J. Japan. Assoc. Min. Petr. Econ. Geol. 80, 13-20, 1985

Finding of olivine- and garnet-bearing biotite quartz norite from the Hidaka metamorphic belt, Hokkaido, Japan*

JIN'ICHIROUMAEDA1, NOBUTAKA TSUCHIYA1, KAZUNORI ARITA1, YASUHITOOSANAI1, SHIN'ICHI SUETAKE1, YASUO IKEDA1 , MITSUTAKABAMBA2 and MASAAKIOWADA2 Departmentof Geologyand Mineralogy,Faculty of Science, HokkaidoUniversity, Sapporo 060, Japan Departmentof Geologyand Mineralogy,Faculty of Science, NiigataUniversity, Niigata 950-21, Japan

We found olivine- and garnet-bearing biotite quartz norite from the upper stream of the

Niobetsu River of the southern Hidaka Mountains. Until now no peraluminous igneous rocks

have been reported from the Main Zone of the Hidaka metamorphic belt except migmatitic rocks . Garnets of the norite are similar in composition to those from dacites and rhyolites. Orthopyrox enes contain 1.0-2.3 wt% Al2O3 and 0.2-0.5 wt% CaO, resembling those in peraluminous igneous

rocks. The texture, mineralogy and other evidence suggest that the norite crystallized from a

peraluminous magma at 940-1070•Ž and 4-5kbar.

petrochemical characteristics of the S-type I. Introduction granite (Maeda et al., 1981; Komatsu, 1983). The Hidaka metamorphic belt is composed The plutonic rocks are gabbro, diorite and of two distinct zones: the Western Zone being granite of the calc-alkalic series, gabbro and considered as an oceanic type crust, and the ferrogabbro of the tholeiitic series, and a small Main Zone as a continental type crust (Koma amount of quartz monzonite of the alkalic tsu et al., 1983). The Main Zone consists of series (Maeda et al., 1981). Most of these various metamorphic rocks of the greenschist rocks have no magnetite, and belong to the to granulite facies, migmatites, and plutonic ilmenite-series (Ishihara, 1977; Maeda et al., rocks. 1981). Isotopic studies on the plutonic rocks The metamorphic rocks decrease in grade (Shibata and Ishihara, 1979; Sasaki and Ishi from the granulite facies in the west to the hara, 1979; Okamoto and Honma, 1983; Taka greenschist facies in the east. Large bodies of hashi and Sasaki, 1983) indicated an influence of biotite migmatite often including cordierite sedimentary rocks on the genesis of the occur in the amphibolite and greenschist facies plutonic rocks. zones, while small masses of hypersthene-gar Besides migmatitic rocks, no peraluminous net migmatite are found in the granulite zone (Al>2Ca+Na+K) igneous rocks have been (Komatsu et al., 1982; Komatsu, 1983). Most reported from the Main Zone of the Hidaka of the migmatites show mineralogical and metamorphic belt. During the field work in

(Manuscript received, June 11, 1984; accepted for publication, October 30, 1984) * Contribution from the Nozukadake Research Group, No. 1. 14 J. Maeda et al.

II. Mode of occurrence The garnet norite crops out in the upper stream of the Niobetsu River of the southern Hidaka Mountains (Fig. 1). In the outcrop, the garnet norite intrudes into orthopyroxene-gar net-cordierite-biotite gneiss and displays chilled margins against the country rock. On the eastern and western sides of the outcrop, cordierite-biotite migmatite and hornblende olivine norite, respectively, are extensively exposed (Fig. 2). Cordierite-biotite migmatite and biotite gneiss are also sporadically included in the hornblende-olivine norite. The relation ships between the migmatite and the gneiss, and between the garnet norite and the hornblende Fig. 1. Index map showing the locality of the olivine norite are uncertain because of paucity Nozukadake garnet norite (the topo of outcrop. graphical map after Geographical Survey Institute of Japan). Enclosed area corre sponds to Fig. 2. III. Petrography The garnet norite is dark gray, coarse 1983, we found a small outcrop of olivine- and grained, and massive. It includes occasionally garnet-bearing biotite quartz norite (hereafter small lenticular xenoliths of biotite gneiss (Fig. abbreviated as garnet norite) in the Nozukada 3B). Under the microscope, the garnet norite ke area of the Main Zone. It is likely that this shows subhedral granular texture (Fig. 3A). garnet norite originates from a peraluminous The garnet norite has no sign of deformation in magma. Its mode of occurrence, petrography contrast to the intensively deformed country and mineralogy will be described here with a rock. The main constituent minerals are orth preliminary discussion on its origin. opyroxene, plagioclase, quartz, biotite, garnet, and olivine. Apatite, zircon, ilmenite,

Fig. 2. Route map around the outcrop of the Nozukadake garnet norite. Cordierite-biotite mig matite and orthopyroxene-garnet-cordierite-biotite gneiss are put together for simplicity. Garnet norite from Hidaka metamorphic belt 15

Fig. 3. Photomicrograph of the Nozukadake garnet norite, O1, olivine; Op , orthopyroxene; Gt, garnet; Bt, biotite; P1, plagioclase; Gr, grunerite; Inc, inclusion of biotite gneiss. Scale bar, 5mm for A and 1mm for B.

pyrrhotite and chalcopyrite are also included as always enclosed in orthopyroxene (Fig. 3B). accessory minerals, but magnetite is absent. Biotite (X=pale yellowish brown, Y=Z=

Garnet is euhedral to subhedral, ranging from 4 dark reddish brown) and quartz fill the inter to 20mm in size, and frequently contains euhe stices among garnet, orthopyroxene and plagio dral apatite and in places subhedral orthopy clase. roxene and plagioclase. Orthopyroxene (X= Modal composition of a thin section of the pale green, Y=pale green, Z=pale pink) is garnet norite is as follows: plagioclase 22.6% subhedral to anhedral. It is commonly re (vol.), olivine 0.3%, orthopyroxene 16.3%, gar placed by secondary grunerite (X=pale green net 17.9%, biotite 5.1%, quartz 9.2%, apatite ish brown, Y=pale brown, Z=pale brown), 1.0%, opaque minerals 1.0%, zircon trace which is further replaced by an unidentified amount, and secondary minerals 26.4% (gruner amphibole (X=pale bluish green, Y=bluish ite 25.8%, pale bluish green amphibole 0.6%). green, Z =green) at the margin. Orthopyrox Modal composition of garnet on a large pol ene often displays very thin exsolution lamellae ished sample (40•~40cm) is 3.8%. of Ca-rich clinopyroxene (Bushveld type). Plagioclase is euhedral to subhedral and shows IV. Mineral chemistry zonal structure. Olivine is highly resorbed and Selected analyses of the main constituent

* XFe=Fe/(Mg+Fe). 16 J. Maeda et al.

CaO contents of olivines are very low and Table 1. Selected analyses of the main con stituent minerals from the Nozu scarcely detected by electron probe microana kadake garnet norite lyzer. Orthopyroxenes contain 1.0-2.3 wt% A1203 and 0.2-0.5 wt% CaO. Plagioclases range An31-An46. Garnets are rich in FeO and poor in MnO (almandine79-86spessartine2-4 pyrope6-12grossular5-6). Weak compositional zoning increasing in almandine and decreasing in pyrope is observed at the margin, but spessartine and grossular remain almost con stant.

V. Discussion Asai (1956) reported a boulder of " plagio clase-garnet-hypersthene-hornblende rock " from the Niobetsu River. He mentioned that the rock may be of a metasomatic origin. The Nozukadake garnet norite differs from the rock reported by Asai in the presence of olivine and the absence of hornblende, green spinel and magnetite. Garnets, orthopyroxenes, and biotites in

* Total iron as FeO. the garnet norite are richer in iron than those in 01, olivine; Op, orthopyroxene; Gt, garnet; the surrounding orthopyroxene-garnet-cordier Bt, biotite; P1, plagioclase. ite-biotite gneiss (garnet almandine69-73 spessartine5-6pyropel8-22grossular3-4, minerals in the garnet norite are listed in orthopyroxene XFe=ca.0.57, and biotite XFe= Table 1. The mafic minerals are rich in iron 0.52-0.56). The garnets in the surrounding content: olivine XFe*=0.87-0.93, orthopyrox rock include no apatite in contrast to those in ene XFe=0.62-0.81, and biotite XFe=0.76-0.81. the garnet norite. Therefore, the garnets, as

Table 2. Pressure-temperature conditions calculated by means of Thompson's geothermometer and Newton and Perkins' geobarometer

P1 and P2 are calculated at temperature of 940•Ž and 1070•Ž, respectively. XAMg, XAFe, aAB, and KD refer to Mg/

(Mg+Fe) in phase A, Fe/(Mg+Fe) in phase A, activity of B in phase A, and (XBtMg/XBtFe)/(XGtMg/XGtFe), respectively. Garnet norite from Hidaka metamorphic belt 17

Fig. 4. Fe-Mg-Mn-Ca diagram showing chemical compositions of garnets from various types of igneous rocks; andesites (open circle), dacites and rhyolites (small solid circle), and granites, aplites and pegmatites (open triangle). The source of data is given in References. Garnets from the Nozukadake garnet norite are represented by large solid circle in the right inset figure.

well as other constituent minerals, in the garnet of evidence: 1) the garnets are commonly euhe norite may not be xenocrysts derived from the dral crystals with no reaction rims, 2) they

surrounding metamorphic country rock. include apatites, orthopyroxenes and plagio

The solidification conditions of the garnet clases which are thought of as magmatic miner

norite are estimated using the garnet-biotite als, and 3) the temperatures estimated from the

geothermometer (Thompson, 1976) and the gar garnet-biotite pairs are too high for a net-orthopyroxene-plagioclase geobarometer metamorphic origin. Magmatic garnet is one

(Newton and Perkins, 1982) (Table 2). The of the characteristic minerals of peraluminous results showed 940-1070•Ž and 4-5 kbar. igneous rocks (Clarke, 1981).

Magmatic garnet is rarely found in inter Orthopyroxenes are one of the common

mediate to acidic igneous rocks. Fig. 4 shows constituent minerals in both peraluminous and

the substitutional relation of garnets from metaluminous (Na+K

different igneous rock types, i.e. andesites, igneous rocks. According to Nozukadake

dacites and rhyolites, and granitic rocks. The Research Group (in preparation), orthopyrox

compositions of the garnets in the garnet norite enes from peraluminous and metaluminous

resemble those from dacites and rhyolites. rocks crystallized under the crustal conditions

The garnets in the garnet norite are proved to are distinguished from each other by the chemi be of a magmatic origin by the following lines cal compositions. Orthopyroxenes from 18 J. Maeda et al.

metaluminous rocks have a wide range of XFe kadake garnet norite differ from each other in

(ca. 0.1-0.8) and those from peraluminous rocks chemical composition (Komatsu, 1983; Nozu are rather restricted to be iron-rich (XFe•†0.4). kadake Research Group, unpublished data) and

In the range of XFe•†0.4, orthopyroxenes from mineral paragenesis, the peraluminous feature

peraluminous rocks have Al2O3•†1.0 wt% and of both the rocks is worth noting in elucidation CaO•…0.6%, and those from metaluminous of the geneses of other migmatites and granites

rocks have A12O3 •…1.0% and CaO•†0.6. These found in the amphibolite and greenschist facies differences are mainly attributed to the zones of the Main Zone. differences in the chemical composition of The petrogenesis of the Nozukadake gar magmas from which orthopyroxenes crystal net norite and its genetic relations to the sur

lized (Nozukadake Research Group, in prepara rounding rocks, hornblende-olivine norite and

tion). Orthopyroxenes of the Nozukadake cordierite-biotite migmatite, will be discussed

garnet norite are rich in XFe (0.62-0.81), and in detail in a separate paper. contain 1.0-2.3 wt% A12O3 and 0.2-0.5 wt% VI. Concluding remarks CaO, showing the characteristic features of

orthopyroxene from peraluminous igneous The conclusions we draw from this work

rocks. are:

Bulk chemical compositions of coarse 1. Olivine- and garnet-bearing biotite quartz

grained plutonic rocks, such as the Nozukada norite was found from the Main Zone in the ke garnet norite, may not always represent the southern Hidaka metamorphic belt;

compositions of magmas. It is, therefore, 2. The norite crystallized from a per

difficult to judge whether the magma from aluminous magma at 940-1070•Ž and 4-5 kbar.

which the Nozukadake garnet norite crystal

lized is peraluminous or not in terms of its bulk Acknowledgements: We thank Prof. Y.

composition. However, the presence of mag Katsui of Hokkaido University for critical

matic garnet and the chemical features of reading and improving of the manuscript, and

orthopyroxene strongly suggest that the Nozu Profs. S. Hashimoto and K. Yagi of the same

kadake garnet norite crystallized from a per university for continuous encouragement.

aluminous magma. A similar mineral assem Thanks are due to Drs. M. Komatsu of Niigata

blage to that of the Nozukadake garnet norite, University, K. Niida and S. Miyashita of Hok

plagioclase-olivine-orthopyroxene-garnet, was kaido University, M. Ogasawara of Geological also reported from the peraluminous Toombul Survey of Japan, and M. Murata of Tohoku

lup rhyodacite (Birch et al., 1977). University, and two anonymous reviewers for

Komatsu (1983) reported a peraluminous critical comments, and to Mr. K. T. M. Johnson

rock (hypersthene-garnet migmatite) from the of Hokkaido University for a critical reading of

Pankenushi River of the Main Zone of the the manuscript. Gratitude is extended to the

northern Hidaka Mountains, and considered it members of the Hokkaido Tectonics Research

to be formed by anatexis under the conditions Group. We are also grateful to Profs . M.

of garnulite facies. The hypersthene-garnet Shimazu of Niigata University and Y . Kato of migmatite differs from the Nozukadake garnet Ryukyu University for providing facilities for

norite in the presence of cordierite and K-feld microprobe works, and to Messrs . K. Mori spar and the absence of olivine. Although the bayashi and T. Kuwajima of Hokkaido Uni

hypersthene-garnet migmatite and the Nozu versity for preparing thin sections . Garnet norite from Hidaka metamorphic belt 19

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日高変成 帯か らのカ ンラン石ザ クロ石含有黒雲母石英 ノー ライ トの発見

前田仁一郎 ・土谷 信高 ・在田 一則 ・小山内康人 末武 晋一 ・池田 保夫 ・番場 光隆 ・大和田正明

日高 変 成 帯 南 部 の ニ オ ベ ツ川 上 流 で 標 題 の 岩 石 が 発 見 され た 。 日高 変 成 帯 主 帯 で は,こ れ ま で,ミ グ マ タ イ ト類以 外 に は パ ー ア ル ミナ ス な岩 石 は 見 つ か って い な い 。 この ノー ラ イ ト中 の ザ ク ロ石 は デ イ サ イ ト

や 流 紋 岩 中 の もの と組 成 が 類 似 し て い る。 斜 方 輝 石 のA1203, CaO量 は各 々, 1.0-2.3%, 0.2-0.5%であ り, パ ー ア ル ミナ ス な 火 成 岩 中 の もの に類 似 し て い る。 岩 石 組 織 や 鉱 物 の組 成 な ど の 根 拠 か ら ,こ の ノ ー ラ イ トはパ ー アル ミナ ス な マ グ マ か ら940-1070℃,4-5kbarの 条 件 下 で 晶 出 した と考 え られ る。