喜马拉雅造山带中段亚东地区石榴角闪岩的成因:岩石学和锆石U- Pb年代学
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本文为国家自然科学基金项目(编号41872070)、中国地质局地质调查项目(编号DD20190059)和中国地质科学院地质研究所基本科研业务费(编号J2006)联合资助的成果


Petrogenesis of the garnet amphibolites in the Yadong area of the central Himalaya: Petrology and zircon U- Pb geochronology
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    摘要:

    喜马拉雅造山带中段出露的基性麻粒岩是理解印度大陆前喜马拉雅期演化历史和新生代碰撞造山作用的理想研究对象。本文对亚东多庆湖地区的石榴角闪岩进行了岩石学、全岩主微量元素地球化学和锆石U- Pb年代学研究,揭示了其原岩类型和新生代的变质作用过程。石榴角闪岩的原岩很可能为新元古代(~890 Ma)的玄武岩,具有E- MORB型岩石的地球化学特征。石榴角闪岩具有三期矿物组合:① 进变质矿物组合可能为石榴子石+角闪石+斜长石+钛铁矿+石英,即石榴子石核部及其中包裹体;② 峰期矿物组合为石榴子石+角闪石+斜长石+黑云母+石英,即石榴子石边部和基质矿物;③ 退变质矿物组合为角闪石+斜方辉石+斜长石+黑云母+石英,包括退变质域和石榴子石边部的后成合晶矿物。矿物温压计和相平衡模拟表明,石榴角闪岩进变质、峰期和退变质条件分别为609~621℃和0. 59~0. 65 GPa、805~845℃和0. 91~1. 04 GPa、825~840℃和0. 61~0. 68 GPa,经历了峰期高压麻粒岩相的变质作用。锆石U- Pb年代学研究表明,石榴角闪岩的峰期变质时间为34. 8~20. 3 Ma,退变质时间为18. 1~17. 7 Ma,可能经历了一个较长期的部分熔融过程。本文研究认为,亚东石榴角闪岩是印度板块向欧亚板块长期俯冲、地壳增厚成因的基性麻粒岩,原岩可能与Rodinia超大陆拼合相关;其以加热埋藏、近等温降压为特征的顺时针P- T轨迹指示了喜马拉雅造山带中段的大喜马拉雅岩系上部构造层位经历了长期持续的地壳增厚和高温麻粒岩相变质作用,以及早中新世(21~17 Ma)相对快速的减压抬升和随后(17 Ma之后)相对缓慢的折返至地表的演化过程。

    Abstract:

    The basic granulites in the central Himalaya provide insights into the tectonic evolutionary history of both the pre- Himalayan of the Indian continent and the Himalayan collisional orogeny in the Cenozoic. Here, we conduct a petrological, bulk rock major- trace geochemical and zircon U- Pb geochronological study on the garnet amphibolites in the Duoqinghu of Yadong area, revealing their protoliths and Cenozoic metamorphism. The protoliths of the garnet amphibolites are probably the Neoproterozoic (~890 Ma) basalt with E- MORB geochemical characteristics. The garnet amphibolites have three- stage mineral assemblages. The early prograde metamorphic mineral assemblage is garnet+amphibole+plagioclase+ilmenite+quartz, which includes the core of garnet and inclusions within the core of garnet porphyroclast. The peak metamorphic mineral assemblage is garnet+amphibole+plagioclase+biotite+quartz, including the garnet rim and matrix minerals. The retrograde metamorphic mineral assemblage is amphibole+orthopyroxene+plagioclase+biotite+quartz, which is represented by the symplectitic minerals surrounding the garnet rim and retrograde domain. Conventional thermobarometry and phase equilibria modeling show that the prograde, peak and retrograde metamorphic conditions of garnet amphibolites are 609~621℃ and 0. 59~0. 65 GPa, 805~845℃ and 0. 91~1. 04 GPa, and 825~840℃ and 0. 61~0. 68 GPa, indicating that the garnet amphibolites have experienced peak high pressure and high temperature granulite- facies metamorphism. The zircon U- Pb geochronology shows that the peak and retrograde metamorphic ages of garnet amphibolites are 34. 8~20. 3 Ma and 18. 1~17. 7 Ma, indicating a prolonged melting episode. These results show that the garnet amphibolites are products formed during the long- lived subduction and crustal thickening of the Indian continental crust beneath the Euro- Asian plate, and their protoliths may be related to the Rodinia supercontinent convergence event. The clockwise P- T path of garnet amphibolites characterized by the burial heating and then near isothermal decompression indicates that the upper structural level of the Greater Himalayan Sequence (GHS) in the central Himalaya experienced long- lived crustal thickening and high- temperature granulite- facies metamorphism. Moreover, the upper structural level of the GHS uplifted at a relatively rapid rate (3. 0~4. 5 mm/a) in the early Miocene at ca. 21~17 Ma, but a relatively slower rate (1. 1~1. 3 mm/a) after 17 Ma.

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韩彦超,董昕,田作林.2023.喜马拉雅造山带中段亚东地区石榴角闪岩的成因:岩石学和锆石U- Pb年代学[J].地质学报,97(8):2495-2511.
HAN Yanchao, DONG Xin, TIAN Zuolin.2023. Petrogenesis of the garnet amphibolites in the Yadong area of the central Himalaya: Petrology and zircon U- Pb geochronology[J]. Acta Geologica Sinica,97(8):2495-2511.

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  • 收稿日期:2022-08-20
  • 最后修改日期:2022-10-01
  • 录用日期:2022-10-02
  • 在线发布日期: 2023-08-29
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