Accretion-Collision Tectonics of Sakhalin and Circum-Pacific Orogeny

本项目取得的成果总结如下。1)白垩纪增生杂岩，称为阿尼巴杂岩，由两个构造单元组成。上单元按升序由玄武岩、层状硅质岩、半相硅质页岩、混杂岩和陆源沉积物组成，下单元由主要的玄武岩和混杂岩组成，以丰富的石灰岩块为特征。下部单元由五个向东边缘的逆冲片组成，似乎是上部单元下方的一个底侵杂岩。2)延伸至北海道Kamuikotan变质带的Suunai杂岩是高压变质杂岩，揭示了由数十个逆冲片组成的完整的构造堆积序列，这些逆冲片由向南的低角度逆冲叠加而成。杂岩主要由绿片岩、变硅质岩、硅质片岩和与变绿泥岩伴生的变泥岩组成。根据岩性组合将该杂岩划分为五个域。例如，第四领域的特点是以玄武岩为主，上面覆盖着玄武岩沉积和黑色页岩薄层覆盖的远洋石灰岩。区分了变形的三个阶段，即d1到d3。D2应变最大、变形最强的岩石表现为NE向的非对称褶皱、NW向的鞘褶皱以及伸展和微褶皱的线理。研究区划分出两个变质带，即南部的绿帘石-安山带和北部的绿帘岩-绿帘岩-安山带。变质作用峰期的P-T条件估计为200-300Kbar C和4-5Kbar。变质作用与变形的D2相一致。3)玄武岩的主次元素组成表明，安尼巴杂岩的玄武岩具有洋岛拉斑玄武岩的特征和亲碱性，而苏苏奈杂岩的玄武岩具有N-MORB-T-MORB特征

The results obtained from this project are summarized as follows. 1) The Cretaceous accretionary complexes, called the Aniba complex, are composed of two tectonic units. The upper unit consisting of basalts, bedded cherts, hemipelagec siliceous shale, Melange, and terrigenous sediments in ascending order, thrust over thd lower the unit which is composed of dominant basalts and melanges characterized by abundant limestone blocks. The lower unit composing of five thrust sheets verging eastward, seems to be an underplating complex beneath the upper unit. 2) The Susunai complexes, high pressure metamorphic ones extending to the Kamuikotan metamorphic belt in Hokkaido, reveal a complete sequence of the tectonic pile composed of tens of thrust sheets which are stacked by low angle thrusts verging southward. The complexes consist mainly of greenschists, metachert, silicious shist, and metapelites associated with metagreywackes. The complex is divided into five domains based on lithologic assemblages. For example, Domain 4 is characterized by dominant basalts to dolerites overlain by basaltic sediments with pelagic limestones capped by a thin sequence of black shale. Three phases of deformation, D1 to D3 are discriminated. The rocks subjected the highest strain of D2, strongest deformation among them, show NE trending asymmetric folds, NW trending sheath folds and lineation of both the stretching and micro folding. Two metamorphic zones are defined in the surveyed areas, i. e. pumpellyite-actionlite zone in southern part and pumpellyite-epidote-actionlite zone in northern part. The P-T conditions at the peak of metamorphism are estimated to have been 200-300ﾟC and 4-5Kbar. The metamorphism coincides with D2 phase of deformation. 3) Major and minor element compositions of basaltic rocks exhibit that those from the Aniba complex represent oceanic island tholeiites features and alkaline affinity, whereas those from the Susunai complex reveal N-MORB to T-MORB features