印度-欧亚板块碰撞带中下地壳分层流动与减薄:来自希夏邦马峰地区藏南拆离系构造解析的证据
Middle to lower crustal stratified flow and thinning within the Indian-Eurasian collision zone:Evidence from structural analysis of the South Tibetan Detachment System in the Shisha Pangma region
闫佳鑫 1刘俊来 2周保军 3闻俊豪4
作者信息
- 1. 中国地质调查局西安地质调查中心(西北地质科技创新中心),中国地质调查局造山带研究中心,西安 710119;中国地质大学地质过程与矿产资源国家重点实验室,北京 100083
- 2. 中国地质大学地质过程与矿产资源国家重点实验室,北京 100083;中国地质大学(北京)深时数字地球前沿科学中心,北京 100083
- 3. 中国地质大学地质过程与矿产资源国家重点实验室,北京 100083
- 4. 中国前寒武系省级地质自然保护区管护局,昆明 650600
- 折叠
摘要
造山带中下地壳物质流动是造山带地壳变形的重要表现,它制约着造山作用过程.印度-欧亚板块碰撞带内藏南拆离系为理解陆-陆板块会聚过程中中下地壳物质流动提供了范例.本项研究围绕喜马拉雅造山带中段希夏邦马峰地区藏南拆离系开展构造解析、显微构造观察和淡色花岗岩独居石U-Th-Pb年代学分析.结果表明希夏邦马峰地区藏南拆离系为一宽约2km的韧性剪切带,剪切变形岩石具有显著的分层流动特征.藏南拆离系新生代时期经历了两阶段塑性变形:D1期变形表现为面理S1、对称状透镜体和层间褶皱F,的发育;D2期变形表现为糜棱面理S2、近E-W向拉伸线理L2、不对称旋转碎斑和透镜体及褶皱的发育.运动学标志表明D2期变形为上盘向东的运动学特征.淡色花岗岩独居石U-Th-Pb测年分析获得三组年龄:32.26±0.29Ma、22.31±0.18Ma和15.54±0.11Ma,这三组年龄的淡色花岗岩分别表现出D,期变形、D2期变形和未变形特征.结合前人已发表数据,本文得出藏南拆离系ca.35～26Ma发生以纯剪为主的剪切变形(D1期),ca.26～15Ma发生以单剪为主的剪切变形(D2期).D1-D2期变形为一递进剪切变形,二者可能归咎于印度-欧亚板块碰撞过程中中下地壳固态分层流动.
Abstract
Middle to lower crustal flow is an important manifestation of crustal deformation in orogenic belts,which controls the dynamic evolution process of the orogeny.The South Tibetan Detachment System(STDS)within the Indian-Eurasian collision zone provides valuable insights into the middle to lower crustal flow during the continental convergence.In this contribution,integrated structural and microstructural analyses,and LA-ICP-MS U-Th-Pb dating of monazite from leucogranites within the STDS in the Shisha Pangma region in the middle part of the Himalayan orogen are conducted.The results reveal that the STDS in the Shisha Pangma region represents a ductile shear zone with a width of ca.2 km,in which the constituent rocks are characterized by remarkable layered rock rheology.At the meantime,the Cenozoic evolution of the STDS in the region is divided into two stages:D,structures,characterized by development of foliation S1,symmetrical lenses and intrafolial folds(F1);D2 structures,characterized by development of mylonitic foliation(S2),near E-W stretching lineation(L2),asymmetrical rotational porphyroclasts,lenses and folds.Kinematic indicators within the STDS are compatible with top-to-east shearing during D2 deformation.Monazite U-Th-Pb dating on three leucogranites yielded ages of 32.26±0.29Ma,22.31±0.18Ma and 15.54±0.11 Ma,which exhibit characteristics corresponding to D1,D2 and post-deformation of leucogranites,respectively.Combined with published data,it is concluded that the STDS experienced pure shear-dominated shearing(D1)at ca.35～26Ma,followed by simple shear-dominated shearing(D2)at ca.26～15Ma.The D1-D2 deformation is characterized by a successive process,possibly attributed to middle to lower crustal stratified flow during the Indian plate and Eurasian plate collision.
关键词
构造解析/独居石U-Th-Pb测年/希夏邦马峰地区/藏南拆离系/中下地壳分层流动Key words
Structural analysis/Monazite U-Th-Pb dating/Shisha Pangma region/South Tibetan Detachment System/Middle to lower crustal stratified flow引用本文复制引用
基金项目
国家自然科学基金(4217226)
中央高校基本科研业务费专项深时数字地球中央高校科技领军人才团队项目(2652023001)
陕西省自然科学基金(2024JC-YBQN-0249)
出版年
2024
NETL
NSTL
维普
万方数据