地学前缘 ›› 2025, Vol. 32 ›› Issue (6): 377-395.DOI: 10.13745/j.esf.sf.2025.10.57

• 岩石成因与效应新探 • 上一篇    下一篇

青藏高原南部日喀则地区中新世脉岩地球化学和岩石成因

李丽婵1(), 赵志丹1,*(), 唐演2, 刘栋1, 王珍珍1, 王青1, 朱弟成1, 莫宣学1   

  1. 1.地质过程与成矿预测全国重点实验室, 中国地质大学(北京) 地球科学与资源学院, 北京 100083
    2.中国石油大庆油田有限责任公司 成都勘探开发研究院, 四川 成都 610000
  • 收稿日期:2025-10-16 修回日期:2025-10-20 出版日期:2025-11-25 发布日期:2025-11-12
  • 通信作者: 赵志丹
  • 作者简介:李丽婵(2000—),女,硕士,矿物学、岩石学、矿床学专业。E-mail: llc973963473@163.com
  • 基金资助:
    国家重点研发计划项目(2022YFF0800901-3);国家自然科学基金项目(92479107);国家自然科学基金项目(42073035);国家自然科学基金项目(41802058);第二次青藏高原科学考察专题(2019QZKK070204);中央高校基本科研业务费(QZ05201902);国家创新引智111项目(B18048)

Geochemistry and petrogenesis of Miocene dikes in the Shigatse area, southern Tibet

LI Lichan1(), ZHAO Zhidan1,*(), TANG Yan2, LIU Dong1, WANG Zhenzhen1, WANG Qing1, ZHU Dicheng1, MO Xuanxue1   

  1. 1. State Key Laboratory of Geological Processes and Mineral Resources, and School of Earth Science and Resources, China University of Geosciences (Beijing), Beijing 100083, China
    2. Chengdu Exploration and Development Research Institute of Daqing Oilfield, China National Petroleum Corporation (CNPC), Chengdu 610000, China
  • Received:2025-10-16 Revised:2025-10-20 Online:2025-11-25 Published:2025-11-12
  • Contact: ZHAO Zhidan

摘要:

脉岩是与同期岩浆作用具有相似矿物成分的小型侵入体,在冈底斯南部发育的中新世脉岩具有不同的产状、年龄,蕴含了岩浆作用和构造作用的双重信息。本文选择了日喀则谢通门县的脉岩为研究对象,开展地球化学、年代学以及Lu-Hf同位素研究,对脉岩的成因,构造特征、源区特性和地球动力学意义进行了详细讨论。识别出脉岩的锆石U-Pb年龄为15.2~14.5 Ma,为中新世后碰撞脉岩。脉岩具有较高的MgO含量、Mg#和不相容元素含量,同时表现出高Sr、低Y和Yb、较高的Sr/Y值、富集轻稀土元素和大离子亲石元素、亏损重稀土元素和高场强元素的埃达克质岩石地球化学特征。综合地球化学特征和构造特征推测成因模式为下地壳的拆沉引发了南拉萨地体的重力垮塌,导致南北向与东西向叠加的构造伸展。拆沉至软流圈的下地壳发生部分熔融并混入地幔组分,熔体沿伸展形成的正断裂和裂谷上侵,构成时空相近的两种方向的日喀则闪长玢岩脉。

关键词: 冈底斯岩基, 南拉萨地体, 中新世, 脉岩, 埃达克质岩石

Abstract:

Dikes are small-scale intrusions with mineral compositions similar to those of contemporaneous magmatic rocks. The Miocene dikes in the southern Gangdese exhibit diverse modes and ages, recording information pertaining to both magmatism and tectonics. This study focuses on dikes in Xaitongmoin County, Shigatse, combining geochemistry, geochronology, and Lu-Hf isotopes to elucidate their petrogenesis, structural characteristics, source properties, and geodynamic implications. Zircon U-Pb dating indicates that the dikes were emplaced between 15.2 and 14.5 Ma, identifying them as post-collisional Miocene intrusions. Geochemically, these dikes exhibit high MgO, high Mg#, and elevated concentrations of incompatible elements. They also show adakitic characteristics, including high Sr, low Y and Yb, high Sr/Y ratios, enrichment in light rare earth elements (LREE) and large ion lithophile elements (LILE), and depletion in heavy rare earth elements (HREE) and high field strength elements (HFSE). Based on integrated geochemical and structural features, we propose a genetic model: delamination of the lower crust triggered gravitational collapse of the southern Lhasa terrane, leading to superimposed N-S and E-W extensional structures. The delaminated lower crust underwent partial melting upon reaching the asthenosphere and incorporated mantle components. The resulting melts ascended along the normal faults and rifts formed by extension, ultimately forming the Shigatse diorite porphyry dikes with two spatial orientations emplaced in close temporal proximity.

Key words: Gangdise batholith, South Lhasa Block, Miocene, dike rocks, adakitic rocks

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