Junction: Paleocene Hidaka Belt, central Hokkaido, Japan. Palaeogeogr., Palaeoclimatol. ..... are characterized by low to high AI and low Fe 3 + compositions.
Pahwogeography, Pahwoclimatology, Pa&eoecoh~gy, 105
(1993): 53 69
53
Elsevier Science Publishers B.V., A m s t e r d a m
Sedimentary petrology and paleotectonic analysis of the arc-arc junction: the Paleocene Nakanogawa Group in the Hidaka Belt, central Hokkaido, Japan Futoshi N a n a y a m a a, Toshiya K a n a m a t s u b and Yoshiki Fujiwara ~ Department ~)fGeology and Mineralogy, FaculO' ()f Science, Hokkaido University, N-IO, if-8. Kita-ku, Sapporo 060, Japan b Ocean Research Institute, University ~?/ Tokyo, 1-15-1 Minamidai, Nakano-ku, Tokyo 164. Japan
(Received December 16, 1991~revised and accepted April 30. 1993)
ABSTRACT N a n a y a m a , F , K a n a m a t s u . T. and Fujiwara, Y., 1993. Sedimentary petrology and paleotectonic analysis of the arc-arc Junction: Paleocene Hidaka Belt, central Hokkaido, Japan. Palaeogeogr., Palaeoclimatol., Palaeoecol., 105:53 69. Two arc trench systems have been recognized by using paleomagnetic data in the Hokkaido Central Belt, northeast Japan, during Late Cretaceous to Early Paleogene: the Paleo-Japan and the Paleo-Kuril arc-trench systems. The Hidaka Belt is composed mainly of Paleocene turbidite facies, with a small a m o u n t of hemipelagic sediment and melange facies. These sediments accumulated near the trench area, later composed accretionary bodies in the two arc trench systems. The N a k a n o g a w a G r o u p is typically exposed on the southern side of the Hidaka Belt. This group is divided into three petroprovinces; zones I-III, from south to north on the basis of sedimentary, petrological and paleocurrent analyses. The modal component of sandstones from zone I indicate that they are characteristically rich in volcanic rock fragments (intermediate to basic composition), clinopyroxene, hornblende and poor in quartz. The characteristics of zone I are similar to those of forearc to slope basin sediments in the Paleo-Kuril arc-trench system. The modal component of sandstones from zone Ill consists predominantly of monocrystalline quartz, K-feldspar, acidic volcanic fragments, radiolarian chert and tectonite fragments, similar to those of forearc basin sediments of the Paleo-Japan arc trench system. The modal component of rocks from zone II are regarded as being intermediate between zones I and Ill. However, clinopyroxene and chromian spinel chemical data suggest that the sandstones of zones I and II were derived from the Paleo-Kuril arc region. The sediments of the Hidaka Belt were thus derived from two different arc trench systems and deposited in the arc arc junction area during the Paleocene.
Introduction
Since the early 1970s, the geology of the Hokkaido Central Belt, has been regarded as the product of accretion and collision systems (e.g., Horikoshi, 1972; Dickinson, 1979; Okada, 1979, 1983; Kimura, 1985; Kimura and Tamaki, 1985a, b). In central Hokkaido, two palaeo-arc trench systems are recognized by using geophysical and paleomagnetic data (Segawa and Oshima, 1975; Segawa and Furuta, 1978; Kimura and Tamaki, 1985a, b; Kimura, 1990; Kanamatsu and Nanayama, 1992: Kanamatsu et al., 1992; Figs. 3 and 4), one which underwent westward subduction beneath the northeastern margin of Eurasia (Paleo0031-0182/93/$06.00
:t"~ 1993
Japan arc trench system: PJS), and the other which underwent a northward subduction beneath the southern margin of the Okhotsk continental block (Paleo-Kuril arc-trench system: PKS) during the Late Cretaceous to the Late Eocene (90 35 Ma). The Hokkaido Central Belt consists of several tectonic units, the Sorachi-Yezo Belt, the Idonnappu Belt, the Hidaka Belt, the Tokoro Belt and the Nemuro Belt from west to east (Figs. la, b and 2: references from Okada, 1979, 1983: Kimura, 1985: Kiminami et al., 1986; Niida and Kito, 1986: Nanayama, 1992a, b: Kiyokawa, 1992 and Figs. 3 and 4). The Sorachi-Yezo Belt is composed of forearc to slope basin sediments (Yezo Supergroup; Okada, 1983) during the Late
Elsevier Science Publishers B.V. All rights reserved.
54
F. NANAYAMA ET AL.
Sorachi-Yezo Belt 130"
::::::::::::::::::::::::
~,~~
SEA OF JAPAN
Fig.1 b)
s~o
y/~
PHILIPPINE SEA PLATE
(b)
Fig. 1 (a) Simplified tectonic map around Japan, eastern Eurasia. (b) Tectonic divisions within central Hokkaido (modified after Kiminami et al., 1986; Niida and Kito, 1986). A = Hakobuchi Group in the Sorachi area; B = Hakobuchi Group (Utsunaigawa Formation) in the Nakatonbetsu area; C = Menashuman Formation in the Hidaka-horobetsu River; D = Nakanogawa Group; E = Saroma Group; F = Nemuro Group in the Shiranuka area. For location see (a).
'
~
30-
~
~
~
!Sorachi-Yezo Belt
Eocene
Hidaka Belt (Nakanogawa Gr.) zone I zone' III zone II
'"
Pale. . . . .
Maas~.
Idonnappu Belt ON SB. Koiboku SB.
E
.~
BarT. Hau~
~5o200-
...... ,.........
250300 -
1
[]
Berdas. Valan~.-' - ~[ ~'~"
0
I ~ .~',
#.
Triassic
0 gg@g g
Por. ..
0
Carboniferous
ii!ii!!i
t3
;
Jurassic
[~="k54.0K
I
"j
%:!!i::i!
lOO-
UrahoroGr.
__BE__ _ _ l l _ _ _ _ l l _ _ ~
_ _ Santon. - - - Coniac. - -
Nemuro Belt
~,~r.38,
"58.5K
~
~67,4F i:~I •/r75.6F ::~
Tokoro Belt
g
ILegend I
~
Foreare basin and slope basin sediments Accretsd oceanic crast ($orachi Group)
I
Turbidite
B
Hemipelagite
Accreted sediments
Bedded red chert Limestone
Fig. 2. Generalized columns for the central Hokkaido. Data are mostly based on the following papers: Okada et al., 1984; Kaiho, 1984; Watanabe and Iwata, 1985; Kito, 1987; Okada et al., 1987; Watanabe and Iwata, 1987; Kimura, K. and Tsuji, 1988; Kiyokawa, 1989, 1992; Kiminami et al., 1990; Kaiho et al., 1990; Akiyama et al., 1990; Nanayama, 1992a; Ueda et al., 1992; Kurita et al., 1992; Yasuda, 1986. F = fission track dating; K = K - A r dating.
SEI)IMENqARY PETROLOGY AND PALEOTECTONIC ANALYSIS OF ARC ARC JUNCTION: PALEOCENE HIDAKA BELq, HOKKAII)O
Nemuro & Urahoro Groups (late Cretaceous -late Eocene)
55
,~.~.
+
".. Nakanogawa Group (early Paleoeene)
- J \
\
/
J
/ /
f
J
acoustic basement
° // / /'
ItT2W~ r:~n2al
/
Nemuro Group (late Cretaceous- early" Paleogene)
Saroma Group (late Cretaceous) Fig. 3. Paleomagnetic directions of the eastern Hokkaido area. Arrows showing paleomagnetic directions after K a n a m a t s u et al. (1992), K a n a m a t s u and N a n a y a m a (1992), Tanaka and Uchimura (1989) and H a m a n o et al. (1986).
Valanginian to Paleocene, and stratigraphically above accreted oceanic crust or plateau (Sorachi Group and Hidaka Western Greenstone Belt) of the PJS. This belt includes high-pressure metamorphic rocks of the Kamuikotan Zone and consists of a serpentine melange facies. The Idonnappu Belt is an accretionary complex of the PJS formed during the Early to Latest Cretaceous (Hauterivian to Maastrichtian; Kiyokawa, 1989, 1992; Ueda et al., 1992), with slope basin sediments : Menasyuman Formation (Late Campanian to Paleocene; Sakai and Kanie, 1986; Kiyokawa, 1989, 1992; Ueda et al., 1992). The Idonnappu Belt ranges in age from Early to Latest Cretaceous with a clear progression from older ages in the west to younger ages in the east. The Tokoro Belt consists of tile Nikoro and Saroma Groups, of
which the former is an accreted seamount complex of the southern margin of the Okhotsk continental block, and formed an accretionary prism of the PKS during Late Cretaceous time (Research Group of the Tokoro Belt, 1984; Kiminami et al., 1986; Sakakibara, 1986; Sakakibara et al., 1986). The Saroma Group is characterized by slope basin sediments of the PKS, and unconformably overlies the Nikoro Group during the Middle Campanian to Paleocene (Sakakibara et al., 1986; Okamura and Kimura, 1989; Akiyama et al,, 1990). The Nemuro Belt consists of forearc basin sediments of the PKS, formed along the southern margin of the Okhotsk continental block (Kiminami, 1983) during Middle Campanian to Middle Eocene (Kaiho, 1984: Okada et al., 1987). However, the tectonic setting of the Hidaka Belt has not become
~6
F. NANAYAMA ET AL.
::::::::::::::::::::::::::::::::::::::::::::::::::::::: Arc (Okhotsk Block)]:::::
::::::,[Paleo-Kuril !i:::~i~:~::
.~~
INemuro Belt
~;
....
" --
nch ]
:a. 35 Ma (Late EoceneJ
~..':..~~o_::::::::l'Pa[eoLK,~rilArc (OkhotskBlock)J IHidakaBelt~It~:i~ ~ "'::::.:.:.:.:.:.:.:.:.
\
~m~lilclA~lClltl~ll.~lA~lr.z~nr~riI~z¢~,~la~ ~
N
"" , I / , ~ N~muro Belt (Shiranuka Area) l "~ o
ii
: D ~,~
\
migration of the Kuril
o"
,,O
\ , y ~ ~
(Konsen Coast Area}~
\
[Hidaka Belt (Na_kanogaw~rou~ Fig. 4. Tectonic reconstruction of the eastern Hokkaido area during the Late Cretaceous to Quaternary. Modified after Kanamatsu et al. (1992) and Kimura and Tamaki (1985a, b).
clear. Kiminami et al. (1986) and Komatsu (1985) proposed that the Hidaka Belt represents the collision between two subduction systems. Alternatively, Kimura (1985) suggested that the Hidaka Belt represents a Late Cretaceous accretional complex associated with subduction of an oceanic plate beneath the Eurasia. Previously, the following problems had not been resolved in relation to the Hidaka Belt.
(1) Were the sediments of the Hidaka Belt related to the tectonic setting of the PKS or the PJS.9 (2) Were the sediments of the Hidaka Belt derived from the PKS or the PJS? Therefore, we have attempted to answer those questions using a sedimentary petrological approach in the Nakanogawa Group, Hidaka Belt. The results and conclusions are presented below.
S[ I)IMEN FARY P E ' I R O L O G Y A N D P A L E O T E C I O N I C ANALYSIS OF ARC ARC J U N ( ' T I O N : PALEOCENE H I D A K A BELI, H O K K A I D O
Geological setting of the Nakanogawa Group, Hidaka Belt Figure 5 is a geological map of the southern central Hokkaido. The Nakanogawa Group is distributed along the eastern side of the Hidaka mountain range (Kontani, 1978), and is included in the Hidaka Belt (Nanayama, 1992a, b). The Nakanogawa Group is composed mainly of Paleocene turbidite facies. It also contains a small amount of hemipelagic sediment and melange facies including exotic blocks of greenstone, red chert and micritic limestone deposited during Barremian to Turonian (Fig. 2). The same sequence of turbidite facies are often repeated as a result of faulting and folding. Such turbidite facies must have accumulated near the trench area, and contributed to the respective accretionary bodies later (Nanayama and Kiminami, 1989; Nanayama, 1992a, b).
57
The Nakanogawa Group is divided into two tectonic units, bounded by the Nupinaigawa fault system (Fig. 5; NF). This fault is considered to be a right-lateral strike-slip fault system (Nanayama, 1992a). Four typical sections, from the Hiroo coast area, the Toyonigawa area, the Rekifunegawa area and the Biseigawa area, from south to north, are petrologically discussed in detail below (Fig. 5).
Sedimentary petrology of the Nakanogawa Group, Hidaka Belt
Three petroprovinces of the Nakanogawa Group Compositional analyses of sandstones were determined according to the methods established by Dickinson et al. (1983) and Kiminami et al. (1983), in order to understand the petrographical significance of the Nakanogawa Group (Nanayama, 1992b) though some modifications
140E
144 E
44w 2 - _ _
~-
42"N
Hidaka Belt (N akanogawa Group)
line
Turbidite Facies
UniJ
llornfels Zone Melange Facies
',\
~
Yezo Supergroup H.W.G.B. Idonnappu Belt
~
Tokoro Belt
~
H.M.B.
1
H.M.W.B. Peridotite
"1 ~ HI=
o
20
,o:k~T~
I ldonnappu Belt I
Fig. 5, Geological map of the southern central Hokkaido showing the distribution of the Hidaka Belt (Nakanogawa Group). N F = Nupinaigawa fault: H F = Hiroo fault; H . C . A . - Hiroo coast area; T .R.A.= Toyonigawa area: R . R . A . = Rekifunegawa area: B.R.A. = Biseigawa area. H. W.G,B. = Hidaka western greenslone belt: H.M.B. = Hidaka metamorphic belt: H . M . W . B . - Poroshiri Ophiolite; PO = Mt. Poroshiri; P E = Mt. Petegari; K= Mt. Kamui; R - Mt. Rakko; T= Mt. Toyoni.
58
F. NANAYAMAET AL.
such as counting more than 500 points in one thinsection for each specimen (grid spacing 0.5 x 0.5 mm), and the inclusion of grains smaller than 0.02 mm into the matrix were made. We have dealt with only medium-grained sandstones. Volcanic rock fragments are further subdivided into 4 types according to groundmass textures. Volcanic 1 type (V.1) is composed of aphanitic, aphyric, felsic perlitic, spherulitic, eutaxitic and variolitic textures, derived from acidic volcanics. Volcanic 2 type (V.2) displays pilotaxitic, hyalo-ophitic and hyalopilitic textures, and have been derived from intermediate volcanics. Volcanic 3 type (V.3) displays intergranular and intersertal textures, derived from basic volcanics. Volcanic 4 type (V.4) displays a trachytic texture. The combination of sandstone petrology, paleocurrent and paleoslope data reveal the existence of three petroprovinces : zones I, II and III in the Nakanogawa Group (Nanayama, 1992b; Table 1 and Figs. 6 and 7) based on the concept of petroprovince as proposed by Okada (1989). Zone I
Zone I is distributed along the Hiroo coast area, in the Toyonigawa area and along the eastern side
of the Rekifunegawa area (Fig. 6). The sandstones of this zone are subdivided into two types: H- and K-types (Table 1). The H-type sandstones have the following characteristics (Table 1). (1) Dominant paleocurrent and paleoslope directions from SSE to NNW (axial current), from SE to NW, and from E to W (lateral current). (2) A low Qz/(Rf+ Fd) ratio (Qz: quartz, Rf: rock-fragment, Fd: feldspar), lower than 0.1. (3) Quartz grains having a corroded form suggesting they have been derived from acidic volcanics. (4) Plagioclase grains having a normal zonal structure, glomeroporphyritic texture and strongly altered. (5) Rich in volcanic rock-fragments, more than 8.3%. (6) High contents of V.2 (17.0%) and V.3 (2.0%), but poor in V.I (10.6%). (7) Abundant pumice and scoria fragments. (8) Relatively high contents of accessory minerals (heavy minerals + mica), on average 2.5%, with a maximum of 8.3%. The main minerals include clinopyroxene, hornblende, biotite with a small amount of opaque minerals.
TABLE 1 The three petroprovinces of the Nakanogawa Group and their characteristics. Q z = quartz, F d = feldspar, R f = rock-fragment. Average (Standard). Cpx = clinopyroxene, Bt= biotite, H b = hornblende, O p x = orthopyroxene, Z r = zircon, O q = opaque minerals, G a r = garnet, Chr = chrome spinel, Tour = tourmaline, Mt = muscovite, Ap = apatite. Zone & Type
Paleocurrent
Modal composition Rate of Qz./Fd/Rf
& Paleoslope
ZONE I
H-type
SSE to NNE
Oz/(Fd+Rf)
(axial c~'rem)
EtoW
:0.1 (0.1) Fd/Rf
(lateral cam'oat)[
SSE to NNE
K-type
VoL : 30.5 (8.3
V2:17.0 (7.1) • VI: 10.6 (3.0)
• Meta. : 0.8 (1.0
:0`1 (0.1) F-d/Fff
Z O N E II
Oz/(Fd+Rf)
(axial curfeW)
:0.2 (0.1) Fd/Rf
Vol. : 29.5 (7.6
Z O N E III
Qz/(Fd+RO
(axial ~ t )
:0.4 (0`1) Fd/Rf :0.4 (0.1)
V.I: 18.9 (6.2)
>> Seal. : 5.2 (4.2]
• V.2:8.5 (3.6)
• Meta. : 1.2 (1.6
> V.3:0.9 (0.8)
Max: 8.3
V.I: 14.4 (5.3) • V.2:8.3 (4.1)
• Meta. : 2:7 (1.5)
> V.4:1.0 (0.7)
V.l: 17.9 (4.4)
> Seal. : 7.7 (3.5)
> V.2:?--9 (1.7)
• Meta. : 0.9 (0.8)
• V.3:0.6 (0.4) • V.4:0.3 (0.4)
Cpx >> Bt
Ave: 2.5 (2.0) • Zr, Oq, Gar, Chs, Mt Max: 5.6
Bt > Cpx >Oq >Zr
Provenance Area After Dickinson et at. (1983)
*Undissected Arc (to Transitional Arc) * A c t i v e arc front
*Paleo-Kuril Arc od#n *Undissocted Arc to
Transitional Arc
Ave: 1.9 (1.6) > Hb > Opx, Tour *Active arc front Chs, Gar, Mt Max: 4.7
Bt > Cpx >Zr>Oq
*Paleo-Kta-il Arc ori#n *UndLssectedArc to Transitional Arc
Ave: 2_5 (1.0) > Hb • Opx, Tour * A c t i v e arc front
• V.3:1.0 (1.0) Vol. : 21.8 (4.5)
Composition
>Hb >Opx
> VA: 0_8 (1.4) Vol. : 25.0 (5.8) i > Seal. : 13.3 (3.5)i
:0.4 (0.1) NtoS
• V3:2.0 (2.1)
Rate (%)
> V4:0.9 (0.6)
:0.4 (0.2) NE to SW
Accessary minerals
Rate of VoL Rt. (%]
>> Sed. : 6.5 (4.7]
:0.4 (0.2)
Qz/(Fd+RO
(axial o.¢m~)
Rate of Rt (%)
C~s, Gar, Mt Max: 3.6
Bt >Zr>Oq
Ave: 0.9 (0.8) • cpx, Tour, Ctts, Gac Mt
*Paleo-Kuril Arc origin *Transitional Arc Io Dissected Arc *Active continental margin? * Paleo-Japan Arc ociF~in.9
SEDIMENTARY PETROLOGY AND PALl OTECTONIC ANALYSIS OF ARC ARC JUNCTION: PALEOCENE HIDAKA BELT, H O K K A I D O
59
Pa
Pa
0
44~N ~
42"N-
I ldonnappu Belt I Fig. 6. Three petroprovinces identified in the Nakanogawa Group (Hidaka Belt) showing their paleocurrent and paleoslope directions.
Half of these grains are altered into epidote group minerals. (9) Matrix content is usually more than 15%, including lithic wackestone (Okada, 1971). Therefore, the H-type sandstones can be referred to as a volcanic lithic wacke stone, which must have been derived from (1) an immature and undissected arc region or (2) an active volcanic arc region. The modal component of K-type sandstones seems to be nearly the same as the H-type (Table l ), though a number of minor differences are apparent as follows. (1) V.I content is slightly higher than the V.2 content. (2) K-type rocks contain slightly angular monocrystalline quartz. (3) Accessory mineral contents are lower than 1.9%, and rich in biotite and zircon (euhedral). Zone H
Zone II is distributed in the main part of the Rekifunegawa area (Fig. 6). The sandstones of this zone have the following characteristics (Table 1).
(1) A variation in paleocurrent directions from NE to SW. (2) A Qz/(Fd + Rf) ratio (0.2) is slightly higher than that of the K-type. (3) V.1 content (14.4%) is slightly higher than the K type. (4) Average abundance of accessory minerals is 2.2%, with a maximum content of 4.7%, which is almost the same as the K type.
Zone I I I
Zone III is distributed in the Biseigawa area. The sandstones of this zone have the following characteristics (Table 1). (1) Dominant paleocurrent directions are from NtoS. (2) A high Qz/(Rf + Fd) ratio, average 0.4. (3) Contains abundant polycrystalline quartz. (4) High V.I content (17.9%). (5) Low contents of accessory minerals (less than 2%), which includes biotite, zircon (euhedral type) and tourmaline.
60
F. NANAYAMAET AL. Qm
PI
J
.
I ' ~ I d['~ [ ~ l l
.
.
Qm
.
Qm
.
Qm
.
Qm
+'~
Qm
Qm
Qm
- -
, . ~ i k
V.1
V.1
V.I
VI
V.2
V.I
V.I
V.I
V.I
l l h , ~
.'Z 2
V.3
Fig. 7. Ternary Qm-P1-Kf, V.1-V.2-V.3 diagrams of sandstone compositions from the central Hokkaido (Hakobuchi Group: Sorachi-Yezo Belt; Menasyuman Formation: Idonnappu Belt; Nakanogawa Group: Hidaka Belt; Saroma Group and Nemuro Group) during Latest Cretaceous to Paleocene. Qm = monocrystalline quartz, PI = plagioclase, Kf= K-feldspar.
(6) Includes many chert, quartz schist and mica schist fragments. (7) These sandstones were derived mainly from acidic volcanics, sedimentary and plutonic rocks distributed in an orogenic zone of an arc.
Bulk chemistry Bulk chemical analysis (Major element) of sandstones from the central Hokkaido (Nakanogawa, Nemuro, Saroma and Hakobuchi Groups) were measured for 42 samples using the fluorescence X-ray analyzer (Phillips PW 1404) at Hokkaido University following the analytical procedures of Tsuchiya et al. (1989). Selected results are presented in Table 2. Considering the following effects; (1) alteration by sea water affecting K20 and Na20 concentrations, (2) albitization of plagioclase grains (e.g.,
Kumon, 1992), and (3) diagenesis, we have two diagrams following the discussion of Bahatia (1983) (Fig. 8). The bulk chemical data of sandstones from zones I and II (Nakanogawa Group, Hidaka Belt) are plotted near the fields of these from the Nemuro and Saroma Groups (Nemuro and Tokoro Belts), and almost included in the fields of the Oceanic Island Arc and Continental Island Arc (Bahatia, 1983). They have high contents of FeO* + MgO (wt%), A1/O3/SiO2 and TiO2 (wt%). The data from zone III are not concentrated, but are almost plotted near those of the Hakobuchi Group (uppermost part of the Yezo Supergroup in the Sorachi-Yezo Belt ; Fig. 2), and included in the fields of the Oceanic Island Arc, Continental Island Arc and Active Continental Margin (Bahatia, 1983). However, the A12Oa/SiOz ratio of sandstones from zone III and the Hakobuchi
SEDIMENTARY PEI ROLO(;~ AND PALEOTECTONIC ANALYSISOF ARC" ~RC JUNCI ION: PALEOCENE HIDAKA BELl-, HOKKAII)O
61
]-ABLE 2 W h o l e rock c o m p o s i t i o n s o f the s a n d s t o n e s f r o m the N a k a n o g a ~ a (zones I, I1 a n d I l l ) , N e m u r o a n d H a k o b u c h i Ciroups in the central H o k k a i d o . FeO* = T o t a l FeO.
No. SiO2 TiO2 AI203 FeO* MrO
MgO CaO Na20 K20 P205 iolal(wl%} Cr(ppm) Ni(ppm)
Nak.mloqawa Grou~ ZONE I hr 01 hr-02 61 57 057 15.07 4.22 t" 28 1.56 10.61 3.56 2.95 0.17 100.56 12 14
hr-03
ZONE II ~m 01
hr04
No. SiO2 TiO2 IAI203 FeO" IVlnO CaO Na20 K20 P205 Tolal(wt%) Cr(ppm) Ni(ppm)
~,rn 04
59 i~
66 09
68.20
67,90
67 99
0.74
0.81
0.7c
16.92 7.06
16.96 8 17
15.61 5.84-
0 85 16.28
069 15.17
0.59 15 93
0 70! 1489
0 13 2.66 4.08 2.72
0.08 2.96 1.65 2.90
0 25 214! 11.65 3 11
7.05 005 3.38 1.04
5 71 066 I 94 1 20
4 77 066 1 78 2 04
5 73 066 309 1.82
3.12 0.22 100.17 48 23
3.13 0.17 100.97 59 29
197
3.02 2.76 0 18 100.70 98 69
3 18 3.96 0.16 100.27 41 1t
3 87 3 34 0.16 100.44 33 29
373 2.51 0.14 100.66 157 59
0.32 100.82 94 25
I~kobuc~'Group
ZONE Ill bs 01
bs03
bs-02 6899 084 13.94 6.87
69 59 073 1391 6 08
0.66 357 225
0.66 346 1.71 3.94
006 3 14 189 3.49
1.11
1.98
358 2.33
0.16 101.08 225
0.16 101.03 157
0.15 101.02 190
96
66
69
3.34 2.~
Group is slightly lower than those of zones I, II and the Saroma and Nemuro Groups.
69 27 077 14 07 603 0.66 341 135
NemlAro G ~
hb 02
hb4)l
67.15 0.69 1498 591
0.16 100.69 133 62
7m 03
64.14
Nakanogawa Group ZONEII vm 05
ym 02
62.52
79 16 036 1092 396 014 15 208 117 1.14 0.05 100.48
22 20
k'w-02
)I-Ol
67.57 078 1661 578 0 O2 181 186
6986 0.65 14 15 545 006 2 57 1 68
,54 94 0.93 1767 1023 012 335 5.82
3.0~ 3.02
36 226
6.75 148
0.1~ 100.71 54
0.12 100.4
025 101.54
83
80
27
57
32
non-alkali, (2) orogenic, and (3) calcalkalic or tholeiitic basalts as summarized by Leterrier et al. (1982) (Fig. 9).
Detrital clinopyroxene composition Detrital chromian spinel composition Clinopyroxene occurs as a detrital phase in the rocks of zones I and lI (Nakanogawa Group, Hidaka Belt), and the Nemuro and Saroma Groups (Nemuro and Tokoro Belts). About 100 grains from widely spaced samples were analyzed using the electron microprobe analyzer (JEOL JCMA-733) at Hokkaido University. Selected results are presented in Table 3. These detrital grains consist mainly of augite, but also include diopside, endiopside and salite. We have used three diagrams following the discussion of Leterrier et al. (1983) (Fig. 9). They compare closely in composition with (1)
Detrital chromian spinel grains have been observed in all rocks of the Nakanogawa Group (Hidaka Belt), Nemuro Group and Saroma Group (Nemuro and Tokoro Belts). About 100 grains from widely spaced samples were analyzed using the electron microprobe analyzer (Shimazu-8705) at the Geological Survey of Japan, Hokkaido Branch. Selected results are presented in Table 4. We present two diagrams: a Cr AI-Fe s + ternary diagram and TiO2 (wt%) histogram of detrital chromian spinels (Figs. 10 and 11), and compare this data with that from the Kamuikotan metamor-
62
F. N A N A Y A M A
Discussion
1.4 1.2
o• 1.0
0
•
~0.8 o
0
o.6
A&
%
I-- 0.4
0.2 0.0
0
•
A • 0 o •
zone I (Nakanogawa Gr.) zone fl (Nakanogawa Gr.) zone III (Nakanogawa Gr.) Hakobuchi Gr. (Yezo S.G.) Saroma & Nemuro Grs.
i
i
10
15
20
FeO*+MgO (wt%) 0.4
0.3
0 A& A~3AQ~O ~] ~
0 O4
