中亚造山带东部西拉木伦构造带深部地球动力学过程初探  

A Preliminary study on deep geodynamic process of Xar Moron tectonic belt in eastern Central Asia Orogenic Belt

作　　者：宋时雨 田博雅 李庆洋 徐备 SONG ShiYu;TIAN BoYa;LI QingYang;XU Bei(Hebei Key Laboratory of Strategic Critical Mineral Resources,Hebei GEO University,Shijiazhuang 050031,China;College of Earth Sciences,Hebei GEO University,Shijiazhuang 050031,China;The Seventh Geological and Mineral Exploration Institute of Shandong Province,Linyi 276006,China)

机构地区：[1]河北地质大学河北省战略性关键矿产资源重点实验室,石家庄050031 [2]河北地质大学地球科学学院,石家庄050031 [3]山东省地质矿产勘查开发局第七地质大队,临沂276006

出　　处：《岩石学报》2023年第5期1293-1304,共12页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(42172248、42042029);中国地质调查局项目(DD20190004)联合资助.

摘　　要：板块汇聚边缘的陆壳厚度变化与构造和岩浆过程的动态相互作用有着错综复杂的联系,也是对深部地球动力学背景的直接响应。西拉木伦构造带是中亚造山带东部重要的汇聚板块边界,查明其浅部构造变形及深部动力学过程对于理解中亚造山带构造演化具有重要意义。本文通过野外地质工作查明晚二叠世-早三叠世西拉木伦构造带的上地壳发育一系列北东向、轴面向南东倾的宽缓褶皱以及向南东逆冲的断层,变形样式属于薄皮构造,显示出由北西向南东挤压的单向构造应力背景,平衡剖面恢复显示此时期构造变形造成地表~30%的缩短以及~4km的浅部地壳增厚。利用林西地区火成岩全岩La/Yb比值和锆石Eu/Eu*参数构建的年龄-地壳厚度曲线揭示,二叠纪早-中期地壳厚度从49km连续减薄到33km,反映此时期整体处于伸展环境。二叠纪晚期至三叠纪初期,地壳厚度增加了~15km,峰值厚度达~48km,这个迅速的地壳增厚过程可能是岩浆作用导致的地壳垂向增生和构造作用产生的造山带物质堆叠综合作用的结果。本文根据构造带同汇聚期岩浆岩面积和地壳厚度估算造山作用形成了~11%的新生陆壳。同时,两个时期的深部壳幔相互作用方式也有不同,二叠纪早期西拉木伦构造带火成岩锆石的εHf(t)值相对较高(6.1~19.9;均值10.1),δ^(18 )O值较分散(5.1‰~8.3‰),指示岩浆在形成过程中有幔源物质的加入,示踪了林西地区深部与软流圈上涌有关的伸展过程;而晚二叠世至三叠纪初期花岗岩锆石εHf(t)值相对下降(-1.1~17.2;均值9.3),δ^(18 )O值仍高于幔源值(>5.9‰),揭示同源地幔岩浆的持续重融改造过程。综合沉积环境、地壳厚度变化、岩浆岩同位素变化、地壳增生量及地表单向构造应力背景等特征,本文提出西拉木伦构造带可能经历了地幔俯冲;而早-中二叠世的软流圈上涌和晚二叠世-早三叠世的下The thickness variation of the continental crust at the convergent margin is intricately linked to the dynamic interaction between tectonic and magmatic processes and is also a direct response to the deep Earth dynamics.The Xar Moron tectonic belt underwent a major tectonic transformation from extension to compression during the Early Triassic,and studies on its deep dynamic process is of significance for understanding the tectonic evolution of the Central Asian Orogenic Belt.In this study,through detailed field geological survey,a series of wide and gentle northeast-trending folds and south-dipping thrust faults were found in the upper crust of the Xar Moron tectonic belt,with deformation patterns characteristic of thin-skinned structures,which shows a unidirectional shortening from northwest to southeast.Balance cross-section restorations suggest that the structural deformation caused~30%of shortening and~4km of upper crustal thickening.A crustal thickness-age curve has been constructed using published geochemical data of Permian to Triassic magmatic and sedimentary rocks in the Linxi area.The data suggests that during the Early to Middle Permian,the crustal thickness was continuously thinned from 49km to 33km,indicating an overall extension period.In the Late Permian to Early Triassic,the crustal thickness was increased by~15km,and reached a peak thickness of~48km.This rapid crustal thickening process may be related to vertical crustal accretion caused by magmatic activities and mountain-building material stacking related to tectonic activitives.Based on the estimated area of magmatic rocks during the convergent period and the thickness of the crust,it is believed that the newly-formed juvenile crust account for~11%of the total crust.The interaction between the deep crust and mantle differed between these two periods.During the Early Permian in the Xar Moron tectonic belt,theεHf(t)of igneous zircons was relatively high(6.1~19.9;averaged at 10.1),with scatteredδ^(18 )O values(5.1‰~8.3‰).This indicates the

关 键 词：地幔俯冲 西拉木伦构造带 陆壳厚度 三叠纪 地球动力学 中亚造山带 

分 类 号：P542[天文地球—构造地质学]