北东帕米尔晚三叠世含暗色包体花岗岩成因及其地质意义  

Genesis and geological significance of Late Triassic granites and mafic enclaves in the northern East Pamir

作　　者：西艾力·阿尔肯 刘晓强 钱旭坤 木热地里·马合木提 Xiaili Aerken;Liu Xiaoqiang;Qian Xukun;Muredili Mahemuti(School of Geology and Mining Engineering,Xinjiang University,Ürümqi 830017;Xinjiang Key Laboratory for Geodynamic Processes and Metallogenic Prognosis of the Central Asia Orogenic Belt,Ürümqi 830017)

机构地区：[1]新疆大学地质与矿业工程学院,乌鲁木齐830017 [2]新疆中亚造山带大陆动力学与成矿预测自治区重点实验室,乌鲁木齐830017

出　　处：《地质科学》2025年第2期550-576,共27页Chinese Journal of Geology(Scientia Geologica Sinica)

基　　金：国家重点研发计划项目(编号:2021YFC2901904);新疆维吾尔自治区重点研发任务项目(编号:2022B03015-2)资助。

摘　　要：中央造山带西端的西昆仑—帕米尔造山带记录了较为完整的特提斯洋构造演化信息。本文对北东帕米尔木吉地区三叠纪花岗岩及其暗色包体进行了岩石学、同位素地质年代学、全岩元素和同位素地球化学研究,以期制约区内古特提斯演化。锆石U-Pb定年显示,寄主花岗岩(207.74±0.92 Ma)、花岗闪长岩(214.3±1.1 Ma)与其中闪长质岩浆成因暗色包体(208.0±1.6 Ma和209.8±1.3 Ma)均为晚三叠世岩浆活动的产物。寄主岩具有变化的SiO_(2)(58.79%~71.39%)、K_(2)O(1.99%~5.09%)和MgO(1.06%~3.63%),整体呈现准铝质—弱过铝质(A/CNK=0.97~1.11)的I型花岗岩特征。寄主岩较高的Mg#(49~52),表明其不是纯地壳源区部分熔融的产物。岩石具有富集轻稀土和大离子亲石元素(Rb、U、K、Th),亏损重稀土和高场强元素(Nb、Ta、P、Ti)的弧型微量元素特征(Nb/La=0.16~0.48)。岩石的Sr-Nd-Hf同位素表现为富集特征,(^(87)Sr/^(86)Sr)i=0.708408~0.710473,ε_(Nd)(t)=-7.15~-6.02,ε_(Hf)(t)=-5.9~-1.3。相比寄主岩,暗色包体具有较低的SiO_(2)(56.10%~58.68%)、K_(2)O(1.82%~2.04%)和较高的MgO(4.47%~5.12%),富集大离子亲石元素(Rb、U、K、Th),亏损高场强元素(Nb、Ta、P、Ti),(^(87)Sr/^(86)Sr)i=0.707921~0.708021,ε_(Nd)(t)=-6.32~-5.90,ε_(Hf)(t)=-6.9~-2.0。综合分析,木吉地区含暗色微粒包体的花岗质岩浆岩是幔源镁铁质岩浆和壳源长英质岩浆混合作用的产物,其中幔源镁铁质岩浆的母岩浆来自于俯冲板片流体交代的地幔源区,而壳源长英质熔体来源于变角闪岩古老下地壳在40~50 km地壳厚度下熔融。结合北东帕米尔晚三叠世基础地质研究进展,认为210 Ma左右北东帕米尔古特提斯洋尚未闭合。The western segment of the Central Orogenic Belt,encompassing the western Kunlun‑Pamir Orogenic Belt,harbors a relatively comprehensive record of the Tethyan tectonic evolution.This study conducts a thorough investigation of the petrology,isotope geochronology,whole‑rock elemental,and isotopic geochemistry of Triassic granites and their mafic enclaves from the Muji area in northeastern Pamir,aiming to constrain the evolutionary history of the Paleo‑Tethys.Zircon U‑Pb dating reveals that the host granite(207.74±0.92 Ma),granodiorite(214.3±1.1 Ma),and mafic enclaves(208.0±1.6 Ma and 209.8±1.3 Ma)are products of Late Triassic magmatic activities.The host rocks,characterized by high SiO_(2)(58.79%~71.39%),K_(2)O(1.99%~5.09%),and MgO(1.06%~3.63%),exhibit traits of I‑type granites,metaluminous to slightly peraluminous(A/CNK=0.97~1.11).The relatively high Mg#(49~52)of the host rocks suggests that they could not have formed solely through partial melting of crustal sources.The rocks exhibit arc‑like magmatic trace element features(Nb/La=0.16~0.48),with enrichment of light rare earth elements and large ion lithophile elements(Rb,U,K,Th),and depletion of heavy rare earth elements and high field strength elements(Nb,Ta,P,Ti).The Sr‑Nd‑Hf isotopic compositions display enriched characteristics(^(87)Sr/^(86)Sr)i=0.708408~0.710473,ε_(Nd)(t)=-7.15~-6.02,ε_(Hf)(t)=-5.9~-1.3.In contrast,the mafic enclaves exhibit lower SiO_(2)(56.10%~58.68%),K_(2)O(1.82%~2.04%)and higher MgO(4.47%~5.12%),yet similarly enriched in large ion lithophile elements(Rb,U,K,Th)and depleted in high field strength elements(Nb,Ta,P,Ti)with isotopic signatures(^(87)Sr/^(86)Sr)i=0.707921~0.708021,ε_(Nd)(t)=-6.32~-5.90,ε_(Hf)(t)=-6.9~-2.0.Comprehensive analyses suggest that the parent magma of the Muji mafic enclaves originated from partial melting of a subduction‑metasomatized,hydrated,enriched mantle wedge,while the host granites formed from the dehydration melting of ancient lower crust induced by the underplating of mafic magmas an

关 键 词：三叠纪 暗色微粒包体 岩浆混合 古特提斯洋 北东帕米尔 

分 类 号：P588.1[天文地球—岩石学] P597[天文地球—地质学]