断层泥自生伊利石年龄分析及其在龙门山断裂带的应用

韧性剪切带的活动年龄及其相关的隆升/剥蚀速率可以通过各种同位素技术进行直接测定和计算。相比较而言,由于形成于浅部低温环境,老的碎屑物质和新的重结晶物质相互掺杂,脆性断裂的同位素年龄往往代表的是一个混合年龄,难以反映其真实的活动时间。近些年来,断层泥自生伊利石定年方法在地表脆性断裂的年代学研究中展现出了良好的应用前景。文中介绍了断层泥中自生伊利石的生成过程、形貌特征和定年原理,并简要介绍了样品的处理过程和伊利石多型相对含量的确定方法。近几年,这种方法逐渐被应用于龙门山断裂带及其山前飞来峰活动时代的确定,为青藏高原东缘早期的构造活动提供了直接的年代证据。

Authigenic Illite Age Analysis for Fault Gouge and Its Application to the Longmen Shan Fault Belt

The ductile shear zone and the uplift/exhumation rate can be dated or calculated directly through various isotopic dating methods. In contrast, because the shallow crustal faulting occurs in the low-temperature brittle regime and the new growing mineral phases are mixed with old mineral phases, the result of brittle fault dating represents a mixed age instead of the true faulting time. In recent years, authigenic illite age analysis for fault gouge has a promising application in dating of brittle faults. This paper introduces the formation mechanism of authigenic illite, its morphologic characters, and dating principle. In addition, sample preparation and illite polytype quantification methods are also introduced briefly in this paper. There is a good application of this method in fault dating for the Longmen Shan fault belt and its front klippen, which provides a direct timing constraint on the early tectonic activities on the eastern margin of the Tibetan Plateau.