柴北缘都兰地区志留纪高镁闪长岩的成因及其动力学背景:锆石U-Pb年代学、地球化学和Hf同位素的制约  

PETROGENESIS AND DYNAMIC SETTING OF SILURIAN HIGH-MG DIORITES IN THE DULAN AREA,NORTHERN QAIDAM:CONSTRAINTS OF ZIRCON U-Pb CHRONOLOGY,GEOCHEMISTRY AND Hf ISOTOPE

作　　者：白兴卫 周虎[1] 刘忠媛 楚志强 黄虎[2] 熊富浩 BAI Xingwei;ZHOU Hu;LIU Zhongyuan;CHU Zhiqiang;HUANG Hu;XIONG Fuhaol(College of Earth and Planetary Science,Chengdu University of Technology,Chengdu,Sichuan 610059,China;National Key Laboratory of Oil and Gas Reservoir Geology and Eaploitation,Chengdu University of Technology,Chengdu,Sichuan 610059,China)

机构地区：[1]成都理工大学地球与行星科学学院,四川成都610059 [2]成都理工大学油气藏地质及开发工程全国重点实验室,四川成都610059

出　　处：《矿物岩石》2024年第3期25-38,共14页Mineralogy and Petrology

基　　金：国家自然科学基金青年科学基金项目(批准号:41602049);成都理工大学珠峰科学研究计划项目(编号:2023ZF11412)。

摘　　要：高镁闪长岩是探究岩浆动力学过程和大地构造演化的重要岩石探针之一。本次研究以柴北缘东段都兰地区新发现的高镁闪长岩为对象,开展岩相学、年代学、全岩地球化学和锆石Hf同位素地球化学研究,探究其成因机制及动力学背景。LA-ICP-MS锆石U-Pb年代学揭示都兰高镁闪长岩的结晶年龄为430±3Ma(MSWD=0.85,N=15),形成于晚志留世。岩石具有较低的w(SiO_(2))(52.8%~59.8%)、中等的全碱(w(Na_(2)O+K_(2)O)=4.52%~6.74%)和较高的w(Al_(2)O_(3))(16.0%~17.85%)、w(FeO^(T))(6.23%~8.10%)含量,属于钙碱性准铝质系列岩石。岩石具有高w(MgO)(3.21%~5.09%)含量、Mg^(#)(48~53)值和低Sr/Y(5.08~13.6)值的特征,属于高镁闪长岩。都兰高镁闪长岩富集Rb,Ba,Th,U,K等大离子亲石元素,亏损Nb,Ta,Ti等高场强元素,Eu负异常较弱(δEu=0.74~0.97),具有较高的Zr/Hf(33.0~45.7)、Nb/Ta(13.5~16.9)比值和亏损的锆石Lu-Hf同位素组成,以及相对较小的模式年龄(ε_(Hr)(t)=2.51~5.01,T_(DM1)=859~996Ma)。结合柴北缘变质峰期、沉积作用和岩浆活动记录,本次研究认为都兰高镁闪长岩是碰撞后板片断离背景下的岩浆产物,其岩浆起源于幔源岩浆底侵背景下的新生地壳部分熔融以及壳幔岩浆混合作用。High magnesium diorite serves as a crucial indicator for investigating magmatic dynamics and tectonic evolution.This study focuses on newly discovered high magnesium diorite from the Dulan area on the eastern part of the northern margin of Qaidam.The research utilizes petrography,chronology,whole rock geochemistry,and Hf isotope geochemistry of zircon to explore its genetic mechanisms and dynamic background.LA-ICP-MS zircon U-Pb chronology reveals that the Dulan high magnesium diorite crystal-lized at approximately 430±3 Ma(MSWD=0.85,N=15),placing its formation in the late Silurian Age.Geochemical analysis indicates that the Dulan high magnesium diorite exhibits low SiO_(2)(52.8%-59.8%),medium total alkali(Na_(2)O+K_(2)O)=4.52%-6.74%,and high Al_(2)O_(3)(16.0%-17.85%),FeO^(T)(6.23%8.10%)contents,characteristic of calc-alkaline quasi-aluminous rocks.The rocks are characterized by a high MgO content(3.21% to 5.09%),Mg^(#)values ranging from 48 to 53,and low Sr/Y ratios(5.08 to 13.6),indicating they belong to the high magnesium diorite category.These high mag-nesium diorites are enriched in large ion lithophile elements such as Rb,Ba,Th,U,and K,while show-ing depletion in high field strength elements like Nb,Ta,and Ti.They exhibit a weak negative Eu anoma-ly(8Eu=0.74 to 0.97).Zircons from these rocks display high Zr/Hf ratios(33.0 to 45.7)and Nb/Ta ra-tios(13.5 to 16.9),with depleted Lu-Hf isotopic compositions and relatively young model ages(ε_(hr)(t)=2.51 to 5.01,T_(DM1)=859 to 996 Ma).Based on a comprehensive analysis of metamorphic peaks,sedimen-tation,and magmatic activity records in the northern margin of Qaidam,the Dulan high magnesium diorite is interpreted to have formed from magma that was generated during the fragmentation of the plate slab af-ter collision events.The magma likely originated from partial melting of the neocrust,with mixing of crust-mantle magma facilitated by the invasion of mantle-derived magma.

关 键 词：柴北缘 晚志留世 碰撞后 高镁闪长岩 岩石成因 

分 类 号：P588.121[天文地球—岩石学] P595[天文地球—地质学]