甘肃北山地区晚三叠世煌斑岩地球化学特征及构造意义  

Geochemical Characteristics and Tectonic Significance of Late Triassic Lamprophyre in the Beishan Region,Gansu Province

作　　者：陈阳阳[1] 段俊[1] 徐刚[1] 钱壮志[1] 杨涛 刘君泰 CHEN Yangyang;DUAN Jun;XU Gang;QIAN Zhuangzhi;YANG Tao;LIU Juntai(School of Earth Sciences and Resources,Chang'an University,Xi’an 710054,Shaanxi,China;Northwest Geological Exploration Institute,China Metallurgical Geology Bureau,Xi’an 710054,Shaanxi,China;Second Geological and Mineral Exploration Institute of Gansu Provincial Bureau of Geology and Mineral Exploration,Lanzhou 730020,Gansu,China)

机构地区：[1]长安大学地球科学与资源学院,陕西西安710054 [2]中国冶金地质总局西北地质勘查院,陕西西安710054 [3]甘肃省地矿局第二勘查院,甘肃兰州730020

出　　处：《西北地质》2024年第6期78-94,共17页Northwestern Geology

基　　金：陕西省自然科学基础研究计划项目(2023-JC-YB-224);中国工程院战略研究与咨询项目(2023-XZ-20)联合资助。

摘　　要：甘肃北山地区位于中亚造山带南缘,是研究中亚造山带构造演化的关键区域。煌斑岩多为岩石圈地幔在伸展背景下低程度部分熔融形成的碱性岩石,确定其形成时代和岩石成因可为区域构造演化提供新的依据。笔者对北山地区柳园南煌斑岩进行了系统的岩石学、地球化学和锆石U-Pb年代学及Hf同位素研究。柳园南煌斑岩的锆石U-Pb年龄为(228.2±1.1)Ma(晚三叠世)。煌斑岩中富含金云母和角闪石等富挥发性组分的矿物。岩石地球化学分析表明:柳园南煌斑岩属于超钾质煌斑岩,母岩浆为碱性岩浆系列;全岩微量元素具有明显的Nb-Ta和Zr-Hf负异常,锆石εHf(t)值为0.5~4.9,平均值为+2.8,具俯冲洋壳板片流体交代特征。柳园南煌斑岩中橄榄石Mn/Fe与Ca/Fe值对比表明,柳园南煌斑岩源区为富金云母的方辉橄榄岩地幔;微量元素模拟计算表明,地幔源区具有富集的特征。因此,柳园煌斑岩岩浆源区为被俯冲板片流体交代的岩石圈地幔。结合前人对中亚造山带南缘构造演化的研究,北山南部地区在晚三叠世时已进入陆内伸展阶段,减压作用促使被俯冲流体交代的岩石圈地幔发生低程度部分熔融,形成柳园煌斑岩脉。The Beishan region is located at the southern margin of the Central Asian Orogenic Belt(CAOB)and is a key area for studying the tectonic evolution of the CAOB.Lamprophyres are the product of low-degree partial melting of the subcontinental lithospheric mantle in the extensional background.Their formation age and petrogenesis can play a significant role in ascertaining the regional tectonic evolution.In this paper,systematic petrological,geochemical and zircon U-Pb chronology and Hf isotope studies were carried out on the lamprophyre in the Liuyuan area in southern Beishan region.The zircon U-Pb age of the Liuyuannan lamprophyre is(228.2±1.1)Ma(Late Triassic).The lamprophyre is rich in volatile component minerals such as phlogopite and hornblende.The Liuyuannan lamprophyre belongs to ultrapotassic lamprophyre,and its parent magma is an alkaline magma series.The Liuyuannan lamprophyre are characterized by pronounced negative Nb-Ta and Zr-Hf anomalies,positive zirconεHf(t)values ranging from 0.5 to 4.9,with an average value of+2.8.These data indicate that the mantle source was metasomatized by the subducted melts/fluids.The Mn/Fe and Ca/Fe ratios of olivine crystals in the Liuyuannan lamprophyre indicate that the mantle source is phlogopite-rich harzburgite mantle;trace element simulations indicate that the mantle source of Liuyuannan lamprophyre is an enriched peridotite-type mantle.Therefor,the source of the Liuyuan lamprophyre should be the lithospheric mantle metasomatized by subducting slab fluids.Combined with previous studies on the tectonic evolution of the southern of the CAOB,we believe that the Beishan region has entered intracontinental extensional environment in the Late Triassic.Decompression promoted low-degree partial melting of the lithospheric mantle metasomatized by subduction fluids,resulting in the formation of the Liuyuan lamprophyre.

关 键 词：煌斑岩 晚三叠世 俯冲流体交代 陆内伸展 甘肃北山 

分 类 号：P581[天文地球—岩石学]