流体作用对岩石流变行为的影响--以粤北塘洞韧性剪切带为例

Influence of fluid flow on rheological behavior of rocks:a case study of Tangdong ductile shear zone in northern Guangdong

流体的加入会较大程度地降低岩石的流变强度,产生弱化效应并使得岩石由脆性向韧性转变。发育在诸广山印支期花岗岩中的塘洞韧性剪切带为一高角度的、以压扁为主兼具右行走滑的变形带,其韧性变形具有西强东弱、南强北弱的宏观特征。详细的野外构造解析与显微构造观察表明,该剪切带横向上的不对称性和走向上的差异变形,是由以大量富硅流体贯入为标志的流体作用,通过反应弱化(长石向石英、绢云母转化)、升温效应和(或)水解弱化等机制导致。流体作用导致岩石的流变弱化可作为流体来源于同构造析出的重要证据。塘洞韧性剪切带内大量发育的面理化石英脉为韧性剪切变形同构造分泌结晶脉,其年代学分析将塘洞韧性剪切带活动时代限定在早燕山期。

The addition of fluid will greatly reduce the rheological strength of rock. The weakening effect changes the rock from brittleness to toughness. The Tangdong ductile shear zone developed in the Indosinian granites in Zhuguangshan area is a high angle deformation zone, characterized by flattening and dextral strike slip. Its ductile deformation is characterized by strong in the west and weak in the east, strong in the south and weak in the north. Detailed field structural analysis and microstructure observation show that the lateral asymmetry and strike difference of the shear zone were caused by the fluid action marked by the penetration of large amount of silicon rich fluid, which was caused by reaction weakening(transformation of feldspar to quartz and sericite), heating effect and(or) hydrolysis weakening. Furthermore, the rheological weakening of rocks by fluid interaction can be regarded as an important evidence that the fluids are derived from syntectonic precipitation. Therefore, large numbers of foliation fossil veins developed in the Tangdong ductile shear zone are syntectonic secretory crystallization veins of ductile shear deformation, and their chronological analysis indicates that the Tangdong ductile shear zone was formed in the early Yanshanian.