| 拉萨地块北缘早白垩世晚期地壳生长:来自改则亚多～106Ma侵入岩的证据 |
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| 引用本文： | 董瀚,苟国宁,齐玥,段凯,张志平,吴勇,焦世文,郝露露,陈福坤,王强.拉萨地块北缘早白垩世晚期地壳生长:来自改则亚多～106Ma侵入岩的证据[J].大地构造与成矿学,2016(6):1226-1238. |
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| 作者姓名： | 董瀚 苟国宁 齐玥 段凯 张志平 吴勇 焦世文 郝露露 陈福坤 王强 |
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| 作者单位： | 1. 甘肃省地矿局第三地质矿产勘查院,甘肃兰州,730050;2. 中国科学院广州地球化学研究所,同位素地球化学国家重点实验室,广东广州510640;中国科学院大学,北京100049;3. 中国科学技术大学地球与空间科学学院,壳幔物质与环境重点实验室,安徽合肥230026;4. 中国科学院广州地球化学研究所,同位素地球化学国家重点实验室,广东广州510640 |
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| 基金项目： | 西藏改则县岗嘎地区1∶5万(144E022022、I44E022023、I44E023022、I44E023023)4幅区域地质矿产调查，国家重点研发计划课题(2016YFC0600407)，中国科学院战略性先导科技专项(B类)(XDB03010600)，国家自然科学基金重点项目(41630208)，广东省项目(2014TX01Z079)，中国科学院广州地球化学研究所项目(GIGCAS135项目135TP201601) |
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| 摘 要： | 北部拉萨地块晚中生代的地壳生长时间和机制存在争论。本文报道了北部拉萨地块的改则亚多侵入体的年代学、地球化学资料。改则亚多侵入体形成于早白垩世晚期(~106 Ma),其岩石类型包括二长闪长岩、闪长岩、花岗闪长斑岩、花岗斑岩。岩石属于钙碱性系列岩石,显示轻稀土富集,Nb和重稀土亏损,其中花岗闪长斑岩、花岗斑岩显示了埃达克质岩的地球化学特征。主体岩石样品具有一致的εNd(t)(2.65~1.42)和(~(87)Sr/~(86)Sr)i(0.7045~0.7049)。二长闪长岩、闪长岩由俯冲流体交代的地幔橄榄岩熔融产生的玄武质岩浆经过地壳混染和分离结晶作用形成。花岗闪长斑岩、花岗斑岩由增厚的新底侵玄武质下地壳熔融形成。早白垩世晚期(118~105 Ma),俯冲的班公湖–怒江特提斯洋岩石圈板片后撤过程中,诱发软流圈上涌,导致其上覆地幔熔融或其自身发生减压熔融,来自亏损地幔的岛弧岩浆连续底侵加入到北部拉萨地块的地壳或喷出地表,导致了该区在晚中生代的地壳生长。
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| 关 键 词： | 地壳生长 底侵 板片后撤 拉萨地块 青藏 |
Late Early Cretaceous Crustal Growth in Northern Lhasa Block:Evidence from ca.106 Ma Intrusive Rocks in the Yaduo Area,Gerze County |
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| Abstract: | The time and mehanism for Late Mesozoic crustal growth in the northern Lhasa Block are controversial.This study presents zircon U-Pb age and whole-rock geochemical data for the Yaduo intrusion.The Yaduo intrusive rocks were generated in the Late Early Cretaceous (ca.106 Ma),and consist of monzodiorite,diorite,granodiorite porphyry,and granite porphyry.They are calc-alkaline,and characterized by enrichment of light rare earth element and depletion of Nb and heavy rare earth element,and constant εNd(t) (2.65-1.42) and (87Sr/86Sr)i (0.7045-0.7049) values.We suggest that the monzodiorite and diorites were generated by crustal assimilation and fractional crystallization of basaltic magmas derived from metasomatized mantle peridotites.The granodiorite and granite porphyries are geochemically similar to the adakites.They were derived from partial melting of the thickened and newly underplated basaltic lower crust.In the late stage of Early Cretacous (118-105 Ma),the roll-back of subducted Bangong-Nujiang Tethyan oceanic lithospheric slab triggered the upwelling of asthenosphere,which caused the partial melting of overlying mantle or decompressional melting of the subducting slab.The continuous underplating as well as the eruption of depleted mantle-derived magmas in northern Lhasa caused the Late Mesozoic crustal growth. |
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| Keywords: | crustal growth underplating slab roll back Lhasa Tibet |
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