西藏冈底斯中北部永珠地区花岗岩类年代学与地球化学

发布时间：2018-04-16 11:28

本文选题：冈底斯 + 永珠地区　；参考：《吉林大学》2015年硕士论文

【摘要】：冈底斯地块中北部出露大面积中生代岩浆岩，其岩石成因与地球动力学意义一直存在争议。本文以冈底斯中北部永珠地区花岗岩类为研究对象，对其进行详细的岩石学、地球化学和锆石U-Pb年代学研究，试图为解决这问题提供资料。根据岩石野外地质特征和锆石U-Pb定年，永珠花岗岩类可以分为三期：早侏罗世（176.4Ma）、早白垩世（120~110Ma）和晚白垩世（~75Ma）。早侏罗世花岗岩岩石类型为花岗闪长岩，具弱片麻状；全岩地球化学特征显示过铝质、钙碱性特征；轻稀土富集、重稀土亏损，具明显负Eu异常；富集大离子亲石元素，亏损高场强元素。早白垩世花岗岩岩石类型为花岗闪长岩、似斑状二长花岗岩，含有暗色包体，与碳酸岩围岩接触处发生矽卡岩化、大理岩化；花岗岩与包体显示出准铝质、钙碱性-高钾钙碱性特征；轻稀土富集、重稀土亏损；富集大离子亲石元素，亏损高场强元素。晚白垩世花岗岩岩石类型为二长花岗岩、似斑状二长花岗岩，含有暗色包体，与碳酸岩围岩接触处发生矽卡岩化；花岗岩与包体显示出准铝质、钙碱性-高钾钙碱性特征；轻稀土富集、重稀土亏损；富集大离子亲石元素，亏损高场强元素。早侏罗世花岗岩为未分异S型花岗岩，早、晚白垩世花岗岩为未分异I型花岗岩；三期花岗岩均具有较高的锆石饱和温度、Mg#、Cr和Ni数值，反映形成与幔源岩浆有密切关系，其中早、晚白垩世花岗岩形成可能与岩浆混合有关；早侏罗世花岗岩岩浆源区可能为中、上地壳（变）沉积岩，早、晚白垩世花岗岩岩浆源区可能为中、上地壳角闪岩相变质基性火成岩。永珠早侏罗世过铝质、未分异S型花岗岩可能形成于班公湖-怒江和雅鲁藏布江特提斯洋双向俯冲作用影响下，中冈底斯内部发生挤压、碰撞（幔源岩浆影响?），中、上地壳（变）沉积岩熔融形成；早白垩世未分异I型花岗岩可能形成于班公湖-怒江特提斯洋南向俯冲的背景下，俯冲板片断离引起软流圈物质上涌，导致岩石圈地幔和中、上地壳发生熔融，产生基性和酸性岩性岩浆，两者发生岩浆混合作用形成；晚白垩世未分异I型花岗岩可能形成于冈底斯-羌塘地块发生碰撞进入后碰撞构造环境背景下，增厚岩石圈地幔局部发生拆沉，引起软流圈物质上涌，产生底侵幔源岩浆、促使中、上地壳熔融产生酸性岩浆，，两者发生岩浆混合作用形成。中生代冈底斯中北部动力学背景主要表现为班公湖-怒江特提斯洋的俯冲消减、冈底斯与羌塘地块碰撞以及造山后的垮塌。永珠地区与成矿作用有关的花岗岩为早白垩世和晚白垩世两期，成矿作用类型主要为矽卡岩型（铜）成矿作用。
[Abstract]:A large area of Mesozoic magmatic rocks emerged from the central and northern parts of the Gangdis block, and its petrogenesis and geodynamic significance have always been controversial.In this paper, granitic species in Yongzhu area, central and northern Gangdis, are studied in detail in petrology, geochemistry and zircon U-Pb chronology, in order to provide data for solving this problem.According to the field geological characteristics of rocks and zircon U-Pb dating, the Yongzhu granites can be divided into three stages: early Jurassic (176.4 Mai), early Cretaceous (120,110 Ma) and late Cretaceous (75 Ma).The early Jurassic granitic rocks are granodiorite with weak granodiorite, the geochemical characteristics of the whole rock show the characteristics of peraluminous, calc-alkaline, LREE enrichment, heavy REE depletion, obvious negative EU anomaly, enrichment of large ion lithophile elements,Loss of high field strength elements.The early Cretaceous granitic rocks are granodiorite, porphyry monzonitic granites, containing dark inclusion, skarn and marble in contact with the surrounding rock of carbonatite, granites and inclusions showing quasi-aluminite,The characteristics of calcium alkalinity and high potassium calcium alkalinity; light rare earth enrichment, heavy rare earth deficiency; enrichment of large ion lithophile elements, depletion of high field strength elements.The late Cretaceous granite rock type is monzogranite, similar to porphyry monzogranite, contains dark color inclusion, occurs skarn in contact with the surrounding rock of carbonatite, the granite and enclave show quasi-aluminite, calc-high-potassium calc-alkaline characteristic, granitoids and xenoliths show the characteristics of quasi-aluminite, calc-alkaline and high-potassium calc-alkaline.Light rare earth enrichment, heavy rare earth deficiency, enrichment of large ion lithophile elements, depletion of high field strength elements.The early Jurassic granites are undifferentiated S-type granites, and the early and late Cretaceous granites are undifferentiated I-type granites, and the third stage granites have higher zircon saturation temperatures, Mg#cr and Ni values, indicating that the formation of the granites is closely related to the mantle magma.The early and late Cretaceous granitic formation may be related to magmatic mixing, the early Jurassic granitoid magma source region may be middle, upper crust (metamorphic) sedimentary rocks, early and late Cretaceous granitic magmatic source region may be middle,Metamorphic basic igneous rocks of amphibolite facies in upper crust.Yongzhu early Jurassic peraluminous, undifferentiated S-type granites may have formed under the influence of bidirectional subduction of the Tethys ocean in Bangong Lake, Nujiang River and Yarlung Zangbo River.In the early Cretaceous undifferentiated I-type granite may have been formed under the background of the southern subduction of Bangong Lake and the Nu River Tethys, and the partial detachment of the subduction plate caused the upwelling of the asthenospheric material, which resulted in the lithospheric mantle and the middle lithosphere.The melting of the upper crust, the formation of basic and acidic magma, and the formation of magmatic mixing, the late Cretaceous undifferentiated I-type granites may have formed in the background of the collision of Gangdish-Qiangtang block and the post-collision tectonic environment.The partial delamination of thickened lithospheric mantle results in the upwelling of asthenosphere material and the formation of submersible mantle derived magma, resulting in the formation of acidic magma in the melting of the middle and upper crust, and the formation of magma mixing between the two.The dynamic background of the central and northern Gangdes in Mesozoic is mainly reflected by the subduction of the Bangong Lake-Tethys of the Nujiang River, the collision between the Gangdes and the Qiangtang landmass and the collapse after orogeny.The granites related to mineralization in Yongzhu area are of early Cretaceous and late Cretaceous, and the types of mineralization are skarn type (copper) mineralization.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P588.121

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