L构造岩成因及其岩石流变学意义  

The genesis of L-tectonics and its rheological significance

作　　者：向必伟 张子康 许德如 袁琪 熊言洁 袁方 Xiang Biwei;Zhang Zikang;Xu Deru;Yuan Qi;Xiong Yanjie;Yuan Fang(School of Earth Sciences,East China University of Technology,Nanchang 330100;Zhejiang Zhezhong Geological Engineering Survey Institute Co.,Ltd.,Jinhua,Zhejiang 321000;Geological Institute of No.9 Oil Production Plant,PetroChina Changqing Oilfield Company,Yinchuan 750005)

机构地区：[1]东华理工大学地球科学学院,南昌330100 [2]浙江省浙中地质工程勘察院有限公司,浙江金华321000 [3]中国石油长庆油田分公司第九采油厂地质研究所,银川750005

出　　处：《地质科学》2024年第6期1562-1574,共13页Chinese Journal of Geology(Scientia Geologica Sinica)

基　　金：国家自然科学基金项目“北大别造山后伸展岩石圈深部活动与动力学值模拟研究”(编号:42162019)资助。

摘　　要：L构造岩是指线理极为发育而面理发育微弱的韧性变形岩石,其被普遍认为是岩石收缩变形的结果。有限应变分析中,收缩应变表述的是两个主应变缩短的应变形式。其中,两个缩短应变量相等是发育L构造岩的理想应变形式,而两个缩短应变大小不等时变形岩石仍然能够定义面理。这就意味着笼统地使用“收缩应变”解释L构造岩的应变条件很可能存在以偏概全的风险。此外,前人从有限应变的角度分析,认为剪应变对面理与线理发育的作用有限,但对剪应变影响矿物定向从而影响组构发育还缺乏足够的认识。本次工作梳理了L构造岩分布方式和产出类型,并分析了各类L构造岩的应变特征。通过分析L构造岩在自然界中动力学边界条件,结合对大别造山带早白垩世造山后伸展活动中发育的殷店—马垄剪切带L构造岩的实际观察和分析,提出重力垮塌作用下,因中-下地壳物质垂直造山带走向流变受阻,在造山带边缘形成平行造山带走向的收缩应变带,进而发育剪切带L构造岩的构造模式。另外,根据剪应变易于集中于变形带中低流变强度区域,而形成近似完全的简单剪切变形的已有结论,提出一般剪切变形的韧性剪切带中局部低能干区域很可能发育为局部L构造岩剪切带。本文旨在通过对L构造岩成因及其动力学边界条件的综述,为实际观察和分析L构造岩提供指导。L-tectonites are characterized by well-developed lineations but weak foliations in deformed rocks,commonly associated with constrictional deformation.Constrictional strain is defined by the shortening of two of the principal strain axes.Ideally,L-tectonites form when these two shortening strains are nearly equal in magnitude.In contrast,if there is a significant disparity in the magnitudes of these principal shortening strains,foliations may develop even in the presence of two principal shortening strains.Consequently,employing“constrictional strain”as a generalized explanation for L-tectonite deformation may risk oversimplification.Furthermore,analyses from the finite strain perspective have suggested that the influence of shear strain on the formation of foliation and lineation is relatively limited.However,the impact of shear strain on mineral orientation and its subsequent inhibition of foliation development remains inadequately understood.This study aims to explore alternative models for the development of L-tectonites by reviewing their distribution patterns,analyzing the strain characteristics of various L-tectonite types,and investigating potential dynamic boundary conditions.The findings are intended to offer insights into the practical observation and analysis of the kinematic and dynamic implications of L-tectonites in regional tectonic contexts by examining their genesis and dynamic boundary conditions.

关 键 词：L构造岩 收缩应变 重力垮塌 伸展拆离 构造挤压 

分 类 号：P542[天文地球—构造地质学]