中下地壳切向分层流变的结果:喜马拉雅东段雅拉香波片麻岩穹隆  

The result of tangential layered solid-state flow deformation in the middle and lower crust:The Yardoi dome in the eastern Himalayan orogenic belt

作　　者：江成宇 周保军 陈小宇[1,2] 刘俊来 JIANG ChengYu;ZHOU BaoJun;CHEN XiaoYu;LIU JunLai(State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences(Beijing),Beijing 100083,China;Frontiers Science Center for Deep-time Digital Earth,China University of Geosciences(Beijing),Beijing 100083,China)

机构地区：[1]中国地质大学(北京)地质过程与矿产资源国家重点实验室,北京100083 [2]中国地质大学(北京)深时数字地球前沿科学中心,北京100083

出　　处：《岩石学报》2024年第5期1628-1646,共19页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(42172246);深时数字地球前沿科学中心项目(2652023001)联合资助.

摘　　要：大陆中、下地壳切向(近水平)分层固态流动变形是地壳物质流动的重要形式之一,也是片麻岩穹隆的重要形成机制。雅拉香波穹隆位于特提斯喜马拉雅构造带的最东段,出露不同变质级别和时代的岩石地层,发育强烈的韧性剪切变形以及多期岩浆事件,是研究造山过程中构造变形和岩浆历史的天然实验室。本文以该穹隆为研究对象,进行了详细的野外构造解析和显微观察等工作,总结出以下三个特点:(1)雅拉香波穹隆内不同构造层次的岩石经历了相同的构造体制和不同变形条件改造:从浅部到深部,变形温度逐渐递增,由390℃到600℃;差应力逐渐减小,从24.58MPa减少至8.72MPa;应变速率逐渐加快,从1.27×10^(-13)~1.28×10^(-13)/s增加到5.19×10^(-11)~5.21×10^(-11)/s。以上体现了地壳活动带强烈的分层流变特点。(2)结合前人研究划分了穹隆变形的三个期次(D_(1)、D_(2)和D_(3)),其中D_(1)表现为上盘向南的剪切方向,D_(2)则表现为上盘向北的剪切方向。进一步,将主要变形期次D_(2)进一步划分为两个阶段,早期主要是以单剪为主导的剪切作用类型,而晚期则是以纯剪为主导的剪切作用类型。(3)根据D_(2)面理和线理的产状分布特点,可以得出,深部岩石线理的倾伏角近水平,而浅层次岩石的线理倾伏角近竖直。基于以上研究表明,雅拉香波穹隆各部分岩石均遭受了不同程度的剪切改造,不同构造层次的岩石具有几何学上的一致性以及运动学上的解耦,体现了穹隆发育过程中运动方向上的转变。结合穹隆各部位线理的倾伏角的变化规律,本文认为雅拉香波穹隆记录了中下地壳分层流动的过程,穹隆的形成主要受中下地壳近水平切向流动控制,辅以垂向流动的改造。Tangential(near-horizontal)layered solid-state flow deformation in the middle and lower crust of the continent is one of the important forms of crustal material flow,and it is also an important formation mechanism of gneiss domes.The Yardoi Dome,located in the eastern end of the Tethyan Himalayan sequence,consists of a series of rocks of different ages and metamorphic grades that resulted from a series of intensely ductile shear deformations and multiple magmatic events.It is a natural laboratory for the study of tectonic deformation and magmatic history during the orogenic process.This study takes the Yardoi dome as the research object,and carries out detailed field tectonic analysis and microscopic observation,etc.,from which the following three characteristics are summarized:(1)The rocks at different crust levels within the Yardoi dome have experienced the same tectonic mechanism but with different deformation conditions:the deformation temperature gradually increases from 390℃to 600℃from the up to the lower units of the dome;the differential stress gradually decreases from 24.58MPa to 8.72MPa;the strain rate gradually accelerates from 1.27×10^(-13)~1.28×10^(-13)/s to 5.19×10^(-11)~5.21×10^(-11)/s,reflecting the strong stratified rheological characteristics of the active crustal zone.(2)Three stages of the dome deformation(D _(1),D_(2) and D 3)are confined in conjunction with the previous studies.The D_(1) is a top-to-S shear,and the D_(2) is a top-to-N shear.The main deformation phase D_(2) is further divided into two phases,i.e.,the early phase and the main deformation phase D_(2).The D_(2) is further divided into two phases,among which the early phase is mainly the type of shear dominated by single shear,while the late phase is the type of shear dominated by pure shear.(3)With regard to the distribution characteristics of the foliations and lineations in the D_(2),it can be concluded that the plunge of the lineations of the deeper rocks is nearly horizontal,whereas that of the shallower rocks is nea

关 键 词：藏南 雅拉香波片麻岩穹隆 穹隆形成机制 中下地壳 分层固态流变 应变速率 运动学涡度 

分 类 号：P542[天文地球—构造地质学] P597.3[天文地球—地质学]