Comparative petrologic study of ophiolitic rocks in the Japanese Islands and Russian Far East

(1)在日本的研究。出露在神谷里地区的雅库诺蛇绿岩西段构成了晚古生代大洋岛弧的地壳剖面。变质角闪岩中富钙斜长石和富铁单斜辉石的共存，以及角闪岩中高度亏损的不相容微量元素的存在，支持这一鉴定，这一点也被玄武岩的发现所证实。我们测定了小山蛇绿岩中角闪石的K-Ar年龄，确定了其早古生代年龄(400-440 Ma)。我们在尾密地区的仁格蓝片岩带中发现了榴辉蓝闪片岩。这一发现证明，仁格变质作用已达到榴辉岩相。在青森县北上带侏罗纪增生杂岩中，发现增生的火山岩(绿岩)大多为洋岛拉斑玄武岩成因。这与岩手县南部地区以绿岩为主的碱性玄武岩成因形成了鲜明的对比，证明了海山的岩浆多样性。(2)俄罗斯研究。科里亚克山脉南缘泰戈诺斯半岛的Elistratova蛇绿岩具有独特的产状，岛弧蛇绿岩层序侵入大洋地幔橄榄岩。泰戈诺斯半岛东海岸地幔橄榄岩的亏损程度也存在着极大的差异性。在Primorye，我们发现寒武纪坎卡蛇绿岩具有明显的“被动大陆边缘”产状，与锡霍特-阿林增生系统中的其他早古生代“增生”蛇绿岩明显不同。我们对伴生蓝片岩的岩石学和年代学研究表明，日本的Oeyama蛇绿岩-仁格蓝片岩对与Primorye的早古生代蛇绿岩-晚古生代蓝片岩对有密切的相似之处。

(1) Research in Japan. Western part of the Yakuno ophiolite exposed in the Kamigori area constitutes a crustal section of the late Paleozoic oceanic island arc. The coexistence of Ca-rich plagioclase and Fe-rich clinopyroxene in the metagabbro as well as highly depleted incompatible trace elements in amphibolite support this identification, which is also confirmed by the finding of shoshonitic rocks. We measured K-Ar age of hornblende from metacumulates of the Oeyama ophiolite, and confirmed their early Paleozoic age (400-440 Ma). We find eclogitic glaucophane schist from the Renge blueschist belt in the Omi area. This finding proves that the Renge metamorphism reached the eclogite facies. In the Jurassic accretionary complex of the North Kitakami belt in Aomori Prefecture, we find that the accreted volcanic rocks (greenstones) are mostly of ocean-island tholeiite origin. This clearly contrasts to the reported alkali basalt origin, which predominates greenstones in the southern Iwate Prefecture area, and proves magmatic diversity of the accreted seamounts.(2) Research in Russia. The Elistratova ophiolite in Taigonos Peninsula at the southern edge of the Koryak Mountains shows peculiar occurrence, where a stratified sequence of an island-arc ophiolite intrudes into the oceanic mantle peridotite. Extreme diversity in the degree of depletion of mantle peridotite along the eastern coast of Taigonos Peninsula is also revealed. In Primorye, we find that the Cambrian Khanka ophiolite shows distinct "passive continental margin" occurrence clearly different from the other "accretionary" early Paleozoic ophiolites in the Sikhote Alin accretionary system. Our petrologic and geochronologic study of the associated blueschist revealed close analogy between Oeyama ophiolite-Renge blueschist pair in Japan and the "accretionary" early Paleozoic ophiolite-late Paleozoic blueschist pair in Primorye.