西藏狮泉河—革吉一带早白垩世地层沉积环境、岩石地球化学特征及其地质意义

Petrogeochemistry and sedimentary environment of the Early Cretaceous strata from the Shiquanhe-Gegyai area in Tibet and their geological significance

通过对狮泉河—革吉一带早白垩世地层中火山岩岩石地球化学特征和沉积岩层序、沉积特征、沉积环境进行综合分析、对比,认为乌木垄铅波岩组钙碱系列火山岩的发育可能代表板块俯冲消减作用。多爱组、拖称组、朗久组构成3个不同的部分熔融系列,指示俯冲角度变陡造成的弧壳加厚的过程,而朗久组火山岩喷出的碱性特点,指示存在由于俯冲诱发的弧的拉裂。捷嘎组和郎山组是狮泉河蛇绿混杂岩带闭合后再度发生海侵、在不同大地构造位置的同一残海盆地沉积,其海盆南深北浅、东深西浅,从盆地边缘角度不整合接触向盆地内的微角度不整合-整合过渡。

Through comprehensive analysis of Early Cretaceous volcanic petrogeochemistry, sedimentary sequence, sedimentary characteristics and environment in the Shiquanhe- Gegyai area, the calc-alkaline volcanic rocks of the Wumulongqianbo Formation may represent plate subduction. The Duoai Formation, Tuocheng Formation and Langjiu Formation make up three partial melting series,indicating presence of arc crust thickening process under the condition of steepened subduction angle. The alkaline volcanic rock of the Langjiu Formation indicates subduction-induced arc crack. The sediments of the Jiega Formation and the Langshan Formation show the same residual basin under the transgression condition after closure of the Shiquanhe ophiolite mélange. The depth of the residual basin is deep in the south and shallow in the north, and deep in the east and shallow in the west. At the same time, angular unconformity occurred at the edge of the basin, which gradually evolved into weak angular unconformity- conformity towards the interior of the basin.