| 古亚洲构造域和西太平洋构造域在索伦缝合带东段的叠加: 来自内蒙古林西县西拉木伦断裂带内变形闪长岩的岩石学、地球化学和年代学证据 |
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| 引用本文： | 李益龙,周汉文,肖文交,钟增球,尹淑苹,李福林.古亚洲构造域和西太平洋构造域在索伦缝合带东段的叠加: 来自内蒙古林西县西拉木伦断裂带内变形闪长岩的岩石学、地球化学和年代学证据[J].地球科学,2012,37(3):433-450. |
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| 作者姓名： | 李益龙 周汉文 肖文交 钟增球 尹淑苹 李福林 |
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| 作者单位： | 1.中国地质大学地球科学学院, 湖北武汉 430074 |
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| 基金项目： | 国家"973"项目2007CB411307国家自然科学基金项目40725009中国地质调查局项目1212010510507 |
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| 摘 要： | 在内蒙古林西县西拉木伦断裂带内发育岩株状产出并具有不同程度变形特征的闪长岩体, 岩体侵入到双井片岩中.对该闪长岩进行了岩石学、地球化学、锆石LA-ICPMS U-Pb年龄和角闪石40Ar-39Ar年龄的研究.结果表明内蒙古林西县西拉木伦断裂带内的变形闪长岩侵位于早二叠世, 其锆石LA-ICPMS U-Pb年龄为286±1 Ma.岩浆来源于俯冲带流体/熔体交代作用而形成的富集地幔.岩石遭受了早侏罗世绿帘角闪岩相变质作用, 角闪石40Ar-39Ar年龄为188.7±1.4 Ma.结合研究区及邻区近年来的新成果认为索伦缝合带早古生代以来的镁铁质岩石均显示来源于相对富集LILE、LREE的地幔, 与俯冲流体或熔体的改造作用相关, 并且随着时代的更新改造程度显示增强的趋势.索伦缝合带在晚石炭世(~310 Ma)之前发生过闭合碰撞, 晚石炭世-早二叠世(~310~276 Ma)处于后造山伸展的背景, 在伸展环境下形成了华北北缘该时期广泛分布的闪长岩-花岗闪长岩带, 报道的闪长岩即为该时期的产物.晚二叠世缝合带局部区域存在洋盆, 洋盆的闭合导致了晚二叠世-中三叠世(~272~230 Ma)索伦缝合带的最终碰撞缝合, 最终碰撞缝合在空间上的不均一性形成了缝合带内该时期大量并存的同碰撞花岗岩和后碰撞花岗岩.索伦缝合带的缝合导致华北板块与其北部各微陆块的拼合, 此时蒙古-鄂霍次克海作为古太平洋的一个分支北东向展布于西伯利亚板块和拼合后的华北板块之间.早侏罗世蒙古-鄂霍次克海在蒙古东北部发生闭合, 本文报道的角闪石40Ar-39Ar年龄记录了洋壳闭合后陆-陆碰撞的变质时间, 之后研究区进入后造山伸展的环境.此时在古太平洋板块向华北板块俯冲应力的共同作用下, 华北东部在侏罗纪出现挤压机制与拉张机制的多次转换.晚侏罗世古太平洋板块俯冲方向转变后, 中国东部进入持续的拉张背景, 并转入西太平洋构造域的范畴.
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| 关 键 词： | 古亚洲构造域 太平洋构造域 索伦缝合带 西拉木伦断裂带 岩石学 地球化学 内蒙古 |
| 收稿时间： | 2011-09-23 |
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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| Abstract: | 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. |
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