Superposition of Paleo-Asian and West-Pacific Tectonic Domains in the Eastern Section of the Solonker Suture Zone:Insights from Petrology,Geochemistry and Geochronology of Deformed Diorite in Xar Moron Fault Zone,Inner Mongolia
Superposition of Paleo-Asian and West-Pacific Tectonic Domains in the Eastern Section of the Solonker Suture Zone:Insights from Petrology,Geochemistry and Geochronology of Deformed Diorite in Xar Moron Fault Zone,Inner Mongolia
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2012
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通讯作者：
Li Fu-lin
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作者：
Li Fu-lin
内蒙古林西县西拉木伦断裂带发育一些闪长岩群，侵入双井片岩中，并表现出不同程度的变形。本文对闪长岩进行了岩石学、地球化学、LA-ICPMS U-Pb锆石年龄和角闪石40Ar-39Ar年龄的研究。LA-ICPMS U-Pb表明该闪长岩侵位于早二叠世。锆石年龄为286±1 Ma。岩浆来源于板片衍生流体或熔体交代的富集地幔。早侏罗世闪长岩经历了绿帘-角闪岩相变质作用，角闪石40Ar-39Ar年龄为188.7±1.4 Ma。研究表明，索伦克缝合带早古生代和较年轻的基性岩来源于俯冲沉积物交代的地幔，且交代作用随着时间的推移而增强。晚石炭世（~310 Ma）之前发生了一个碰撞阶段，索伦克缝合带在晚石炭世至早二叠世（~310~276 Ma）经历了造山后伸展。所研究的闪长岩是闪长岩的一部分。在缝合带的这一伸展时期形成的广泛的闪长岩-花岗闪长岩套。在晚二叠世大洋盆地中，局部发生在缝合带中。这些盆地的闭合导致了晚二叠世至中三叠世（约272至230 Ma）期间索伦克缝合带的最终碰撞。最终碰撞时间的空间变化导致了缝合带中同碰撞和后碰撞花岗岩的同时形成索伦克缝合带的闭合导致华北克拉通与其北部的一些微大陆合并。在增生的微大陆以北，古太平洋的分支蒙古鄂霍次克洋在北边的西伯利亚克拉通和南边的华北克拉通之间形成了剩余的北东向洋域。蒙古鄂霍次克洋在东北部的闭合早侏罗世蒙古引发索伦闪长岩角闪石40Ar-39Ar年龄记录的陆陆碰撞，研究区随后进入造山后伸展，而更东的古太平洋板块俯冲到华北克拉通之下。区域后造山伸展与远距离俯冲的结合导致了现在中国东北地区侏罗纪的交替挤压和伸展。晚侏罗世古太平洋板块，中国东北地区的构造环境最终变为拉张，进入西太平洋构造域。
Some diorite stocks developed in the Xar Moron fault belt in Linxi county,Inner Mongolia.They intruded into the Shuangjing schist and display variable degrees of deformation.This study presents the petrology,geochemistry,a LA-ICPMS U-Pb zircon age and a hornblende 40Ar-39Ar age of the diorite.The diorite was emplaced in the Early Permian,as reflected by a LA-ICPMS U-Pb zircon age of 286±1 Ma.The magma is derived from enriched mantle metasomatized by slab-derived fluids or melts.The diorites were subject to epidote-amphibolite facies metamorphism during the Early Jurassic,resulting in a hornblende 40Ar-39Ar age of 188.7±1.4 Ma.Combining the new data with the latest published results from the study area and the region,we conclude that the Early Paleozoic and younger mafic rocks in the Solonker suture zone are derived from mantle that was metasomatized by subducted sediments,and that metasomatism increased with time.A stage of collision occurred before the Late Carboniferous(~310 Ma) and the Solonker suture zone underwent post-orogenic extension during the Late Carboniferous to Early Permian(~310 to 276 Ma).The diorite studied is part of a widespread diorite-granodiorite suite that formed during this period of extension in the suture zone.In the Late Permian oceanic basins occurred locally in the suture zone.The closure of these basins induced the final collision of the Solonker suture during the Late Permian to Middle Triassic(~272 to 230 Ma).Spatial variation in the timing of final collision led to the coeval formation of syn-collisional and post-collisional granites in the suture zone.Closure of the Solonker suture zone resulted in the amalgamation of the North China Craton with some microcontinents to its north.North of the accreted microcontinents,the Mongol-Okhotsk Ocean,a branch of the Paleo-Pacific Ocean,formed the remaining NE-striking oceanic domain between the Siberia Craton to the north and the North China Craton to the south.The closure of the Mongol-Okhotsk Ocean in NE Mongolia in the Early Jurassic induced the continent-continent collision recorded by the hornblende 40Ar-39Ar age from the Solonker diorite.The research area then entered post-orogenic extension,while further east the Paleo-Pacific plate subducted beneath the North China Craton.The combination of regional post-orogenic extension and distant subduction led to alternating compression and extension in the Jurassic in what is now northeastern China.After the change in the subduction direction of the Paleo-Pacific plate in the Late Jurassic,the tectonic environment in northeastern China finally became extensional and the region entered the West-Pacific tectonic domain.