摘要
发育在大别造山带东部的假玄武玻璃是区域内 NE— SW向断裂带快速滑移形成的构造岩。地质产状、显微构造及岩石化学研究表明 ,这些假玄武玻璃主要由超碎裂岩化作用所形成。假玄武玻璃及围岩的全岩(包括部分单矿物 ) K- Ar年龄测定表明 ,大别造山带的假玄武玻璃形成于 81～ 93Ma之间。本文同时测定了叠加在假玄武玻璃基质之上的多硅白云母的激光 4 0 Ar/39Ar年龄为 78.9Ma。显微构造及所获得的年龄数据显示 ,这些沿NE— SW向断裂发育的假玄武玻璃是在晚白垩世 (80～ 90 Ma)时期伴随着大别造山带整体隆升过程形成的 ,而与早期板块俯冲过程无关。同时 ,不同定年方法在数据上的一致性还表明 ,全岩 K- Ar方法在确定某些假玄武玻璃及含假玄武玻璃的断裂构造年代时 。
Pseudotachylites developed along the NE-SW trending faults in the eastern Dabie Mountains are a tectonite formed by ultracataclasis of rapid faulting, which is testified by the characteristics of its occurrence and microstructure, as well as lithochemistry. The bulk K-Ar ages of the pseudotachylites and their respective wall rocks from different localities yielded a narrow range of 81～93 Ma, and moreover, the laser probe 40Ar/ 39Ar dating of phengite overprinting the pseudotachylite gave a weighted mean age of 78.9 Ma. These results show that the pseudotachylites from the eastern Dabie Mountains formed along the NE-SW-trending fault zone during the uplifting of the orogenic belt at 80～90 Ma, which places important constraints on the cooling and exhumation history of the Dabie Mountains during and after the Late Cretaceous. Furthermore, the correspondence of the ages obtained from the above two different methods suggests that the bulk K-Ar dating technique is still an effective method to determine the age of some crushing-generated pseudotachylites and therefore the age of the pseudotachylite-bearing faults, especially for younger tectonic events.
出处
《地质学报》
EI
CAS
CSCD
北大核心
2004年第3期374-379,i002,共7页
Acta Geologica Sinica
基金
国家自然科学基金项目 (编号 40 172 0 77)
国土资源大调查项目 (编号 2 0 0 0 13 0 0 0 169)资助成果
