西藏日喀则地区恰布林组物源分析

PROVENANCE ANALYSIS OF THE GIABULIN FORMATION IN XIGAZE, XIZANG (TIBET)

长期以来，沿西藏雅鲁藏布江南岸呈东西向展布的恰布林组砾岩，被认为是造山期后磨拉石的产物，而被置于第三纪。由于在屯穷紫色泥岩底部灰绿色粉砂质灰岩中发现腹足类化石Ｋａｔｏｓｉｒａｓｐ．，并结合其他地质证据，可以确定该组时代属于早中侏罗世。结合岩石学特征、典型砾岩中砾石的岩石地球化学和物源区分析表明，恰布林组砾岩的砾石有相当一部分来自蛇绿岩，其特征明显不同于现今的雅鲁藏布江蛇绿岩。因此认为雅鲁藏布江存在早中侏罗世之前的古蛇绿岩。

It has been accepted for a long time that the Giabulin Formation conglomerate along the southern bank of Yarlng Zangbo River is the product of the post-orogenic molasse and belongs to the Tertiary Period. The Giabulin Formation must belong to the Early-Middle Jurassic Epoch according to the fossil of gastropod, Katosira sp., which is discovered aming the calcarenite at the bottom of the Tunqiong purple mudstone and to the other geological evidences. The Giabulin Formation conglomerate mostly came from ophiolite by analyzing the petrological character,typical lithogeochemlstry and its provenance, but its character differs apparently from the recent Yarlng Zangbo River ophiolite. From above, this paper deems that the palaeo-ophiolite prior to Early-Middle Jurassic exists in Yarlng Zangbo River.