Abstract

The Siang valley in the eastern part of Arunachal Himalaya contains Paleocene–Eocene sediments of Yinkiong Group along with the Abor volcanic exposed in a wide lateral extent in the middle and lower Siang valleys. Based on available geologic data and detail geologic mapping present study proposes a new evolution model of the basin in the context of India–Asia collision tectonics. Integration of the field data on the disposition of different litho units from Pasighat (south) to Tuting (north) along the Siang valley and in the Mishmi block, helped us to constrain several major thrust fault and strike-slip faults in the area showing dextral and sinistral senses. Some of these faults are conjugate. It is postulated that during the early Paleocene, the Indian Plate collided with the Eurasian Plate and this collision resulted in the breakage of an edge of the Indian Plate along its northeastern extremity. This broken edge rotated towards the Burmese Plate and eventually formed a rift basin that led to the ingress of the Tethys Sea where sedimentation along with syn-sedimentary volcanism took place. The sedimentation in the basin continued throughout the Paleocene–Eocene time. The absence of rocks younger than Yinkiong Group indicates that this basin was closed at the end of the Eocene. The development of a highly folded sequence along the Siang valley in response to north south-directed compression can be constrained due to subsequent India‒Asia collision. The broken edge of the Indian Plate and western part of the Burmese Plate amalgamated through Tuting–Tidding suture. This Indo-Burmese amalgamated part of the Mishmi block thrusted over the Paleocene–Eocene sequence from the east. The continued NNW ward movement of the Mishmi block resulted in the swinging of the MCT towards the northeastern direction. On the other hand, the overriding of the Himalayan metamorphic belt along the Tidding Thrust was intense, leaving only a narrow exposure of garnetiferous graphite-schist and garnetiferous amphibolites as slivers of the ophiolite package. The Lesser Himalayan sequences of the Mishmi block overrode the frontal molasses basin in many places and are in direct contact with the Brahmaputra alluvium in the southeastern part along the Lohit and Dibang valleys. The Lesser Himalayan sequence also overrode the Paleocene–Eocene sequence from the western direction showing significant occurrences in the Boleng and Bomdo area of the Siang valley.

中文翻译：

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喜马拉雅东部银孔群和亚伯火山岩的地质构造演化：地质资料概述

摘要

阿鲁纳恰尔喜马拉雅山东部的Siang山谷包含Yinkiong群的古新世-始新世沉积物，以及在Siang中下游山谷广泛暴露的Abor火山。基于现有的地质数据和详细的地质图，本研究提出了一个在印度－亚洲碰撞构造背景下的盆地演化新模型。沿实谷和Mishmi区块整合了从Pasighat（南部）到Tuting（北部）不同岩石单元位置的野外数据，帮助我们限制了右旋地区的几个主要逆冲断层和走滑断层和左派的感官 其中一些故障是共轭的。据推测，在古新世初期，印度板块与欧亚板块相撞，这种碰撞导致印度板块沿其东北端的边缘断裂。断裂的边缘转向缅甸板块，并最终形成了一个裂谷盆地，导致特提斯海进入，在那里沉积和同沉积的火山作用一起发生。在整个新世-始新世期间，盆地中的沉积持续进行。没有比Yinkiong Group更年轻的岩石，表明该盆地在始新世末期是封闭的。由于随后发生的印度-亚洲碰撞，可能会限制沿Siang山谷沿南北向压缩形成的高度折叠序列。印度板块的断裂边缘和缅甸板块的西部部分通过图丁－平缝缝合线合并在一起。Mishmi区块的印度-缅甸融合部分从东部冲入古新世-始新世序列。Mishmi街区不断的NNW病房移动导致MCT向东北方向摆动。另一方面，喜马拉雅变质带沿潮汐冲断带的压倒作用很强烈，仅少量暴露于蛇绿岩片岩中的石榴石石墨片岩和石榴石闪石。Mishmi区块的小喜马拉雅层序在许多地方都覆盖了正面的糖蜜盆地，并且与东南部的Lohit和Dibang谷地的Brahmaputra冲积层直接接触。