西昆仑奇台达坂北中新世石英二长岩侵入岩年代学、地球化学及其构造意义  

Geochronology,Geochemistry and Tectonic Significance of Miocene Quartz Monzonite from the Northern of Qitai Mountain in Western Kunlun

作　　者：代新宇 周斌 李新林 杜彪 范鹏 赵江林 杨文博 武忠山 DAI Xinyu;ZHOU Bin;LI Xinlin;DU Biao;FAN Peng;ZHAO Jianglin;YANG Wenbo;WU Zhongshan(Shaanxi Institute of Geological Survey,Xi’an 710054,Shaanxi,China;Shaanxi Geological Survey Planning Research Center,Xi’an 710068,Shaanxi,China)

机构地区：[1]陕西省地质调查院,陕西西安710054 [2]陕西省地质调查规划研究中心,陕西西安710068

出　　处：《西北地质》2024年第4期191-205,共15页Northwestern Geology

基　　金：中国地质调查局项目“新疆西昆仑地区1∶5万I44E002006等四幅区调”(1212011220654);陕西省地质勘查基金“陕西典型小岩体成矿预测与勘查示范”(61201908334)联合资助。

摘　　要：奇台达坂位于新疆西昆仑新藏公路540 km处,在其北侧分布有小规模的中酸性侵入岩,呈NE向展布,岩性主要为石英二长岩。笔者以西昆仑地区东段奇台达坂北石英二长岩侵入体为研究对象,进行岩石地球化学、锆石LA-ICP-MS U-Pb年代学分析。结果表明,石英二长岩锆石U-Pb年龄加权平均值为(10.4±0.2)Ma,形成时代为中新世;岩石具有高SiO_(2)(63.16%~68.20%)、贫Al2O3(13.39%~15.47%)、高K_(2)O(4.23%~5.24%)、低MgO(1.06%~1.49%)、低TiO_(2)(0.60%~0.83%)、准铝质(A/CNK=0.83~0.90)的地球化学性质,具有A型花岗岩特征;富集K、Rb、Th、U而亏损Ba、Sr等大离子亲石元素,相对亏损Nb、Ta、Ti等高场强元素,δEu具明显的负异常特征。岩石的地球化学特征和构造环境判别图解均指示,石英二长岩可能形成于深部岩石圈强烈伸展的环境下,地壳深部形成高温低压环境,促使下地壳发生低程度部分熔融并沿深大断裂快速上升侵位,代表了板内伸展背景作用下的岩浆响应。Qitai Mountain is located in Xinjiang-Xizang Highway 540 km west of Xinjiang Kunlun area,there are small-scale medium acid intrusive rocks distributed around it,the lithology is mainly composed of the quartz monzonite.Here we present bulk-rock geochemistry,zircon U-Pb geochronology of the Miocene quartz mon-zonite in Qitai Mountain in Western Kunlun in order to shed light on this issue.Zircon U-Pb dating yielded Miocene ages of(10.4±0.3)Ma.Geochemically,this early Miocene quartz monzonite is A-type granites with high SiO_(2)(63.16%~68.20%),K_(2)O(4.23%~5.24%),and low Al2O3(13.39%~15.47%),MgO(1.06%~1.49%),TiO_(2)(0.60%~0.83%).They are enriched in light rare earth elements(LREEs),large ion lithophile ele-ments(LILEs,including K,Rb,Th,U,Ba and Sr),but depleted in high-field strength elements(Nb,Ta and Ti)and heavy rare earth elements(HREEs),and have obvious negative Eu anomalies.The geochemical characteris-tics of the rocks and the tectonic setting diagram indicate that the quartz monzonites may have been formed in an environment where the deep lithosphere was strongly extended,and a high temperature and low pressure envi-ronment was formed in the deep crust,which prompted a low degree of partial melting of the lower crust and rapid along deep and large faults.The uplift emplacement represents the magmatic response to the intraplate ex-tensional background.We suggest that the Miocene magmas from the northern of Qita Mountain in Western Kunlun were likely sourced from low-degree partial melting of the lower crust with a high temperature and low pressure environment,there may have formed in the background of strong extension of the deep lithosphere,which promotes the magmas rapid uplift along deep and large faults.

关 键 词：奇台达坂北 锆石U-PB年代学 地球化学 板内伸展 

分 类 号：P588.12[天文地球—岩石学] P597[天文地球—地质学]