塔里木盆地库车坳陷中生代盆地性状及成因分析

库车坳陷充填有厚约4000~5000 m(局部最大厚度可达6000 m)的中生界陆相地层。地面特征和地震资料表明,库车坳陷北部地区中生界与下伏强烈变形、变质的古生界呈角度不整合接触,南部地区中生界与下伏寒武系-奥陶系呈平行不整合或微角度不整合接触。按照地层厚度趋势推测的中生界在山前地带有强烈的剥蚀,沉积厚度轴线位于南天山晚古生代造山楔之上,显示库车坳陷中生代盆地是上叠在塔里木克拉通北部边缘隆起和南天山晚古生代造山楔过渡带上的拗陷盆地。三叠纪-侏罗纪沉降-沉积中心向后陆(造山带)迁移,早白垩世向前陆迁移,且盆地同沉积期区域规模的断裂活动不明显,据此推测晚古生代造山作用后的岩石圈热作用及地壳均衡作用是中生代盆地沉降的主控动力学因素。

Characteristics of Mesozoic Basin in Kuqa Depression,Tarim Basin

The Kuqa Depression is filled by the Mesozoic terrestrial sediments with a thickness of 4000-5000 m and can be up to 6000 m thick locally.On the geological outcrops at the northern margin of the depression,the Mesozoic strata angular unconformaly overlie the strongly deformed and metamorphosed Paleozoic sequences.On the contrary,at the southern part of the depression,contact between the Mesozoic strata and the Cambrian-Ordovician System is paraconformity.The thickness tendency of the residual Mesozoic strata indicates that the subsidence-deposition axis was situated on the frontier of the South Tianshan fold-thrust belt,and therefore it is speculated that the Mesozoic basin of the Kuqa Depression is a flexure depression superimposed upon the transition zone between South Tianshan Late Paleazoic fold-thrust belt and north marginal uplift of Tarim Craton.The thickness axis migrated to the hinterland from Triassic to Jurassic,but migrated to the foreland during the Early Cretaceous,and no regional fault was active during Mesozoic.Base on comprehensively analyses of basin structure,it is inferred that the thermal dynamic and isostasy of post-Late Paleazoic Orogeny could be the controlling factors for the basin subsidence.