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茫崖二长花岗岩锆石U-Pb 年代学、Lu-Hf 同位素特征及岩石成因
Petrogenesis, Zircon U-Pb Chronology, and Lu-Hf Isotopic Characteristics of Monzonitic Granite from Mangya Area

DOI: 10.3799/dqkx.2018.326

Keywords: 南阿尔金南缘,二长花岗岩,LA-ICP-MS,I型花岗岩,分离结晶,岩石学.
south margin of South Altun
, monzonitic granite, LA-ICP-MS, I-type granite, fractionation, petrology.

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Abstract:

阿克腾龙山二长花岗岩位于南阿尔金茫崖地区北侧,讨论其成因类型、成岩年代以及构造环境,进而探讨南阿尔金造山带早古生代岩浆活动及壳幔相互关系.利用岩石地球化学、LA-ICP-MS锆石U-Pb年代学和Lu-Hf同位素分析研究了岩体的成因类型、成岩时代、物质来源和成岩环境.研究表明,该岩体属于弱过铝质、高钾钙碱性I型花岗岩.富集轻稀土元素,而相对亏损重稀土元素;岩浆演化过程中可能发生了以角闪石、磷灰石和金红石为主的分离结晶.岩体的成岩年龄为435~449 Ma.锆石的 ε Hf( t )正、负值各半,说明岩体可能来源于古老地壳和新生地壳的混合物质,可能是新生地壳部分熔融并混合部分古老地壳物质形成,或者是新生地壳和古老地壳的混合物质部分熔融,经历分离结晶而成.成岩环境可能是俯冲洋壳板片断离后,由碰撞挤压转向伸展抬升的构造环境.
Aketenglongshan monzonitic granite is located in the south margin of South Altyn. Here we present whole-rock geochemistry, zircon U-Pb geochronology and Hf isotope analysis to study the petrogenesis and magmatic evolution of the granite, which belong to high-K calc-alkaline, weakly peraluminous series and I-type granite. The geochemical characteristics show strongly fractionation of the REEs, and enrichment in LREE, while depletion in HREE. It is infered that amphibole, apatite and rutile fractionation occurred during the magmatic evolution. The zircon U-Pb age of the granite is 435–449 Ma, representing the crystallization age of the granite. The half negative and half positive value of zircon ε Hf( t ) indicates that the origin of the monzonitic granite is mixture of juvenile and ancient crust materials, and the granites were derived from the partially melted juvenile crust, and mixed with ancient crust materials during the upwelling, or derived from the partially melted mixture of juvenile and ancient crust materials, in extensional environment transformed from compressional environment after the break off of the subducted oceanic crust

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