地学前缘 ›› 2024, Vol. 31 ›› Issue (6): 261-281.DOI: 10.13745/j.esf.sf.2023.11.61

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藏北中仓地区晚白垩世岩浆岩成因及其对高原早期隆升的指示

吴浩1,2(), 杨晨1, 吴彦旺3, 李才4, 刘飞1, 林兆旭1   

  1. 1.桂林理工大学 广西隐伏金属矿产勘查重点实验室, 广西 桂林 541006
    2.桂林理工大学 广西战略性关键矿产资源成矿与勘查科技创新基地, 广西 桂林 541006
    3.天津城建大学 地质与测绘学院, 天津 300384
    4.吉林大学 地球科学学院, 吉林 长春 130061
  • 收稿日期:2023-08-07 修回日期:2023-11-27 出版日期:2024-11-25 发布日期:2024-11-25
  • 作者简介:吴 浩(1989—),男,副教授,主要从事岩石大地构造研究工作。E-mail: wuhaojlu@126.com
  • 基金资助:
    国家自然科学基金项目(42303045);广西科技基地和人才专项(桂科AD21220033);山东省自然科学基金资助项目(ZR2020QD045)

Petrogenesis of Late Cretaceous magmatic rocks in the Zhongcang area of northern Tibet and their implications for early uplift of the plateau

WU Hao1,2(), YANG Chen1, WU Yanwang3, LI Cai4, LIU Fei1, LIN Zhaoxu1   

  1. 1. Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration, Guilin University of Technology, Guilin 541006, China
    2. Guangxi Science Innovation Base for Formation and Exploration of Strategic Critical Mineral Resources, Guilin University of Technology, Guilin 541006, China
    3. School of Geology and Geomatics, Tianjin Chengjian University, Tianjin 300384, China
    4. College of Earth Sciences, Jilin University, Changchun 130061, China
  • Received:2023-08-07 Revised:2023-11-27 Online:2024-11-25 Published:2024-11-25

摘要:

青藏高原中部白垩纪晚期爆发了大规模的岩浆活动,并伴随着快速的地表隆升,然而其深部动力学机制一直存有较大的争议。本文对藏北中仓地区发育的闪长玢岩和英安岩开展了锆石U-Pb定年、全岩主微量元素和Sr-Nd-Hf同位素分析研究,以期为区域构造—岩浆演化提供新的约束。锆石U-Pb定年结果表明闪长玢岩和英安岩均形成于晚白垩世(90~85 Ma),其中闪长玢岩具有高Sr含量、低Y含量和高Sr/Y值的特点,显示与埃达克岩的亲缘性,结合其较高的Mg#,研究认为是增厚榴辉岩相下地壳熔体混染地幔物质的产物。英安岩地球化学和同位素特征与闪长玢岩相似,反映了相同的岩浆源区,然而其强烈亏损Rb、Ba和Sr等易蚀变元素表明成岩后期经历了强烈蚀变作用。结合区域上同时期富Mg埃达克质岩浆爆发和大规模磨拉石沉积,本文认为青藏高原中部晚白垩世构造—岩浆活动形成于班公湖—怒江缝合带碰撞后增厚下地壳拆沉过程,而深部拆沉同时触发了地表快速抬升,并由此形成了白垩纪古高原,为现代高原的形成奠定了基础。

关键词: 班公湖—怒江缝合带, 晚白垩世, 岩石成因, 拆沉作用, 高原隆升

Abstract:

During the late Cretaceous, extensive magmatic activity erupted in the central Tibetan Plateau, accompanied by rapid surface uplift. However, the deep dynamical mechanisms behind this phenomenon have been a subject of considerable debate. This study conducts U-Pb zircon dating, as well as analyses of whole-rock major and trace elements and Sr-Nd-Hf isotopes on the diorite and rhyolite developed in the Zhongcang area of northern Tibet, aiming to provide new constraints on regional tectonic-magmatic evolution. The U-Pb zircon dating results indicate that both the diorite and rhyolite formed in the Late Cretaceous (90—85 Ma). The geochemical characteristics of the diorite show high Sr, low Y content, and high Sr/Y ratios, indicating an affinity to adakite. Combined with its high Mg#, it is proposed to be a product of the mixing of underplated eclogite-facies lower crustal melts with mantle materials. The geochemical and isotopic characteristics of the rhyolite are similar to those of the diorite, reflecting a common magmatic source. However, its significant depletion in Rb, Ba, Sr, and other easily altered elements suggests it underwent intense alteration during the late diagenesis. Coupled with the contemporaneous eruption of high-Mg adakitic magma and large-scale molasse deposition in the region, this study posits that the tectonic-magmatic activity in the central Tibetan Plateau during the Late Cretaceous was a result of the thickening and detachment of the lower crust following the collision of the Bangong Lake—Nujiang suture zone. This deep detachment simultaneously triggered rapid surface uplift, forming a Cretaceous paleo-plateau and laying the foundation for the modern plateau’s formation.

Key words: Bangong Lake—Nujiang suture zone, Late Cretaceous, rock genesis, detachment, plateau uplift

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