喜马拉雅东构造结石英EBSD组构研究及地壳构造变形环境指示

Quartz EBSD fabric in the Eastern Himalayan Syntaxis and its implications for crustal deformation environments

东构造结是喜马拉雅造山带构造变形和变质作用最强烈、岩浆作用和深熔作用最复杂的地区之一,是研究喜马拉雅地壳变形的理想场所。本文基于野外大比例尺填图,结合宏观与微观构造解析以及石英组构数据分析,得出以下结果:(1)东久-米林剪切带中段以左行走滑为主,其变形温度为300~550℃;直白-丹娘韧性拆离断层表现为上盘向NW方向运动,其变形温度为400~650℃。(2)研究区经历过高温变质至低温变形的过程,组构特征表现出从柱面<c>滑移至底面滑移的演化过程。在直白-丹娘韧性拆离断层两侧,构造变形呈不连续性,从而为进一步解体南迦巴瓦变质体和重塑区域构造演化过程提供了重要依据。

The Eastern Himalayan Syntaxis is one of the most intensely deformed and metamorphosed regions of the Himalayan Orogen,characterized by the most complex magmatic and anatectic processes.It serves as an ideal location for studying crustal deformation in the Himalayan Orogen.Based on geological mapping data,and combined with macroscopic/microscopic structural observation and quartz fabric analysis data,the following results can be withdrawn:(1)The central segment of the Dongjiu-Milin shear zone is primarily associated with sinistral shearing,whose deformation temperatures were between 300~550℃.In contrast,the Zhibai-Danniang ductile detachment fault predominantly exhibits top-to-NW shearing within the deformation temperature range of 400~650℃.(2)The study area underwent deformations from high-temperature to low-temperature,displaying a fabric evolution characterized by prism<c>slip to basalslip.Detailed quartz lattice preferred orientation(LPO)data define a structural discontinuity in the Eastern Himalayan Syntaxis region,and this discontinuity is marked by quartz LPO-defined deformation temperatures.It provides crucial tectonic evidence for the further disintegration of the Namche Barwa metamorphic complex.And the recognition of this discontinuity in the Eastern Himalayan Syntaxis is consistent with other similar structures identified along the Himalaya,which is very important for our understanding of the kinematic evolution of large orogenic belts.