山西二、三叠系界线岩石地层的次生磁化及其地质意义

Remagnetization in Shanxi Area and Its Implications in the Boundary between Permian and Triassic

在太原西山剖面自上石盒子组 1段至刘家沟组底部采集定向标本 131个 ,在宁武孙家沟剖面自石千峰组至刘家沟组采集定向标本 5 8个 ,进行了古地磁学研究。逐步地层展平校正表明 ,两剖面所获得的剩磁分别为校正系数等于 0 .5和 0 .6时的次生磁化。经与公认的华北陆块古地磁学数据对比 ,前者剩磁的产生时间应为晚三叠世 ,而后者的产生时间则应为白垩纪。岩石地层次生磁化的构造地质学意义为 :晚三叠世 ,山西断块成为统一中国大陆的一部分 ;白垩纪 ,太原地区以隆升为主 ,宁武地区在隆升的同时发生岩层变形 ;新生代 ,山西断块在隆升的同时 ,中部产生断陷 ,但岩层变形不明显 ;宁武地区明显的盖层褶皱大体形成于白垩纪 ,而山西现今的地貌高度则至少来自于印支以及燕山两期构造活动的长期隆升。

Paleomagnetic characteristics were studied by testing 131 directional samples from the first part of Upper Shihezi Formation to Liujiagou Formation in Xishan section and 58 directional samples from Sunjiagou Formation to Shiqianfeng Formation in Ningwu section, Taiyuan. The results show that the residual magnetism of the two sections was remagnetization with corrected coefficients of 0.5 and 0.6 respectively. Compared with the recognized paleomagnetism data of North China Block, it is found that the remagnetization took place in late Triassic for Xishan section and Cretaceous for Ningwu section.The tectonic implications of the remagnetization are as follows:①In late Triassic, Shanxi fault block was a part of the whole Chinese continent.②In Cretaceous, the area of Taiyuan was mainly at an uplifting stage, while the area of Ningwu underwent stratigraphic deformation during uplifting.③When the Shanxi fault block was uplifting in Cenozoic, fault depression occurred in the central part, but stratigraphic deformation was not obvious.④The main mantle folds of Ningwu area were formed in Cretaceous. The present height of Shanxi area resulted from the prolonged uplifting during the Indosinian and Yanshanian tectonic formation.