中亚造山带南缘晚侏罗世陆内伸展:阿拉善北大山镁铁质岩的证据  

Late Jurassic intraplate extension in southern Central Asian Orogenic Belt:Evidence from Beidashan mafic rocks in Alxa

作　　者：王对兴 王志伟 周文辉 左晓红 陈思宇 WANG DuiXing;WANG ZhiWei;ZHOU WenHui;ZUO XiaoHong;CHEN SiYu(Hebei Key Laboratory of Strategic Critical Mineral Resources,Shijiazhuang 050031,China;Hebei Province Collaborative Innovation Center for Strategic Critical Mineral Research,College of Earth Sciences,Hebei GEO University,Shijiazhuang 050031,China;Hohhot General Survey of Natural Resources,China Geological Survey,Hohhot 010010,China)

机构地区：[1]河北省战略性关键矿产资源重点实验室,石家庄050031 [2]河北省战略性关键矿产研究协同创新中心,河北地质大学地球科学学院,石家庄050031 [3]中国地质调查局呼和浩特自然资源综合调查中心,呼和浩特010010

出　　处：《岩石学报》2023年第5期1276-1292,共17页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41802053)资助.

摘　　要：阿拉善地块北缘晚中生代(晚侏罗世-早白垩世)时期发育有广阔的伸展盆地体系,其形成可能与陆内伸展作用有关。本文首次在阿拉善地块西北缘北大山陶来地区识别出一套晚侏罗世镁铁质-超镁铁质岩,对其进行系统的岩石学、年代学和地球化学研究,从而为该地区陆内伸展提供岩浆作用方面的证据。LA-ICP-MS锆石U-Pb定年结果表明,北大山陶来地区角闪辉长岩形成时代为155.7±4.6Ma(MSWD=1.5),即晚侏罗世。角闪辉长岩显示出高铝基性岩的地化特征,如低SiO 2(48.0%~52.5%),高Al 2O 3(15.3%~18.2%)、MgO(8.78%~10.6%)和CaO(12.8%~16.7%)。此外,它们还显示出高的Mg#(72~82)、Cr(295×10^(-6)~960×10^(-6))和Ni(97.4×10^(-6)~186×10^(-6)),N-MORB型和平坦的HREE配分形式、Eu正异常,较高的Nb/La比值,这些都表明其可能为软流圈地幔减压熔融产生的原始岩浆与壳幔过渡带中含斜长石堆晶岩相互作用后分离结晶的产物。富铝和富钙源区以及岩浆中高的水含量抑制斜长石早期成核与生长共同控制了高铝角闪辉长岩的形成。辉长岩表现出N-MORB型全岩地球化学特征和板内成因岩浆锆石特征(高Nb/Hf及低Hf/Th、Th/Nb),均揭示了阿拉善西北缘陶来地区晚侏罗世镁铁质-超镁铁质岩体是板内岩石圈伸展作用的产物。在古亚洲洋最终碰撞闭合后伸展基础上,蒙古-鄂霍茨克洋闭合与古太平洋俯冲后撤叠加作用引发了岩石圈伸展,并沿中亚造山带南缘多个古生代缝合带产出了194~124Ma多期镁铁质-超镁铁质岩。A broad extensional basin system developed in the northern margin of the Alxa Block during the Late Mesozoic(Late Jurassic-Early Cretaceous),whose generation may be related to intracontinental extension.In this paper,we firstly identified a suit of Late Jurassic mafic to ultramafic rocks from Beidashan Taolai region in the northwestern margin of the Alxa Block,and systematically studied their petrology,geochronology and geochemistry to provide evidence for magmatism associated with the intracontinental extension.LA-ICP-MS zircon U-Pb dating results indicate that the Taolai hornblende gabbro was formed in 155.7±4.6Ma(MSWD=1.5),i.e.,Late Jurassic.The Taolai hornblende gabbros show the geochemical properties of high alumina mafic rocks,such as low SiO 2(48.0%~52.5%),and high Al 2O 3(15.3%~18.2%),MgO(8.78%~10.6%)and CaO(12.8%~16.7%).The high Mg#(72~82),Cr(295×10^(-6)~960×10^(-6))and Ni(97.4×10^(-6)~186×10^(-6)),N-MORB-like and flat HREE patterns,positive Eu anomalies,and high Nb/La values of the hornblende gabbros indicate that they may be the product of the fractional crystallization of the primary magma produced by decompressional partial melting of the asthenosphere mantle,which interacted with the plagioclase-bearing cumulates in the mantle-crust transition zone.The Al-and Ca-rich source and high water content in magma that inhibited the early nucleation and growth of plagioclase,controlled the formation of high-Al hornblende gabbro.The N-MORB affinity and the within-plate origin magmatic zircons with high Nb/Hf,low Hf/Th and Th/Nb reveal that the Taolai Late Jurassic mafic to ultramafic rocks in the northwestern margin of Alax Block were the products of intraplate lithosphere extension.On the basis of the extension after the final closure of the Paleo Asian Ocean,the lithosphere extension was triggered by the closure of the Mongolian-Okhotsk Ocean and the retreating subduction of the Paleo Pacific Ocean,which led to the generation of 194~124Ma multistage mafic to ultramafic rocks in the Paleozoic suture bel

关 键 词：阿拉善地块 中亚造山带 高铝基性岩 晚侏罗世 岩石圈伸展 

分 类 号：P588.124[天文地球—岩石学] P597.3[天文地球—地质学]