藏南康马地区三叠系研究新进展

NEW ADVANCES IN THE STUDY ON THE TRIASSIC SYSTEM OF THE KANGMAR AREA,SOUTHERN TIBET

根据康马地区三叠系吕村组和涅如组新发现的化石及区域地质背景 ,把该区的地层时代分别厘定为中三叠世中晚期至晚三叠世早期和晚三叠世中晚期 ,并认为缺失早三叠世至中三叠世早期的沉积。研究表明康马地区三叠系与二叠系之间为微角度不整合接触 ,是“藏南运动”和“印支伸展运动”共同影响形成的。晚二叠世末至中三叠世早期 ,康马地区露出海面 ,接受剥蚀并形成喀斯特化风化壳。中三叠世末至晚三叠世 ,这一地区发生强烈伸展—裂陷 ,地壳迅速沉降 ,形成被动大陆边缘裂谷盆地 ,发育巨厚的半深海—深海复理石沉积 ,并伴随大量基性岩浆贯入。涅如组下部有两期基性岩侵入 ,早期基性岩床形成于印支晚期 ,晚期穿层侵入形成于燕山早期。

The Lucun and Nieru Formations are considered to be late Middle Triassic to early Late Triassic and Middle—Late Triassic respectively in age. Basites of the Late Triassic and Yanshan age are discovered to widely exist in Nieru Formation. An angular unconformity between Permian and Triassic widely distributed in the Kangmar area and its adjacent areas, which is considered to be the result of the joint influence of “Southern Tibet movement” and “Indisinian extensional movement”.