Origin, Age and Significance of Pseudotachylites from the Eastern Dabieshan Orogenic Belt, China  

作　　者：LIUJianmin DONGShuwen ZHANGJiasheng LIUXiaochun CHENBailin 

机构地区：[1]InstituteofGeomechanics,CAGS,Beijing100081 [2]InstituteofGeology,ChineseSeismologicalBureau,Beijing100029

出　　处：《Acta Geologica Sinica(English Edition)》2004年第1期52-60,共9页地质学报（英文版）

基　　金：the National Natural Scicnce Foundation Grant 40172077 ;the Regional Geological Survey,CAGS,DKD2001009.

摘　　要：Recent field survey in the eastern Dabieshan Mountains has revealed extensive occurrences of pseudotachylite. The pseudotachylite tends to occur as simple veins and injected networks along the NE-SW-trending fracture zones or shear zones, which are parallel to the Tanlu fault zone and cut all the pre-Cretaceous geological bodies. The characteristics of both the microstructures gained by the optical microscope and SEM imaging and the geochemistry between the pseudotachylites and their host rocks show that the pseudotachylites were formed mainly by ultracataclasis of their wall rocks in which they occur. The bulk K-Ar ages of the pseudotachylites yielded a narrow range of 81 -93 Ma, and moreover the laser-probe 40Ar/39Ar dating of phengite overprinting on the pseudotachylite gave a weighted mean age of 78.9 Ma. These results show that the pseudotachylites from the eastern Dabieshan Mountains formed along the NE-SW-trending fault zone during the uplifting of the orogenic belt at 80-90 Ma, which places important constrains on the cooling and exhumation history of the Dabieshan Mountains during and after the late Cretaceous.Recent field survey in the eastern Dabieshan Mountains has revealed extensive occurrences of pseudotachylite. The pseudotachylite tends to occur as simple veins and injected networks along the NE-SW-trending fracture zones or shear zones, which are parallel to the Tanlu fault zone and cut all the pre-Cretaceous geological bodies. The characteristics of both the microstructures gained by the optical microscope and SEM imaging and the geochemistry between the pseudotachylites and their host rocks show that the pseudotachylites were formed mainly by ultracataclasis of their wall rocks in which they occur. The bulk K-Ar ages of the pseudotachylites yielded a narrow range of 81 -93 Ma, and moreover the laser-probe 40Ar/39Ar dating of phengite overprinting on the pseudotachylite gave a weighted mean age of 78.9 Ma. These results show that the pseudotachylites from the eastern Dabieshan Mountains formed along the NE-SW-trending fault zone during the uplifting of the orogenic belt at 80-90 Ma, which places important constrains on the cooling and exhumation history of the Dabieshan Mountains during and after the late Cretaceous.

关 键 词：PSEUDOTACHYLITE ORIGIN microstructure geochemistry age the eastern Dabieshan Mountains 

分 类 号：P588.145[天文地球—岩石学] P596[天文地球—地质学]