hydrothermal chert described by Adachi et al. (1986). No. 10 basal chert can be
assumed to be composed exclusively of hydrothermal constituents. Thus, I have
used it as a hydrothermal end-member.
(2) Radiolarians extracted from the recent radiolarian ooze in the central Pacific
comprise nearly pure silica (Yumamoto, 1983). I assumed that the biogenic endmember is pure silica (SiO 2 = 100%).
(3) In order to estimate the composition of the detrital end-member, the
At203/TiO 2 ratio was plotted against the vertical distance from the basal basalt
(Fig. 4). Since the AI203 and TiO2 contents of the hydrothermal end-member are
only 0.20 and 0.014%, respectively, and they are not contained in the biogenic
end-member, the A1203/TIO2 ratio of each sample depends mainly on the composition of elastic detritus in it. If the composition of clastic detritus in each sample is
uniform, the AlzO3/TiO2 ratio does not fluctuate. For example, the AI203/TiO 2
ratio of the bedded cherts from the Mino Terrane does not fluctuate much
stratisxaphieaUy and the average (22.0 + 2.3) is closely similar to the average shale.
This shows invariance of the elastic composition throughout the st ratigraphic
section (Sugisaki et al., 1982). On the contrary, the A1203/TiO 2 ratio of the
77
0
65
0.2
0.~
0.6
Fraction
AL2031Ti02
AII(AI÷FeoMn)
0
10
0
20
1
05
05
I
.o,0
t
O0
° °~
I
O,
im
o,,d~,t,
60
•
~!
60
n m
de~
o
o
/
',n
•
/
•
A,'
/
•
1~
•~
.~.
oa' •
•
/
/
15
/
U
¢-
• olID •
~
o
• . O.~o.
o
Io
oe~e
.
• ;' ~ t
•
10
,'•
o o
| "~e
#
•
Tf °
o~
(m)
J
•
,
0
•
•
•
•
~'~
/
&/ 41L
• E
0
," • • •
7"•: •
•
•
. . . . . 4 -g . . . . . .
h
Fig. 4. Vertical variations of A I / ( A I + Fe + Mn) and Al203//TiO2 ratios for cherts and shales and those
of detrital, biogenic, and hydrothermal fractions for cherts from the Franciscan Terrane. Closed and
open circles represent chert and shale, respectively. The asterisks represent average value of basal basalt.
If an end-member in a sample calculated from the fraction analysis shows a rate less than - 0 . 1 , the
result for the sample is not used. If an end-member shows a rate less than 0 and more than - 0 . 1 , the
content of the end-member is assumed to be 0 and the other two are recalculated. Plotted points of each
fraction are traced by a dotted line, for convenience, and each area divided by the lines represents degree
of the contribution of the end-member.
Franciscan bedded cherts increases upward from the lowest horizon (Fig. 4). The
lowest and the uppermost cherts show ratios of 5 - 1 0 and 20-25, respectively. This
suggests that the composition of clastic detritus in the bedded cherts is not uniform
but varies with the horizon, and the underlying basalt is a possible source of the
clastics. The average shale (Turekian and Wedepohl, 1961) and the Franciscan
underlying basalt have AI2Oa/TiO 2 ratios of 21.9 and 4.0, respectively. The
A1203/TIO2 ratio of the average shale is equivalent to that of chert from the upper
horizon, whereas that of the basalt is equal to that of the lowest horizon. This shows
that clastics in the bedded cherts of the lowest horizon were derived mainly from the
basal basalts and those of the uppermost horizon were from c o m m o n terrigenous
78
materials. Thus, the basaltic detritus and terrigenous materials were added to the
end members for fraction analyses.
The average composition of basal basalts (nos. 1-5) was used as basaltic
end-member and the composition of no. 119 shale (the uppermost shale) was
adopted as terrigenous end-member. This shale shows an A1EO3/TiO 2 ratio of 17.0,
which is a little lower than that of chert from the uppermost horizon. No. 119 shale
lies in a horizon about 70 m above the basal basalt and is inferred to contain no
basaltic detritus. Under the microscope, this shale is composed mainly of clay
minerals and contains no hydrothermal hematite and quartz; detectable radiolarian
remains are few, if any. The hydrogenous constituents were not used for fraction
analyses, because the contribution of hydrogenous component to marine sediments
seems to be small (Fig. 3).
Accordingly, the four end members; hydrothermal, biogenic, basaltic and terrigenous, were employed in fraction analyses. This calculation method is simplified
from that proposed by D y m o n d et al. (1984).
The number of elements, n, in the calculation is 24, involving 10 major and 14
minor elements. The calculated results of fraction analyses are shown for chert alone
in Fig. 4.
Vertical variation of the Al203//TiO2 ratio shows that the basaltic fraction
decreases upward. Since the contributions of the basaltic and terrigenous detritus
are so small, the total of both is shown as detritial fraction in Fig. 4. The vertical
trend of each fraction can be recognized, although each fraction shows a relatively
large fluctuation. Plotted points of each fraction are traced by a dotted line, for
convenience, and each area divided by the lines represents the degree of the
contribution of each end member.
The detrital fraction increases from the lower to the upper horizon. It is at most
0.2 and the clastic detritals played only a minor role in the formation of the cherts.
The biogenic fraction increases remarkably upward. It amounts to 0.4-0.6 in the
lower (from 1 to 5 m above the basalt) compared to 0.8 in the uppermost horizon.
Siliceous organisms played the most important role in the formation of cherts, as a
whole. The cherts more than 60 m above the basal basalt are composed exclusively
of biogenic materials with small amounts of clastic detritus. These cherts appear to
be of the same genesis as those from the Mino Terrane (Suglsaki et al., 1982), which
are not associated with basalt.
The hydrothermal portion amounts to more than 10% within a horizon 16 m
thick from the basal basalt, and it shows marked upward decrease. In the lower
portion of the horizon, the hydrothermal fraction contributes to the chert formation
more significantly than does t h e detrital fraction. The hydrothermal fraction,
although small, is recognized up to the 60 m horizon. 40 m-thick layers between
them are not exposed.
For comparison, fractions were a n a l ~
for the cherts and porceltanites from
D S D P Leg 32 Site 304 and the results are shown in Fig. 5. Analyses of the basal
79
AI/(AI+Fe+Mn)
lod
0.2
o.~
0.6
10
o
o
o
03
ol3
0
O
0
I00
o
O
1
0,5
0.5
20
[3o
80
Fraction
AI203/TiO2
/
•
0
L
80
0
0
J
6O
60
oo
E
• 'LI
oo
rrn
u¢-
D~P~
0
C
o
/
"I0
.9
"7-
/.0
elm
u
it,'
/
•
20
(m)
Fig. 5. Vertical variations of A1/(A1 + Fe + Mn) and A 1 2 0 3 / T i O 2 ratios for the cherts, porcellanites, and
shales and those of detrital, biogenic, and hydrothermal fractions for cherts and porcellanites from the
D S D P L e g 32 Site 304. Solid and open circles, and open squares represent chert, shale, and porcellanite,
respectively. The method of calculation is the same as that used for Fig. 4.
chert and uppermost shale (nos. 56 and 28 in Adachi et al., 1986) and basal basalt
(Marshall, 1973) were used as the hydrothermal, terrigenous, and basaltic end-member, respectively. The number of elements used for the calculation was 16; the
elements are common to the present work and the works by Marshall (1973) and
Adachi et al. (1986). The variation of the hydrothermal fraction for samples from
Site 304 (Fig. 5) is somewhat different from that in the Franciscan cherts; that is,
the hydrothermal fraction decreases upward but increases around the 45 m horizon.
Similarly, the detrital fraction also increases slightly around this horizon but the
A1/(A1 + Fe + Mn) ratio, as an indication of hydrothermal activity, does not change
significantly. These facts suggest that the increase of the hydrothermal fraction
around the 45 m horizon resulted from a relative decrease of biogenic activities. The
hydrothermal fraction in samples from 20 to 90 m above the basal basalt amounts
to about 0.2, suggesting participation in the chert formation.
The cherts from the Shirnanto Terrane show A1/(A1 + Fe + Mn) ratios as large
80
as over 0.09 (Fig. 9), and the hydrothermal end-member cannot be assumed.
Fraction analysis is, therefore, impossible.
CHEMICALCHARACTERISTICSOF HYDROTHERMALCOMPONENT
The fraction analysis shows that the siliceous rocks of the Franciscan Terrane
contain significant amounts of hydrothermal constituents characterized by the
enrichment of Fe and Mn. Various elements other than Fe and Mn may be
concentrated in the hydrothermal components. The characteristics of the hydrothermal components were examined on the basis of the data for the samples within 5 m
from the basal basalt, which were subjected to intense hydrothermal activity.
As shown in Table 3, Fe20 ~ correlates positively with various elements other
than SiO2, CaO, and Na20; on the other hand MnO correlates with those except for
SIO2, CaO, Na20, FeO, Rb, and Sr. Various elements, therefore, seem to behave,
with Fe a n d / o r Mn, as hydrothermal components. On the other hand, SiO2
correlates negatively with almost all elements. On the SiO2-A1203 and the SiO2Fe20 ~' diagrams (Fig. 2), the plotted points of the Franciscan cherts appear to
converge approximately at SiO2 = 100%. The feature is attributed to a process in
which clastics and hydrotherrnal components are mixed with biogenic silica. Accordingly, these apparent correlations between elements may have resulted from the
difference in the mixing ratio.
Thus, the contribution of silica derived from siliceous organisms should be
excluded, and hence the TiO2,normalized values for various elements were used for
this purpose. The TiO2-normalized values are useful indications of the chemical
characteristics and depositional environments of siliceous rocks (Sugisaki, 1984).
With these values we can examine the chemical composition of detrital and
hydrothermal components, excluding the biogenic contribution.
In order to compare sedimentary rocks containing hydrothermal components
with those without the components, averages of TiO2-normalized values for siliceous
rocks from various locations and average shale are listed in Table 4 with their
standard deviations. The TiO2-normalized values for major elements of cherts from
the Mino Terrane and DSDP Leg 62 are similar to those of average shale, except for
the SiO2/TiO: ratio. Since elements other than SiO2 are derived mainly from
clasties (Sugisaki et al., 1982), the elastics in cherts from the Mino Terrane and
DSDP Leg 62 are chemically similar to average shale. As for the TiO2-normalized
values for minor elemonts, the Mino cherts have Cr, Zn, Mo, and Ba values larger
than the average shale.
Compared with the Mino Terrane, the Franciscan cherts and shales have larger
TiO:-normalized values for F~O~', MnO, Ni, Zn, Y, Pb and Ba. Two alternative
explanations may be possible. First, elastics contained in the Franciscan samples
differ chemically from those in the Mino cherts and average shale. Secondly, since
the hydrothermal component is enriched in these elements and depleted in TiO2, the
-0.752
-
MnO
SiO 2
0.740
0.799
- 0.869
F e 2 0 ~'
MnO
SiO 2
Co
-0.961
Fe20 ~
SiO z
0.927
0.729
- 0.865
Ni
- 0.985
0.709
0.937
TiO 2
- 0.553
0.582
0.569
Zn
0.971
0.761
0.890
A1203
- 0.969
0.404
0.924
Rb
0.961
0,567
F e 2 0 ~"
0.131
0.504
- 0.663
Sr
- 0.752
-
0.567
MnO
Y
0.960
0.667
0,879
- 0.959
0,640
0.919
MgO
Zr
0.980
0.859
0.898
0.141
0.364
0.050
CaO
0.772
0.831
0,652
Nb
0.245
-0,185
-0.257
N a 2°
0.650
0.792
0.615
Mo
0,970
0.686
0.918
K 2°
Pb
0.842
0.690
0,793
- 0.878
0.755
0.820
P205
Th
0.721
0.567
0.654
- 0.462
0,029
0.612
FeO
Ba
0.784
0.659
0.669
- 0,964
0.578
1,000
Fe203
0,844
0,555
0.822
- 0,967
0.504
0.903
Ga
Cr
C o r r e l a t i o n coefficients b e t w e e n F e 2 0 ~, M n O , a n d SiO 2 a n d o t h e r c o m p o n e n t s in F r a n c i s c a n c h e r t s a n d shales w i t h i n 5 m f r o m the b a s a l b a s a l t
TABLE 3
82
TABLE 4
TiO2-normalized values for Franciscan cherts and shales within 5 m from the basal basalt, the Mino
cherts, the DSDP Leg 62 cherts, and average shale, with their standard deviations
Franciscan
SiO 2
A1203
Mino
1750.0 _ 1150.0
DSDP Leg 62
1170.0 + 640.0
2790.0 _+530.0
shale
75.0
Fe20 ~
MnO
MgO
CaO
10.0_+
90.0_+
21.0-+
2.6+
2.0-+
3.6
96.0
18.0
2.3
1.4
22.0_+
10.0+_
0.3+
5.9-+
4.7_+
2.3
2.5
0.2
1.3
2.6
19.0_+
7.7-+
0.4_+
0.5-+
7.2_+
2.3
2.9
0.7
1.3
5.7
20.0
8.8
0.1
3.2
4.0
Na20
K20
P205
1.0_+
3.3_+
0.3 -+
2.0
1.7
0.2
1.0-+
5.6_+
0,6 -+
0.5
0.6
0.4
2.0_+
1.4-+
0.9 +
2.7
1.1
1.5
1.7
4.2
0.2
Cr
360
+ 380
380
_+290
Co
Ni
Zn
54
440
2100
+ 51
-+ 270
_+6900
33
160
330
_+ 15
-+ 40
+100
Rb
Sr
Y
Zr
Nb
Mo
Pb
Th
Ba
Ga
43 -+ 58
350 -+ 260
180 + 90
340 _+ 80
52 _+ 40
48 -+ 46
450 _+ 460
33 %
. _+ 43
5600 -+ 3500
12 _+ 17
No. of
27
320 _+ 50
370 +150
34 + 27
220 -+ 20
26 + 14
93 _+ 50
74 _+ 37
28 _+ 36
1400 _+370
35 _4_ 13
71
120
95
-+ 61
36
_+
81
+_ 42
270
_+140
8
25
88
120
180
390
34
210
14
3
26
15
750
25
7
samples
TiO2-normalized values for these elements of Franciscan siliceous rocks are inevitably enhanced.
If an element is abundant in the hydrothermal component, the TiO:-normalized
value of the element correlates with that of Fe20 ~ or MnO; as described earlier, the
hydrothermal component is enriched in Fe and Mn, and the large TiO2-normalized
values of Fe20 ff and MnO result from the contribution of hydrothermal components. As shown in Table 5, the correlation coefficients between Fe20~/TiO 2 and
TiO2-normalized values for SiO2, Cr. Co, Zn, Mo and Pb and those between
MnO/TiO 2 and TiO2-normalized values for Ni, Sr and Y are all greater than 0.Z
Among these elements, the TiO2-norrnalized values for SIO2, Cr, Co, Mo and Sr of
the Franciscan cherts and shales are nearly the same as those of the Mino biogenic
cherts (Table 4); accordingly, it does not necessarily follow that hydrothermal
components are enriched in these elements. On the other hand, the TiO2-normalized
0.871
0.114
0.814
- 0.222
Ni
Co
MnO
-0.294
0.236
AI203
0.740
-0 . 2 15
SiO 2
Fe20~
F e2 0 ~'
MnO
from the basal basalt
0.138
0.740
Zn
-0.312
Fe20 ~
-0.018
- 0.349
Rb
-0.312
MnO
Sr
0.723
0.103
0.225
0.266
MgO
Y
0,797
0.322
0.432
0.191
CaO
0.493
- 0.054
Zr
0.146
0.049
Na20
0.460
0.630
Nb
0.299
0.289
K20
0.089
0.728
Mo
0.223
0.475
P205
0.009
0.738
Pb
0.646
-0.186
FeO
0.069
0.401
Th
1.00
0.313
Fe20.~
0.795
0.140
0,138
0.394
Ba
Cr
-0.217
0.035
Ga
Correlation coefficients between TiO2-normalizcd values for Fe20 ~" and MnO and those for other components in Franciscan cherts and shales within 5 m
TABLE 5
84
25C
o
o
o
o
o
•
o
o•
o
o
•
%
o
o
o
o
o
go
A
•
o
~,^&
•
•
oo
•
8"
j-.
A
•
Z
N
o
o
A
125
o|
%
o
x
o
x
I---
%
o
&
o
•
A
•
oo
•
• •
•°
•
~
A
o•
•
o
o
o
x
x
•
o
2
Q.
•
o&
i o
25
o
.
•
tP
o
Fe20~/Ti02
o
&o
A •
0
%
e0
0
I--
•
o
%
%
•
•
50
~0
MnO/Ti02
,60
Fig. 6. Plots of TiO2-normalized values for Zn, Pb, Ni and Y against Fe20~'/TiO 2 or M n O / T i O 2 ratios.
Sample symbols: solid circles = Franciscan cherts and shales within 5 m from basal basalt; open
circles - Shimanto cherts and shales; triangles = D S D P Leg 32 Site 304 cherts and porcellanites.
values for Zn, Ni, Y and Pb of the Franciscan rocks are much larger than those of
the Mino rocks (Table 4). This suggests that hydrothermal components are enriched
in these four elements. Figure 6 shows the plots of TiO2-normalized values for these
elements against the Fe20~'/TiO 2 or M n O / T i O 2 ratios. For the Franciscan rocks
and D S D P rocks, the TiO2-normali~,exi values for Zn and Pb increase with increasing Fe20~'/TiO 2 ratio. Likewise, the plots showing the Franciscan and Shimanto
rocks show similar trends on the M n O / T i O 2 - N i / T i O 2 and the M n O / T i O 2 - Y / T i O 2
diagrams. These results show that Zn and Pb behave with Fe, while Ni and Y follow
Mn. The P b / T i O 2 ratios of the Shimanto rocks, however, are generally smaller than
those of the Franciscan and D S D P rocks at a certain Fe20~'/TiO 2 ratio. The
TiO2-normalize~ values of Ni and Y of D S D P rocks are generally larger than those
of the others at a certain M n O / T i O 2 ratio. This may be ascribed to some difference
85
in hydrothermal activity such as the E h - p H condition when the hydrothermal
component was deposited from the hydrothermal fluid, as described later.
VERTICAL VARIATION OF TiO2-NORMALIZEDVALUES
The vertical variations of TiO2-normalized values for Fe20~', MnO, Ni, Zn, Y
and Pb are plotted and the variations are compared with that of the hydrothermal
fraction. If the stratigraphic trend of the TiO2-normalized values for these elements
is concordant with that of the hydrothermal fraction, the result of fraction analyses
can be reasonable, and the elements such as Ni, Zn, Y and Pb may behave as
hydrothermal elements.
Vertical variation of the Fe20~'/TiO 2 ratio for the Franciscan bedded cherts
Shows a trend similar to that of the hydrothermal fraction. That is, the largest
Fe20~'/TiO 2 ratio is found in the chert lying immediately on the basalt, and the
ratio decreases upward. Though the TiOE-normalized values for Ni, Zn and Y are
relatively small within 3 m from the basal basalt, each decreases upward from the 3
m-horizon and shows a trend similar to that of the Fe20~'/TiO 2 ratio (Fig. 7). This
shows the possibility that Ni, Zn and Y are contained mainly in an Fe-rich phase
(hematite). The M n O / T i O 2 and P b / T i O 2 ratios do not show such a clear trend as
Fe20~'/TiO 2. The vertical trend of Pb/TiO2, however, is in good accordance with
that of MnO/TiO2, and Pb seems to be concentrated in a Mn-rich phase. These
results are apparently inconsistent with those obtained in the former section. This
may be caused by the difference in the samples used for the discussion. That is,
Franciscan rocks with intense hydrothermal inputs within 5 m from the basal basalt
were used in the former section, whereas in this section all samples were used for the
discussion.
Fractionation between Fe and Mn in hydrothermal deposits is observed in
various regions. According to Toth (1980), the chemical stability limits of oxides of
Fe and Mn indicate that iron will precipitate before manganese in an environment
of increasing p H and oxidation potential, and decreasing temperature, as would be
encountered upon mixing a hydrothermal fluid with oxygenated sea water. The low
TiO2-normalized values for Ni, Zn and Y just upon the basal basalt may also result
from a similar process. The features of TiO2-normalized values show that the
hydrothermal activity had continued up to the horizon 60 m above the basal basalt.
This result is not inconsistent with that of the fraction analysis.
The TiOE-normalized values for Fe20 ~' and Ni of DSDP rocks (Fig. 8) decrease
gradually from the lower to the upper horizon. The hydrothermal fraction from the
fraction analysis shows a distinct increase around 45 m above the basal basalt. This
is ascribed to the relative decrease of organic activity. The TiOE-normalized values
for Fe20~" , MnO, and Ni indicate the gradual and uniform decrease of the
hydrothermal contribution from lower to upper horizon. Though the fractionation
between Fe and Mn is recognized in the lower horizon, the TiO2-normalized values
86
Fe2031Ti02
8 r,
100
MnOITi02
200
50
25
0
N i l T i O 2 xlO 2
5
0
t0
!
6C!$
i
i
K
0
1
I
•
[
m
E
o
.e.-
U
~. o'.-..
t:
<~8==*o
~'o -A, .
o ee
•
o8
0
t'~
• °oo
•
o
p
6e°
•
•
•
~o
ee
O O
lie
~
o
g
~e
%
•
•
(ml
Zn/TiO2xl03
125
65~
Y I T i 0 2 xlO 2
2
250
• •m
PblTiO2xl0 z
5
e~e
•
•
"0"
60
~eb
15
~o
o
;,.,,,.
•
o~
10
•
o"
•
eo
;
8
•
;
;
o e
°
e•
0
-*
oe
•
.
•
ooo
•
"°
o•e
.
eedPo
° Z
"
•
:"
•
o
•
•
•
Fig. 7. Vertical variations of TiO2-normatized values for hydrothermal elements of cherts and shales from
the Franciscan Terrane. Closed and open circles represent chert and shale, respectively.
87
Fe2031Ti02
125
100
MnO/Ti02
lO
250 0
o=o
%
o
oo
oo
m
ol3 8C
o
o
o•
10
o
0
o
n~
Ull
Nil TiO2 xlO 2
5
20
a
ul
o3
E
6C
0=
m•
m
t~
OCD
C
o o o
a
~
U
20
L,-
0
(m)
Z n / T i 0 2 xlO 2
6
100
12
Y I T i 0 2 xlO 3
25
0
o
0
o
o
o
a
oa
o
8c
P b / T i O 2 xlO 2
2
50
o
o
a
o
a
[]
o
m
m
o
o
o
60
o
o
D
OI0
0
D
4c
o~ °
COO
00
0
mi~=o
•
2c
Fig. 8. Vertical variations of TiO2-normalized values for hydrothermal elements of cherts, porcellanites,
and shales from the DSDP Leg 32 Site 304. Closed and open circles, and open squares represent chert,
shale and porcellanite, respectively.
88
AII(AI.Fe*Mn)
20~
0.3
Fe203/Ti02
0.6
0
25
'l"
o
110
15
Nil T i O 2
MnO/TiO2
Ioo
50
0
•
50
0
xlO 2
5
---7
10
o
o
o
o
E
0
e
10
u
o
a
5
e
o
o
o
o
o
o
o
0
0
0
O
Q
g
0
(m)
I
g
g
"
ZnlTiO2xlO
20'
YITiO2 xl0 3
3
25o
125
25
•
o
P b l TiO2 xl0 2
50
0
2
[
4
•
o
•
10
o
5
o
o
o
o
O
8
oo
O
0
0
Fig. 9. Vertical variations of AI/(AI + Fe+ Mn) ratio and TiO2-normalized values for hydrothermal
elements of cherts and shales from the Shimanto Terrane. Closed and open circles represent chert and
shale, respectively.
suggest that the hydrothermal contribution extended to the chert 84 m above the
basalt.
The vortical variation of AI/(A1 + Fe + Mn) ratio and T i O 2 - n o r m ~ e d values in
the sedimentary rocks of the Shimanto Terrane are given in Fig. 9. Scarcely any
vertical trend is found in these ratios. The Shimanto rocks, on the whole, have low
AI/(A1 + Fe + Mn) ratios and high TiO2-normalized values. The ratios of A1/(A1 +
Fe + Mn), Fe20~'/TiO 2, and M n O / T i O 2 are generally in the ranges of 0.1-0.2,
89
40-90, and 15-30, respectively. These ranges are equivalent to those of the Franciscan rocks from 2 to 10 m above the basal basalt. This suggests that the Shimanto
rocks had also received an intense hydrothermal input, although hydrothermal chert
found at D S D P Site 304 and in the Franciscan Terrane was not recognized. In the
horizon about 1 m and 5 - 9 m above the basalt, however, the shales have significantly higher A1/(A1 + Fe + Mn) ratios and lower TiO2-normalized values than the
cherts and shales from other horizons. These low TiO2-normalized values agree with
those of average shale (Table 4). This shows that these shales contain hardly any
hydrothermal constituents. Accordingly, it is inferred that all of the sedimentary
rocks of the Shimanto Terrane were not piled up conformably but had been
disturbed after the sedimentation. This may have resulted from a complex repetition
of strata as discussed later.
ENVIRONMENT OF ERUPTION OF PILLOW BASALTUNDERLYING CHERT
Sedimentary rocks of the Franciscan and the Shimanto Terranes are accompanied by pillow basalt. The environment of eruption of these pillow basalts may give
important information on the depositional environment of the cherts. The T i - Z r - Y
Ti xlO -2 Dpm
Io¢
Z r pprn100
50
100 Y ppm
Fig. 10. Ti-Zr-Y triangular diagram for the basal basalt from the Franciscan and the Shimanto
Terranes. H outlines the Hawaiian tholeiites, O the ocean-floorbasalts, A the andesites and J Japanese
island-arc tholeiites (Pearce and Cann, 1971). Sample symbols: solid circles= basal basalt from the
Franciscan Terrane; open circles= basal basalt from the Shimanto Terrane; open squares = inter-arc
basin basalt published by Ridley et al. (1974).
90
diagram, as a current criterion for the discrimination of the eruption environment of
basalt (Pearce and Cann, 197t), was applied to the present samples (Fig. 10).
Pearce and Cann (1971) distinguished between ocean-floor basalt, Hawaiian
tholeiite, Japanese island-arc tholeiite, and Japanese andesite. The points of the
Franciscan and the Shimanto basalt fall into the area of the ocean-floor basalt field
on the diagram (Fig. 10). The results suggest a possibility that the pillow basalts of
the Franciscan and the Shimanto Terranes had erupted in an environment similar to
that of the recent ocean-ridge and that the hydrothermal component contained in
the sedimentary rocks are derived f r o m the hydrothermal emanations along :an
active spreading center.
DISCUSSION
The examination described above shows that the Franciscan bedded cherts are
chemically akin to the cherts and porcellanites of D S D P Leg 32 Site 304, because
hydrothermal activities are responsible for the rock formation in both areas.
Concentrations of SiO2 in the hydrothermal cherts from the Franciscan Terrane (no.
10) and that of D S D P Leg 32 (no. 56) are 89.9 and 87.9~ (on water- and others-free
basis), respectively. This suggests that relatively large m o u n t s of SiO2 are contained
in the hydrothermal component, and this hydrothermal silica as well as biogenic
silica is embraced in the siliceous rocks. Inorganic precipitates of silica of this sort
are commonly observed as siliceous sinters in hot springs.
The hydrothermal component can be recognized in the chert up to 60 m above
the basal basalt in the Franciscan Terrane. The cherts of this horizon (nos. 100 and
120) yield Lower Cretaceous radiolarians such as Sethocapsa sp. and Napora sp. On
the other-hand, radiolarians indicating the Lower-Middle(?) Jurassic such as
Parahsuum sp. of. P. simplum and Pachyoncus? sp. occur in the cherts about 13 m
above the basalt (nos. 75 and 84). The fossil data show that the bedded cherts of the
Franciscan Terrane were deposited in the hydrothermal field for at least 30 Ma. On
the other hand, at Site 304 the hydrothermal contribution up to the horizon about
85 m above the basal basalt suggests that the cherts and porcellanites deposited
from the Hauterivian/Valanginian to Albian had undergone some hydrothermal
contamination for about 30 Ma (Adachi et al., 1986).
Surface sediments within about 1000 km from the southern part of the East
Pacific Rise are subjected to intense hydrothermal activity (Bostri~m and Peterson.
1969; Leinen and Pisias, 1984). If the spreading rate of the East Pacific Rise in the
past has been the same as that at present (7.9 cm yr-1 calculated by the data of
Minster and Jordan, 1978), the sediments cored at a location 1000 km distant from
the spreading center have been subjected to hydrothermal conditions for more than
13 Ma. Except for the ocean ridge region, such an intense hydrothermal activity o f a
long duration has not been known. Analogically, the sedimentary rocks from the
Franciscan Terrane could have formed in the hydrothermal environment on or near
91
an active ocean ridge. Sedimentary rocks of the DSDP Leg 32 were also inferred to
have been deposited in an environment near the Cretaceous active ridge (the
Japanese spreading center: Lancelot and Larson, 1975; Adachi et al., 1986).
Larson and Chase (1972) assumed that the Farallon Plate was subducted under
the North American Plate about 110 Ma ago. Sediments deposited around the ocean
ridge between the Pacific Plate and the Farallon Plate moved eastward with the
plate motion (Atwater, 1970). This plate motion suggests that the sediments on the
FaraUon Hate were accreted to the North American Plate. The bedded cherts of the
Franciscan Terrane might be a remnant slice of the oceanic crust added to the
North American continent in this manner.
If the above inference is true, the basalt underlying the bedded cherts, an
ophiolite member, is assumed to be an obducted fragment of old oceanic crust
erupted at the ocean ridge.
These results were obtained mainly by chemical comparison between the Franciscan cherts and deep sea cherts. Nevertheless, the occurrences of the cherts of the
Franciscan Terrane and of the DSDP Leg 32 are entirely different from each other.
The former are typical bedded (ribbon) cherts whereas the latter show a lenticular
or nodular shape. Such thick and stratigraphically continuous chert sequences as the
Franciscan bedded cherts have never been reported from the present-day ocean
basin (Jenkyns and Winterer, 1982). This shows that the above deduction for the
environment of formation of ophiolite is not always conclusive. Harper (1980)
suggested that the Josephine ophiolite complex (northwestern California) including
cherts, appears to be one fragment of a complex continental-margin arc, island-arc,
and marginal basin system that developed along part of western North America
during Jurassic time, probably as a response to eastward subduction.
On the other hand, the cherts and shales of the Shimanto Terrane seem to
contain considerable amounts of hydrothermal components, in view of the vertical
variations of the A1/(A1 + Fe + Mn) ratio and the TiOE-normalized values for the
hydrothermal elements. Shales without hydrothermal inputs, however, lie in the
lower horizon near the basal basalt. Moreover, no Shimanto rock in this study
shows an A1/(A1 + Fe ÷ Mn) ratio as low as the 0.01-0.03 observed in the hydrothermal chert from the DSDP Leg 32 Site 304 and the Franciscan Terrane. All
Shimanto rocks show ratios over 0.09. These facts demonstrate that the hydrothermal activity associated with the eruption of the basal basalt in the Shimanto Terrane
was somewhat weaker than in the Franciscan Terrane and in the recent spreading
oceanic ridge. The field occurrence suggests that the stratigraphic relation of the
sedimentary sequences of the Shimanto Terrane is not simple but rather had been
disturbed after sedimentation; perhaps a complex repetition of the strata has
occurred. Relating to this matter, the pillow basalt in the Shimanto Terrane has an
intimate affinity on the T i - Z r - Y diagram (Fig. 10) with ocean-floor basalt erupted
at the ocean ridge. Hawkins (1976), however, has claimed that the basalt occurring
in an inter-arc basin is chemically similar to ocean-ridge basalt; Hart et al. (1972)
92
and Ridley et al. (1974) pointed out the difficulty of chemical discrimination of
inter-arc basin basalt from ocean-ridge basalt. Points on the Ti-Zr-Y diagram (Fig.
10) of inter-arc basin basalt l~ablished by Ridley et al. (1974) fall in the field of
ocean-floor basalt. Thus, the Shimartto basalt is not necessarily akin to the oceanridge basalt but has an affinity with inter-arc basin basalt or marginal-basin basalt.
Furthermore, thick acidic tufts occurring in horizons near those of the present
cherts and shales (Nakazawa et al., 1983) should be taken into account. Thick acidic
tufts intercalated in clastic rocks are generally regarded as products of acidic
volcanism in mobile belts and rarely occur in pelagic sediments. All these lines of
evidence on the $himanto rocks suggest that the cherts and shales had accumulated
in a hemipelagic environment such as a marginal basin and inter-arc basin, where
the basalts had erupted. These results show good agreement with those of Yanai
(1983). Sano (1983) and Miyake (1985) also obtained similar conclusions on the
basis of geological and geochemical data.
Moreover, the limestone layer intercalated in the sequence of cherts and shales of
the Shimanto Terrane shows that the depth of water was probably shallower than
the carbonate compensation depth (CCD).
From the discussion above, the bedded cherts from the Franciscan Terrane are
assumed to have been deposited in a spreading-ridge region. On the other hand, the
Shimanto rocks are inferred to have been deposited in a marginal basin or an
inter-arc basin. Accordingly, it does not necessarily follow that the siliceous rocks
associated with pillow basalt (a member of ophiolite) in the world orogenic belts is
closely akin to the sediments around the spreading oceanic ridge.
ACKNOWLEDGEMENTS
I thank the members of the Department of Earth Sciences, Nagoya University. I
especially wish to express my gratitude to Dr. R. Sugisaki who continually contributed with suggestions and criticism; to Dr. M. Adachi, who gave help and constructive suggestions; to Mr. S. Yogo, who made thin sections for all samples; and to Mr.
H. Yoshida, who identified n~erofossits. I am further indebted to Mrs. K. Taki and
Miss A. Karnijo for their technical assistance. ! also thank Dr. D.L. Jones, U.S.
Geological Survey, for valuable information on the geology of the Franciscan
Terrane.
APPENDIX 1
Analyses of samples from the Franciscan Terrane
Sample no.
1
2
3
4
5
6
9
10
11
13
14
SiO 2
TiO 2
A1203
FeO
48.13
2.97
11.93
5.60
46.17
2.83
11.56
5.11
49.20
2.97
12.04
5.52
49.97
3.00
12.00
5.23
45.37
2.97
11.84
0
45.01
2.96
11,67
1.55
91.43
0.03
0,19
0.20
88,70
0.02
0.18
0.16
89.85
0.02
0.11
0.22
92.08
0.04
0.70
0.15
Fe203
MnO
MgO
CaO
Na20
K20
P205
H/O( - )
H 20( + )
Residuals
10.05
0.26
5.60
8.02
2.83
0,36
0.33
0.65
2.93
0.68
10.23
0.27
4.97
9.17
2.82
0.28
0.32
0.99
3.43
0.35
10.17
0.31
5.43
8.78
2.76
0.26
0.32
0.79
2.96
0.46
10.15
0.54
5.10
7.34
3.00
0,38
0.33
0.70
2.48
0.37
18.34
0.57
5.65
7.80
1.77
0.14
0.28
1.16
3.80
0.14
13.99
1.06
4.50
6.53
1.93
0.31
0.32
3.32
5.61
0,41
6.77
0.03
0
0.05
0
0.02
0
0.19
0.23
0.48
9.22
0.07
0
0.09
0
0.06
0.01
0.23
0.14
1.19
7.10
0.03
0.04
0.07
0.10
0.03
0.01
0.19
0.10
0,69
3.41
0.19
0.48
0.09
0.30
0.13
0.01
0.21
0.75
0.46
Co
Ni
Zn
Rb
Sr
Y
Zr
Nb
Mo
29
24
110
1
58
53
200
8
8
28
24
120
0
63
54
200
7
5
28
22
120
0
67
50
200
7
9
28
25
100
0
110
56
200
7
5
29
23
ii0
0
34
56
2130
6
1
28
54
140
2
30
59
190
11
3
1
4
10
0
5
2
8
3
5
5
7
770
0
9
1
7
2
4
5
3
9
0
9
3
6
3
1
2
13
52
0
9
8
18
3
2
Pb
Th
Ba
Ga
30
9
370
17
0
0
340
21
6
3
360
18
3
4
490
12
6
0
380
24
3
3
780
19
5
0
57
2
53
4
270
0
13
0
170
0
25
0
93
0
50.21
0.64
5.94
1.10
28.31
0.59
2.51
0.06
0
3.84
0.07
1.80
4,40
0.03
7
62
200
100
19
62
120
4
5
79
8
610
9
0.02
0.43
0.62
0.30
P205
H20( - )
H20( + )
Residuals
62.
0
0
0.03
Na20
K20
Ba
Ga
0.15
0.10
MgO
CaO
6
12
3
2
8
0
3.22
0.06
Fe203
MnO
Y
Zr
Nb
Mo
Pb
Th
0,27
0.23
A1203
FeO
1
7
23
0
9
94.83
0.04
SiO2
TiO2
Co
Ni
Zn
Rb
Sr
15
(continued)
Sample no.
APPENDIX 1
170
2
3
9
3
1
6
0
1
7
23
0
9
0
0,45
0.34
0.27
0,02
0.04
0.02
0.08
2.42
0.09
0.18
0.16
94.95
0.04
17
1
0
6
1
12
2
3
9
0
95
0
0
250
1
0
3
14
0.03
0.01
0.28
0.18
0.38
0
0.06
0,00
98.18
0.03
0.00
0.21
1.45
0.04
20
2
9
27
0
8
5
14
5
4
29
0,09
0
0.09
0.01
0.64
0.75
0.20
0.08
0
0.05
0.01
0.65
0.67
0.18
2
18
38
0
7
9
13
5
0
7
0
260
0.05
0.51
0.14
3.41
0.26
0.19
0.04
0.40
0.16
3.65
0.45
0.25
19
93.46
18
93.20
0
30
5
370
3
35
74
1
58
16
24
3
4
0.02
0.13
0.04
0~21
0.03
0,62
1.03
0.76
88.22
0.05
0.67
0.12
4.48
2.98
21
80
150
7
4
48
10
1700
12
13
200
360
81
70
0.03
3.02
0.15
3.94
6.14
0.14
0.0
0.63
7.40
0.22
22.27
7.38
1.72
46.75
22
0
0
0
120
2
23
0
25
3
270
1
22
30
0
27
8
18
1
0.11
0.02
0.39
0,65
0.27
0.05
0.13
0
94.14
0.03
0.36
0.25
2.05
1.42
24
1
45
73
0
43
2O
17
2
0.02
0.59
0.81
1.12
2.55
0.01
0.12
0.29
0.13
91.27
0.05
0.27
0.16
2.43
23
26
340
130
56
75
170
16
6
91
17
1400
14
56
0
32
12
18
0
3
16
3
160
0
25
170
4.91
0.07
3.95
6.33
0.22
7.75
2.91
0.15
0
0.76
9.92
0.17
19.77
42.83
1
4O
0.63
0.12
0.02
0.40
0.74
0.04
0.I2
0.01
0.43
0.15
2.82
1.49
93.58
0.04
25
6
69
110
16
29
27
38
5
1
48
9
480
2
Ni
Zn
Rb
Sr
Y
Zr
Nb
Mo
Pb
Th
Ba
Ga
0.12
1.66
0.25
6.49
3.52
0.55
0.09
0
0.73
0.03
0.88
1.82
0.33
Co
82.40
SiO 2
27
TiO 2
A1203
FeO
Fe203
MnO
MgO
CaO
Na 20
K20
P205
H 200 - )
H20 (+)
Residuals
Sample no.
12
0.48
5.40
0.27
17.90
9.21
1.65
0.12
0
2.82
0.07
2.49
4.58
0.29
54.52
70
54
61
120
11
6
69
1
1100
10
160
240
28
7
38
16
24
0
2
31
0
280
1
39
76
5
0.07
0.93
0.21
3.45
3.48
0.13
0.12
0
0.39
0.02
0.57
1.15
0.33
88.39
29
1
22
13
20
2
5
17
0
220
1
30
62
2
0.05
0.44
0.26
2.41
2.67
0.06
0.08
0
0.21
0.02
0.46
0.68
0.43
92.02
30
8
35
20
31
2
5
32
0
430
1
50
100
5
0.09
0.87
0.35
4.37
4.27
0.32
0.09
0.05
0.43
0.02
0.68
1.35
0.48
85.02
31
0
18
11
22
3
2
21
2
370
1
39
93
3
0.05
0.56
0.25
2.68
1.33
0.11
0.08
0.24
0.10
0.03
0.53
0.93
0.21
92.88
32
8
0.15
2.27
0.17
7.86
4.92
0.30
0.44
0
0.24
0.04
1.41
1.89
0.24
79.89
3
22
48
45
5
3
38
2
1400
5
140
170
33
11
29
17
37
4
3
21
3
680
0
42
75
4
0.12
1.55
0.10
5.58
1.51
0.37
0.12
0.06
0.54
0.02
0.62
1.41
0.65
85.54
34
1
23
12
22
1
3
56
0
690
0
35
80
4
0.06
0.54
0.16
3.90
1.98
0.13
0.36
0.02
0.20
0.04
0.50
1.03
0.58
90.03
35
6
18
10
25
0
2
17
3
300
0
14
41
3
0.07
0.81
0.22
3.67
0.59
0.21
0.07
0.0
0.31
0.02
0.41
0.82
1.64
89.76
36
2
38
3
430
0
9
18
4
3
26
53
1
20
92.19
0.06
0.90
0.26
3.20
0.83
0.09
0.13
0.13
0.15
0.00
0.33
0.79
0.33
37
Co
Ni
Zn
Rb
Sr
Y
Zr
Nb
Mo
Pb
Th
Ba
Ga
SiO 2
TiO 2
A1203
FeO
FezO 3
MnO
MgO
Cao
Na20
K20
P205
H20( - )
H20( + )
Residuals
Sample no.
3
24
44
1
18
12
20
4
2
27
5
460
0
94.17
0.05
0.29
0.35
2.89
0.73
0.21
0.11
0.05
0.13
0.02
0.31
0.:64
0.07
38
4
33
44
0
15
13
18
2
4
15
2
740
0
91.85
0.05
0.65
0.21
2.80
1.25
0
0.16
0.09
0.15
0.02
0.34
0.75
1.15
39
7
26
46
7
25
18
31
3
0
27
9
670
0
89.37
0.10
1.14
0.25
4.03
1.24
0.29
0.09
0.0
0.36
0.03
0.64
0.88
0.52
40
2
14
16
0
17
13
13
2
t
11
0
480
1
93.95
0.04
0.31
0.25
2.24
0~45
0
0.11
0.08
0.07
0.~)2
0.27
0.45
0.39
41
1
8
18
0
18
19
17
2
1
22
3
280
1
96.61
0.04
0.37
0.21
1.56
0.17
0.08
0.0
0.24
0.13
0.02
0.26
0.61
0.27
42
3
12
20
2
25
9
21
2
1
19
2
290
0
92.13
0.06
0.83
0.20
2.42
0.48
0.21
0.09
0.13
0.22
0.02
0.38
0.73
0.21
43
2
10
18
0
24
8
20
3
2
24
4
660
0
93.64
0.05
0.79
0.14
1.74
0.50
0.17
0.09
0.13
0.17
0.02
0.41
0.84
0.37
44
4
10
29
0
20
7
19
2
2
31
2
860
0
90.76
0.05
0.61
0.20
3.62
0,99
0.04
0.07
0.01
0.15
0.02
0.36
0.75
0.62
45
6
12
22
0
21
6
19
2
1
8
3
460
1
92.74
0.05
0.84
0.23
2.38
1,13
0.13
0.12
0.08
0.15
0.01
0.23
0.62
0.68
46
42.25
0.94
11.12
0.05
26.56
2.72
2.83
0.08
0.37
5.20
0.09
1.04
3.88
1.07
19
95
210
130
19
90
210
14
3
76
17
1100
1
47
8
2
130
0
1
6
11
0
24
3
14
1
2
0.62
0.10
0.00
0.24
0,46
0.47
0.11
0,12
0.09
1.42
96.02
0.04
0.49
0.14
48
92.88
0.06
0.77
0.06
2.71
0.46
0.10
0.15
0.10
0.18
0.00
0.21
0.69
0.57
3
11
18
1
27
8
24
2
1
12
1
210
3
Co
Ni
Zn
Rb
Sr
Y
Zr
Nb
Mo
Pb
Th
Ba
Ga
49
SiO 2
TiO2
A1203
FeO
FezO 3
MnO
MgO
CaO
Na20
K20
P205
H20 ( )
H20 ( + )
Residuals
Sample no.
24
8
350
0
2
15
25
8
22
11
30
3
2
91.14
0.08
1.14
0.29
3.93
0.49
0.26
0.07.
0.05
0.47
0.01
0.24
0.89
0.44
50
16
0
240
1
2
6
14
8
17
9
26
2
1
91.99
0.07
0.75
0.19
3.03
0.04
0.25
0.29
0
0.41
0.01
0.21
0.64
0.49
51
68
16
5100
12
37
85
200
130
18
95
150
11
4
46.55
0.67
9.98
0.22
23.39
6.08
2.36
0.07
0
5.04
0.15
0.80
4,80
0,42
52
86.15
0.10
2.06
0.29
5.22
1.61
0.54
0.06
0
0.96
0.05
0.60
1.28
0.60
12
5
1200
1
12
27
55
22
18
25
42
5
1
53
28
18
3600
16
22
80
160
140
15
77
170
14
3
45.96
0.79
10.72
0.13
23.67
3.24
2.66
0.07
0
5.53
0.20
0.78
5.54
0.21
54
8
3
190
2
1
4
6
3
19
5
18
2
2
94.40
0.06
0.67
0.23
1.14
0.02
0.14
0.09
0.04
0.28
0.00
0.16
0.40
0.53
55
64
18
900
19
14
52
130
140
10
79
200
15
2
47.95
0.87
12.35
0.66
21.91
0.64
2.65
0.05
0
5.34
0.11
1.47
4.87
0.11
56
26
4
370
0
3
7
11
0
14
0
16
3
2
95.72
0.04
0.42
0.16
1.54
0.31
0.06
0.06
0.12
0.09
0.02
0.16
0.53
0.75
57
40.62
0.93
10.12
0.25
24.94
8.55
1.98
0.08
0
4.85
0,17
1.00
4.92
1.20
82
28
9900
16
63
120
170
140
52
81
200
15
7
58
1
0
410
3
13
2
2
34
4
9
16
0
16
0
0.05
0.16
0.10
0.02
0.10
4.39
0.55
0.39
0.33
0.05
1.41
92.11
0.04
59
16
53
130
140
14
80
190
13
5
69
16
1400
16
Co
Ni
Zn
Rb
Sr
Y
Zr
Nb
•Mo
Pb
Th
Ba
Ga
0.06
22
4
14
3
1
17
6
270
3
2
5
14
0
0.41
0.21
1.09
4.53
0.38
H~O(- )
H20( + )
Residuals
61
94.96
0.03
0.43
0.15,
1.29
0.09
0.04
0.29
0.06
0.11
0.01
60
(continued)
49.70
0.79
10.47
0.05
22.43
1.09
2.61
0.06
0
5.55
0.10
SiO 2
TiO2
A1203
FeO
Fe203
MnO
MgO
CaO
Na20
K20
P2Os
Sample no.
APPENDIX 1
18
8
21
4
3
15
4
240
1
9
8
18
2
0.17
0.86
0.33
94.85
0.06
0.80
0.14
2.50
0.42
0.07
0.08
0.20
0.27
0.05
62
5
3
8
11
200
2
7
23
24
17
14
41
0.83
0.04
0.29
1.34
0.66
0.27
0.30
0.04
88.85
0.12
2.09
0.51
4.20
0.06
63
17
42
100
150
16
83
230
18
6
38
28
940
21
45.82
0.99
14.56
0.10
18.22
0.81
2.38
0.07
0
5.14
0.20
3.22
6.36
0.19
64
0
3
14
0
17
4
17
3
3
14
5
340
4
0.63
0.52
o.i8
94.83
0.03
0.49
0.15
1.76
0.45
0
0.30
0.07
0.17
0.03
65
56
160
10
5
3O
16
310
13
93
130
11
4
25
0.21
0
5.89
0.08
2.30
4.82
0.78
12.12
1.76
15.68
0.15
2.79
0.07
53.44
66
3
13
10
18
6
24
1
1
12
1
170
1
1
0.30
1.15
0.04
0.08
0.10
0.10
0.48
0.02
0.19
0.45
0.55
94.39
0.06
1.09
67
15
84
230
15
4
45
22
530
21
130
190
5
41
0.04
52.02
0.88
12.97
2.11
12.52
0.18
3.09
0.07
0.15
6.40
0.12
3.03
5.37
68
3
18
6
190
2
2
7
22
21
15
10
29
4
92.10
0.08
1.63
0.54
1.29
0.04
0.31
0.07
0.09
0.80
0.03
0.20
0.76
0.40
69
5
33
120
130
16
65
210
16
3
51
2O
330
2O
0.11
1.95
0.06
0
4.30
0.13
2.67
4.70
0.37
0.85
12.51
1.34
7.46
63.43
70
94.89
0.02
0.26
0.25
1.97
0.01
0
0.28
0
0.07
0.01
0.38
0.45
0.42
0
3
16
0
12
1
10
1
3
13
3
110
1
Co
Ni
Zn
Rb
Sr
Y
Zr
Nb
Mo
Pb
Th
Ba
Ga
71
SiO 2
TiO 2
AI203
FeO
Fe203
MnO
MgO
CaO
Na20
K20
P205
H20 ( - )
H20 ( + )
Residuals
Sample no.
7
6
19
7
23
8
28
1
1
12
7
90.46
0.09
1.14
0.19
3.06
1.72
0.06
0.10
0.13
0.40
0.03
0.52
1.03
0.77
1300
0
72
590
0
3
5
17
6
26
4
22
3
3
16
0
92.44
0.08
1.02
0.16
1.75
1.57
0.22
0.07
0.13
0.43
0.02
0.57
1.09
0.07
73
2
11
34
13
21
7
28
3
3
20
1
86.24
0.10
1.46
0.16
4.34
3.85
0.31
0.07
0.07
0.62
0.07
0.79
1.47
0.04
2900
2
74
5
13
30
11
23
8
27
4
4
16
9
83.88
0.09
1.34
0.20
3.24
5.12
0.25
0.11
0.01
0.55
0.04
0.60
1.16
1.82
4300
2
75
90.67
0.11
1.70
0.09
3.15
1.95
0.43
0.07
0.12
0.68
0.03
0.50
1.08
0.04
1100
2
3
9
29
13
20
7
30
2
1
18
0
76
390
1
3
8
22
10
15
7
30
4
1
19
5
88.74
0.10
1.18
0.12
4.34
2.04
0.38
0.09
0
0.54
0.04
0.48
1.32
0.55
77
57.89
0.63
9.67
0.14
12.46
5.06
2.14
0.08
0.01
3.94
0.06
2.64
4.46
0.48
2000
13
15
49
120
96
33
43
130
11
2
62
18
78
11
21
55
33
32
20
63
6
3
27
7
81.62
0.25
4.05
0.19
6.01
3.47
0.94
0.08
0.20
1.44
0.02
1.02
2.27
0.23
1700
7
79
64.67
0.52
7.98
0.13
10.98
3.64
2.03
0.08
0
3.32
0.04
2.13
4.16
0.07
1100
11
13
40
100
76
23
37
110
l0
3
35
14
80
510
2
5
15
43
24
17
15
46
5
1
11
7
0.13
4.77
1.72
0.61
0.09
0.12
1.12
0.01
0.81
1.77
0.34
0.20
2.78
85.33
81
Co
Ni
Zn
Rb
Sr
Y
Zr
Nb
Mo
Pb
Th
Ba
Ga
11
40
93
74
33
38
100
10
6
52
11
2400
10
2.23
4.02
0.18
Na20
K20
0.05
0.15
3.12
Fe203
MnO
MgO
CaO
P2O5
10.81
5.1!
2.25
0.09
A1203
FeO
H20( - )
H 20( + )
Residuals
7.02
0.17
TiO2
82
(continued)
63.78
0.46
Si02
Sample no.
APPENDIX 1
8
0
57
11
1700
10
3
3
29
8
1500
2
0.18
9.77
2.73
2.10
0.08
0
2.56
0.06
1.77
3.45
0.12
0.33
3.65
2.49
1.19
0.08
0.12
0.74
0.03
0.49
1.45
0.54
12
40
99
70
27
33
120
69.96
0.43
6.24
86.25
0.15
2.18
84
6
15
37
16
28
11
49
83
4
4
12
4
590
1
4
13
21
10
29
10
50
0.17
3.05
1.27
0.28
0.10
0.11
0.56
0.03
0.58
0.95
0.47
89.51
0.10
1.50
85
3
2
17
3
260
0
2
4
16
10
19
4
41
0.17
1.26
0.08
0.27
0.06
0.06
0.55
0.02
0.45
0.56
0.61
93.44
0.09
1.71
86
4
2
10
1
240
2
3
5
16
12
16
5
29
0.16
2.53
0119
0.34
0.06
0.0
0.62
0.02
0.45
0.91
0.31
91.34
0.11
1.60
87
6
0
9
3
380
5
3
8
24
31
28
12
45
0.22
2.83
0.09
0.66
0.07
0.14
1.30
0.03
0,71
1,24
0.36
88.50
0.19
2.96
88
6
1
17
9
600
4
11
13
34
35
17
14
56
0.13
4.55
0,49
0.74
0.06
0.34
1.38
0.06
0.66
1.32
0.78
84.98
0.24
3.50
89
4
0
21
4
260
5
3
8
20
32
17
10
47
0.19
3.23
0.10
0.65
0.07
0.32
1.28
0.03
0.67
1.31
0.24
87.30
0.19
2.96
90
5
2
22
9
810
5
7
24
75
11
38
8
35
0.46
1.64
0.04
0.72
0.14
0.32
0.42
0.02
0.52
1.03
1.02
91.96
0.15
2.59
91
6
2
26
5
750
6
4
28
46
20
33
8
44
0.48
2.20
0.03
0.78
0.15
0.43
0.64
0.02
0.83
1.19
1.00
88.87
0.20
3.44
92
5
21
35
10
31
5
34
7
2
2O
4
1100
4
9
59
98
120
40
32
130
10
3
30
9
990
17
Ga
3.65
3.86
0.61
Co
Ni
Zn
Rb
Sr
Y
Zr
Nb
Mo
Pb
Th
Ba
I-I20(+ )
Residuals
H zO( - )
P2O5
Na20
K20
Fe203
MnO
MgO
CaO
0.02
0.65
0.12
0.55
0.37
0.02
0.73
1.02
0.74
0.15
2.58
0.43
1.47
0.75
12.00
0.91
6.32
0.03
2.27
0.27
0.20
3.89
0.04
T10 2
A1203
FeO
90.84
94
63.95
93
SiO 2
Sample no.
3.54
0.05
3.73
4.73
0.14
0.36
0.40
0.80
13.05
0.75
6.22
0.04
2.06
63.57
21
9
70
130
120
54
39
150
14
1
74
14
3400
95
3
7
18
26
8
38
6
31
3
3
11
2
970
0.35
0.37
0.04
0.44
1.05
0.58
96
92.38
0.13
1.79
0.46
0.99
0.01
0.39
0.11
3.86
4.07
0.28
0.78
12.11
0.70
5.72
0.04
2.08
0.35
0.38
3.33
0.04
65.09
7
57
98
110
39
33
130
11
2
32
17
1600
18
97
0
0.83
0.12
0.32
0.64
0.02
0.54
1.22
0.83
0.18
2.70
0.44
1.44
90,70
3
0
1600
3
18
31
19
31
8
41
5
1
16
98
3.57
0.06
3.14
4.53
0.09
5.99
0.04
2.20
0.24
0.27
65.45
0,77
12.90
0.44
19
110
39
35
140
12
2
47
16
1200
8
59
100
99
3
8
1100
28
12
27
4
32
6
1
7
2
12
0.50
0.05
0.40
0,84
0.58
0
0.41
0.01
0.13
92.91
0.15
2.11
0.49
1.02
100
23
57
12
1900
130
42
41
150
14
1
12
64
140
0.07
4.34
5.81
0.30
101
58.48
0.93
14.48
1.20
6.70
0.05
2.56
0.35
0.21
4.23
1
89O
1
5
2
47
4
18
37
16
34
8
34
1.33
0.34
0.51
0.03
0.51
0.I0
0.52
102
92.53
0.14
2.17
0.31
1.21
0.01
0.54
22
59
18
1700
73
140
150
49
46
170
17
2
12
4.50
6.34
0.24
2.85
0.38
0.26
4.69
0.07
1,09
7.78
0.06
15.48
0.98
103
54.35
,...a
1.83
0.01
0.59
0.13
0.51
0.59
0.03
0.52
1.01
1.12
5
19
35
16
33
9
36
6
2
11
5
1800
2
Fe203
MgO
CaO
Na20
K20
P205
H20( - )
H20( + )
Residuals
Co
Ni
Zn
Rb
Sr
Y
Zr
Nb
Mo
Pb
Th
Ba
Ga
MnO
89.14
0.18
2.70
0.38
104
(continued)
SiO 2
TiO2
A1203
FeO
i
Sample no.
APPENDIX 1
1100
0
22
11
53
5
30
4
3
50
1
3
9
0.45
0.01
0.29
1.03
1.41
0.56
0.10
0.73
1.21
0.02
91.16
0.14
2.02
0.36
105
0
5
27
5
2
21
0
990
3
10
22
11
46
0.41
0.33
0.84
0.10
0.48
0.47
0.03
92.11
0.12
2.05
0.41
1.13
0.01
0.49
106
31
11
27
6
27
4
1
62
0
850
0
3
9
1
6
18
3
22
4
21
3
1
48
2
510
1
0.01
0.27
0.67
0.44
0.09
2.14
0.26
1.08
0.03
0.30
0.08
1.13
0.24
0.13
2.13
0.61
1.21
0.03
0.60
0.09
0~46
0.45
0.03
0.38
1.03
0.61
92.31
108
92.92
107
17
0
190
15
1200
28
3
600
1
11
61
200
160
51
62
190
0.12
3.87
5.43
0.04
54.74
1.02
17.13
1.01
7.05
0.10
2.86
0.32
0.47
4.87
110
3
10
29
9
35
7
26
4
2
49
0.89
0.03
0.41
0.09
0.19
0.40
0.03
0.28
0.65
0.77
0.12
1.91
0.44
94.81
109
0
55
0
75O
3
4
15
36
12
35
I0
3O
5
0.71
1.27
0.29
0.68
0.11
0,06
0.43
0.05
2.28
0.04
89.95
0.14
1.95
0.43
111
57
59
160
18
1
340
11
2200
26
12
56
170
140
0.11
2.52
0.32
0.53
4.19
0.14
3.46
4.80
0.43
57.87
0.91
15.80
1.01
6.64
112
8
610
2
4
11
26
14
39
10
30
3
3
37
0.45
1,08
0.34
92.15
0.13
2.01
0.34
1.62
0.02
0.50
0.10
0.33
0.49
0.04
113
6
7
20
33
14
39
7
29
3
3
56
6
790
0.50
1A2
0.34
91.71
0.14
2.51
0.40
1.41
0.02
0.62
0.09
0,14
0.53
0.04
114
4
14
37
14
32
8
30
3
3
11
4
490
3
Co
Ni
Zn
Rb
Sr
Y
Zr
Nb
Mo
Pb
Th
Ba
Ga
1
49
7
680
4
30
12
49
6
30
3
3
11
91.34
0.14
2.60
0.53
0.97
0.02
0.69
0.11
0.13
0.53
0.02
0.38
1.12
0.42
116
6
310
6
890
25
160
150
45
50
170
11
14
41
61.66
0.88
14.83
0.99
6.87
0.08
2.51
0.25
0.68
4.60
0.06
2.45
4.74
0.20
117
3
49
5
840
4
42
16
50
9
36
3
9
14
91.73
0.16
3.03
0.39
2.36
0.09
0.68
0.11
0.16
0.56
0.05
0.45
1.34
0.13
118
3
240
13
890
23
140
140
45
47
150
13
7
35
61.19
0.86
14.51
1.10
6.87
0.06
2.33
0.23
0.34
4.66
0.06
2.32
4.65
0.18
119
4
49
0
780
3
25
10
46
5
27
4
3
9
94.11
0.12
2.17
0.34
1.15
0.04
0.37
0.10
0.19
0.44
0.02
0.31
1.01
0.16
120
5
39
4
480
4
24
15
29
8
29
4
2
6
93.50
0.12
2.25
0.35
1.00
0.03
0.49
0.09
0.21
0.52
0.01
0.37
0.77
1.64
121
3
29
4
200
1
24
7
16
2
14
4
0
3
97.08
0.06
1.14
0.19
0.35
0.01
0.18
0.06
0.11
0.29
0.02
0.29
0.60
0.17
122
0
31
5
350
3
34
19
26
8
26
5
1
3
93.24
0.10
2.27
0.23
0.61
0.03
0.35
0.12
0.18
0.59
0.05
0.34
0.83
0.71
123
2
47
5
330
4
62
20
23
10
28
3
3
8
91.65
0.12
3.02
0.45
1.18
0.09
0.68
0.10
0.06
0.70
0.09
0.68
1.29
0.73
124
3
47
1
410
7
46
29
34
20
39
5
3
7
90.46
0.14
3.47
0.41
0.84
0.08
0.50
0.19
0.16
0.87
0.16
0.61
1.35
0.31
125
5
33
5
320
3
29
14
28
6
27
2
1
4
94.74
0.10
2.02
0.25
0.58
0.05
0.34
0.10
0.13
0.47
0.05
0.32
0.76
0.40
126
Residual materials are calculated by subtracting H 2 0 from ignition loss. They may contain sulfur, organic materials and others. Compounds in %; elements
in ppm.
91.88
0.13
2.54
0.41
1.26
0.04
0.64
0.10
0.20
0.53
0.04
0.39
1.03
0~44
115
SiO 2
TiO 2
A1203
FeO
Fe203
MnO
MgO
CaO
Na20
KzO
P2Os
HzO ( - )
H20 ( + )
Residuals
Sample no.
41
110
5
0
0
1
150
21
Y
Zr
Nb
Mo
Pb
Th
Ba
Ga
11.49
4.59
8.58
0.17
5.74
5.52
2.07
0.82
0.19
5.77
0.67
2.60
0.15
AI203
FeO
Fe203
MnO
MgO
CaO
Na,20
K20
P205
CaCO 3
H20( - )
H20( + )
Residuals
29
57
150
11
130
48.28
2.00
SiO2
TiO 2
Co
Ni
Zn
Rb
Sr
1
Sample no,
110
17
30
68
5
7
0
0
26
54
130
8
140
13.34
3,68
7.53
0.14
5.35
9.81
2.59
0.80
0.15
5.04
0,41
1.56
1.72
48.51
1.35
2
110
18
34
89
2
12
0
0
27
55
120
0
91
12.23
3.21
10.74
0.18
4.76
11.89
2.72
0.02
0.15
3,33
0.38
2.53
1.03
45.48
1.55
3
Analyses of samples from the Shimanto Terrane
APPENDIX 2
13.91
5.92
5.28
0,20
6,69
6.03
3.23
0.47
0.41
3.03
0.97
3.49
1.62
48.41
2,03
220
16
35
140
19
1
2
0
20
66
95
3
210
4
13.31
4.34
7,51
0,20
6.57
7.25
3.27
L12
0,18
1.18
0.90
2.53
0.09
50.37
1.80
140
13
42
88
6
5
0
0
27
54
130
17
220
5
1,59
0.97
2.97
0.97
0.83
2.38
0.15
0.14
0.08
5.45
0.39
1. i 1
1.66
79.29
0.06
80
4
19
8
0
7
9
0
5
37
100
4
35
6
0
1.66
4.45
0.56
0.13
1.14
0~85
4.89
3.10
0.42
2:65
0.65
16.72
2.27
59.38
3
19
3O
300
22
37
29
180
18
14
59
140
180
7
180
8
3
12
2O
33O
24
7
52
110
13
45
16
17
1
16
8
3
22O
3
3.22
0:25
0.71
2.54
0.05
1.25
1.58
2.89
1.74
1.47
0.21
0.29
0.29
0.06
85.32
15
3.97
1.26
3.98
0.35
2.63
1.41
0.97
5.11
0.11
0
1.22
17.08
1.37
60.03
0.62
9
57
150
180
49
21
8
5
130
7
51
0
2O
44
67
9
62
110
44
140
1.16
8:92
8,23
0.40
1.26
0.28
2.30
0.47
1.62
1.99
4.24
1,64
9.27
59.50
0.23
10
9
4
14
26
340
19
48
130
170
200
27
140
13
1.18
0.93
4.79
0,13
0
1.34
3.84
3.58
2.49
16.53
3.55
2.01
0.44
60.03
0.63
11
13
49
130
180
180
24
150
11
8
7
20
54
21
1,51
1.09
4.84
0.11
0
1.34
3.62
4,19
1.57
0,39
2.64
59.31
0.62
16.62
3:92
12
280
17
Ba
Ga
140
6
0
23
3
71
160
17
140
41
22
3
210
1
9
18
14
47
140
14
99
23
9
2
8
0.10
0.34
0.32
0.11
4.48
0,35
0.56
1.03
83.17
0.06
1.10
0.60
5.33
1.56
1,39
15
260
2
1
16
2
42
130
12
73
14
8
3
9
0.97
0.23
0.26
0.08
2.71
0.61
1.05
1.57
85.31
0.07
1.55
0.51
3,52
2.20
1.30
16
890
2
5
11
0
31
97
6
88
10
0
1
2
2.16
0.37
0.14
0.08
4.56
0.31
0.74
1.39
85.66
0.04
0.51
0.13
2.04
0,96
0.54
17
190
2
4
0
0
16
60
14
40
8
6
1
2
0.28
0,26
0,29
0.05
0
0.22
0.61
0.45
96.03
0.04
0.96
0,11
0.98
0.15
0.20
18
170
5
6
7
0
49
110
8
110
12
6
3
3
3.90
0.06
0.20
0.09
9.48
0.44
0.75
2.74
75.95
0.05
1.21
0,22
2,46
1.02
0.52
19
120
0
17
7
3
35
49
6
71
7
5
0
3
3.36
0.28
0.17
0.004
9.42
0.26
0,77
0.32
82.45
0.04
0.49
0.25
2.11
0.92
0.50
20
89
3
14
2
3
16
55
7
53
8
0
0
1
1.81
0.39
0,18
0.61
3.08
0.15
0.41
0.54
91.44
0.03
0.58
0.26
1.03
0,52
0.26
21
110
4
0
19
0
58
150
6
350
38
0
4
8
3,11
0,44
0.20
0.27
33,26
0,77
1.23
0.09
47.65
0.08
1.44
0.37
6.88
2.68
1.97
22
160
7
4
0
7
25
69
19
19
5
9
0
4
0,13
0.45
0,41
0.04
0
0.34
0.63
0.56
93.41
0.07
1.85
1.01
0.80
0.11
0.48
23
120
4
10
9
1
51
130
1
40
17
9
3
8
0.47
0,53
0.08
0.09
1,20
0.69
1.38
0.28
88.07
0.05
1.55
0.21
3,99
1.53
1.57
24
Residuals are calculated by subtracting H 2 0 from ignition loss. They may contain sulfur, organic materials, and others. Compounds in %; elements in ppm.
4
8
24
Mo
Pb
Th
10
7
22
120
130
130
14
150
9
Co
Ni
Zn
Rb
Sr
Y
Zr
Nb
1.32
0.18
0.41
0.22
6.02
0.48
1.10
1.68
0.05
1.35
3.90
0.11
5.58
0.81
3.06
0,58
CaO
Na20
K20
P205
CaCO 3
H20 ( - )
H20 (+)
Residuals
72.71
0.10
2.35
1.01
7.72
1.88
1.31
63.53
0.58
16.35
3.02
0.94
0,15
1.48
SiO 2
TiO 2
A1203
FeO
Fe203
MnO
MgO
14
13
Sample no.
106
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