Banno Shohei

Enami Masaki

Iwata Osamu

Kasashima Seiei

Nakamura Kenji

Yokohama Kazumi

板野 昇平

榎並 正樹

中村 健二

笠嶋 晴英

Kanazawa University Repository for Academic Resources

Sci. Rep.区anazawaUniv. Vo1. 21， No. 2， pp.139-159 December 1976 Petrography of the perido“ti抗te.幽由幽幽幽幽幽幽i加nthe vicinity of Mt. Higashi-akaishi， Central Shikoku. Part I. Megascopic textures of the Iratsu and Tonaru epidote amphibolite masses Shohei BANNO， Kazumi YOKOYAMAへMasakiENAMI， Osamu IWATAぺKenjiNAKAMURA and Seiei KASASHIMA De仰rtment01 Earth Sciences， Kanaza仰 Universi.机 Kanaza仰 920(Received September 30， 1976) Abstract The megascopic textures of the constituent rock-types of the Iratsu and Tonaru epidote amphibo1ite masses are described. The emphasis is put on the textures suggestive of gabbro origin of the masses. Introduction After a long period of dispute on the origin of the epidote amphibolite or "amphi-bolite" masses situated in the Sanbagawa metamorphic terrain in central Shikoku， itbecame general1y agreed that they are metamorphosed gabbros (cf. Banno et al.， 1976). The reasoning in support of this idea varies by different investigators and includes an intimate association of Mt. Higashi-akaishi peridotite and neighbouring epidote amphibolite masses (Shibata， 1972)， and the presence of rocks with granulitic and gabbroic or flaser gabbroic textures (Shiraishi， 1975). In addition to these evidences， Banno et al. (1976) have emphasized the significance of the layers of zoisite-rich rock or zoisitite which is mainly composed of zoisite (and clinozoisite) and measures in maximum 6 meters thick， because its bulk chemistry appears to be nothing but of anorthosite in layered gabbro. Further， we often find structures suggestive of relic igneous graded bedding in massive parts of the Iratsu mass. If zoisite-and clinozoisite-rich layerwere derived from anorthosite and plagiocla-se-rich gabbro， we can restore the texture of original gabbro from the pattern of the distribution of white zoisite-or clinozoisite-rich part and dark hornblende-rich part， the laUer being derived from pyroxene-rich gabbro， inoutcrops and in hand specimens. In this way， we can recognize anorthosite， pegmatitic gabbro and gabbro as wel1 as the * Geological Institute， University of Tokyo， Hongo， Tokyo 13 柿 KanayamaJunior Highschool， Kanayama， Gifu 509-16 139-140 Shoh日 BANNO，Kazumi YOKOYAlVlA， Masaki ENAMI， Osamu IWATA， Kenji NAKAlVlURA呂ndSeiei KASASHlMA ????? 直皿 Hi日目shi-akaishi い止lULII 問ridotitem口55比三三ヨ lratsu epidot母一|ヒ二二二ゴ 口mphibolitem口55![7:7穴0! Ton口ru官pidote-じ:::LLLJ口mphibolitemass 。題担盟副5km E霊彊彊亙二三ごコFig. 1. lndex map of the Iratsu and Ton呂ru印idoteamphibolite masses. gradation of the structure from layered gabbro to gneissose and schistose amphibolite. The main purpose of this paper is to present photographs of outcrops and hand specimens in order to show that the most widespread rock-types of these masses were derived from layered gabbro. The megascopic textures of the and its chemical characteristics offer the most conclusive evidences to estimate the nature of the original rocks， because the majority of the constituent minerals is of the epidote amphibolite facies and the metagabbro suffered granulite facies matamorphism prior to the Sanbagavva metamor-phism (Yokoyama and Mori， 1975， and Yokoyama， 1976). We have as yet not confirmed the minerals of primary gabbro in the specimens of the masses in question. Although the bulk rock chemistry is a clue to decipher the original rock-types of the masses， itis not described in this paper. Interested reader may refer to Banno et al. which describes the chemistry of major rock-types. A more detai!ed table we will be availab!e in a paper being prepared by Y okoyama. M母gascopIctextures of th喧 epidoteamphiboiite mass配昌The megascopic textures of the major rock-types of the Iratsu and Tonaru epidote amphibolite masses are described in this chapter in terms of photographs of outcrops and hand specimens. The locations of the valley and mountain refered in the text are shown in Fig.L Unless otherwise noted， the measures in the photographs are 1 meter long， with minimum 1 mm scale and numbers at every 1 centimeters. Petrograjうhyojthe μridotite-metagabbro complex in the viciniかq川4t.Higashi-a初ishi，Central Shi.知的. 141 References BANNO， S.， K. YOKOYAMA， O. IWATA and S. TERASHIMA， 1976， Genesis of epidote amphibolite masses in the Sanbagawa metamorphic belt of Central Shikoku (in Japanese with English abstract). Jour. Geo1. Soc. Japan， Vo1. 82， 199-210. SHIBATA， T.， 1972， On the occurence of anhydrite in the Iratsu ultramafic complex， Central Shikoku. J our. J apan. Assoc. Petr・.Min. Econ. Geo1.， Vo1. 67， 76-83. SHlRAISHl， K.， 1975， Amphibolite and Ultramafic Rocks in Futatsudake， Ehime Prefecture (in Japanese). Jour. Geo1. Soc. Japan， Vo1. 81， 53-54. YOKOYAMA， K.， 1976， Finding of plagioc1ase-bearing ganulite from the Iratsu epidote amphibolite mass in Central Shikoku. Jour. Geo1. Soc. Japan， Vo1. 82，549-552. YOKOYAMA， K. and T. MOR~ 1975， Spinel-gamet two pyroxenes rock from the Iratsu epidote amphi. bolite mass in Central Shikoku. Jour. Geo1. Soc. Japan， Vo1. 81， 29-37. 142 Plate 1 Zoisite寸'ichJrllcks: The rock consists mainly of zoisite and is always accom-panied by quartz. Kyanite and paragonite are the common accessories. Other constituent minerals arεhornblende and garnet. Chemically， this rock-type corr巴spondsto anorthosite. A: An outcrop in the Nikubuchi val!ey. Th巴 verticalsize of photograph is approximately 6 meters Thin homblend日 richlayers are intercalatεd B: An outcrop in the Nikubuchi valley， showing a paral1el alignment of dark homb!ende-rich and whit巴zoisite-richlayers C: 5teαmeη P-l A hand specimen of hornblendεbearing kyanite-zoisite rock， coil思ctedfrom the Nikubuchi valley. 143 PLATE 1 A B C 144 Plate I. Gabbro pegmatite: The size of white and dark portions and the texture suggest that these rocks were derived from gabbro pegmatite. All samples were collected from th巴Nikubuchivalley. A: Specimen P-7 Whit巴 partconsists of zoisite with subordinate amount of c1inozoisite， albite and quartz， and dark part of coarse-grained c1inopyroxene partly replaced by homblende along c1eavages and grain .boundaries. Another minor constituent is rutile B: Sβecimen P-8 White part: c1inozoisite with subordinate chlorite， dark part: mainly homblende. C: 訪問押wnP-2 White part: c1inozoisite， dark part: pyroxene partly replaced by homblende. White part in the upper part of the rock consists of grossular and zoisite. ??? ? ? ?」?B C 145 PLATE I 146 Plate II. In the Nikubuchi valley， wherεoutcrops shown in this plate occur， clinozoisite amphibolitεoften preserves gabbroic appearence， although the mineralogy is mainly of epidote amphibolite facies A: Gabbroic appearence of clinozoisite amphibolite B: Homogeneous but fo¥iated clinozoisite amphibolite， Clinozoisite-rich facies C: Coarse-grained gabbro pegmatitic part D: Coarse-grained garnet in clinozoisite amphibolite， 147 PLATE II 148 Plate IV The majority of 邑pidoteamphibolite masses is composed of schistose or gneissose clinozoisite amphibolite， which consists of the alternation of clino-zoisite-rich and hornblende-rich layers， each measuring 10 to 30 cm thick Photographs shown in this plate w巳retaken at outcrops along the Kokuryo river， where the Tonaru mass is exposed. A， B， C: Banding of clinozoisite amphibolite. White layer in C is albiti旬。A 149 PLATE IV B 150 Plate v. Close up view of schistose clinozoisite amphibolite. A: An outcrop along th日Kokuryoriver. The Tonaru mass B: Polished surface of a hand specimen coll日ctedfrom Nikubuchi valley， the Iratsu mass. Garnet porphyroblasts are surrounded by dark homblende rim. C: A block in the Nikubuchi valley， the Iratsu mass. 151 PLATE V ヤ152 Plate VI Folding of banded clinozoisite amphibolite of the Tonaru mass， Thεphoto graphs were taken at outcrops of the Kokuryo river 153 PLATE VI 154 Plate VII. Polished surfaces of hand specimens coll巴ctedfrom the Iratsu mass. A: S戸Eαme月 P-3 Banding of clinozoisite呂mphibolite. White layer is composed 。fclinozoisite and subordinate hornblende， dark layer mainly of horblende and the central grey one consists of garnet and hornblende， Nikubuchi valley. B: S'jJecimen P-5 Gneissose texture consisting of white elongated patches (white mica and clinozoisite) and dark matrix with hornblende and clinozoisite. Nikubuchi valley. C: Steαme日 P-lO Quartz eclogite collected from Mt. Gongen. D乱rkco呂rsegrained part is garnet and white p呂rtconsists of quartz and muscovite. Grey matrix consists of quartz and omphacite. Hornblende occurs replacing garnet and omphacite D: Stecimen P-4 Gneissose texture of folded clinozoisite amphibolite. Dark part contams garnεt and hornblende with subordinate clinozoisit巴. Northεrn slope of Mt. Futatsudake. 155 PLATE VII 2Omm A B C D 156 Plate VIII R巴licigneous graded bedding， originally forrned by differential settling of pyroxen邑 andplagioclase， isnow observ巴dby the on巴directionalchange of th巴rnode of arnphibole， frorn hornblende-rich to clinozoisite-rich arnphibolites A: Y ounging upwards. Each cycle starts frorn hornblends-rich clinozoisite arnphibolite and gradually changes to clinozoisite-rich arnphibolite and is abruptly terrninated being covered by dark arnphibolite. Nikubuchi vall巴yB; Close up view of graded bedding in an outcrop close to but different frorn that of A. Nikubuchi valley C; 51うωmenP-6 A hand specirnen showing the contact between two units of grading. N ikubuchi valley A 20mm t二二軍園田4C 157 PLATE VIII B 158 Plate IX. Mode of occurence of some unusual rock types A: Pegmatitic gabbro in the Nikubuchi peridotite mass. Layer of 5 cm thick consisting of hornblende with or without relic pyroxene and zoisite occurs in peridotite. Nikubuchi valley. B: Two pyroxenes granulite enclosed in garnet-c1inozoisite amphibolite. The granulite consists of aluminous ortho-and c1inopyroxenes and anorthite (An 90)， th巴lastmineral is partly replaced by the aggregate of zoisite + kyanite + quartz. Mineralogy of the granulite is described in Y okoyama (1976) C: A limestone layer in the Tonaru mass. The 1im巴stoneis concordant to the fold structure of the epidote amphibolite. An outcrop along the Kokuryo river A 159 PLATE IX 

Petrography of the peridotite-metagabbro complex in the vicinity of Mt. Higashi-akaishi, Central Shikoku. Part I. Megascopic textures of the Iratsu and Tonaru epidote amphibolite massas

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Petrography of the peridotite-metagabbro complex in the vicinity of Mt. Higashi-akaishi, Central Shikoku. Part I. Megascopic textures of the Iratsu and Tonaru epidote amphibolite massas

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