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  

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

作　　者：吴浩 杨晨 吴彦旺 李才[4] 刘飞 林兆旭 WU Hao;YANG Chen;WU Yanwang;LI Cai;LIU Fei;LIN Zhaoxu(Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration,Guilin University of Technology,Guilin 541006,China;Guangxi Science Innovation Base for Formation and Exploration of Strategic Critical Mineral Resources,Guilin University of Technology,Guilin 541006,China;School of Geology and Geomatics,Tianjin Chengjian University,Tianjin 300384,China;College of Earth Sciences,Jilin University,Changchun 130061,China)

机构地区：[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

出　　处：《地学前缘》2024年第6期261-281,共21页Earth Science Frontiers

基　　金：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)。

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。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(9085 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.

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 

分 类 号：P588.13[天文地球—岩石学] P588.14[天文地球—地质学] P597P542.5