东天山平台山复式岩体岩石成因及其对晚古生代洋脊俯冲的启示  

Petrogenesis of Pingtaishan Compound Massif in the Eastern Tianshan,NW China,and Its Implications on Late Paleozoic Ridge Subduction

作　　者：马志杰 柴凤梅 王雯[1] 毛启贵 祁冬梅 张雪冰 Ma Zhijie;Chai Fengmei;Wang wen;Mao Qigui;Qi Dongmei;Zhang Xuebing(Xinjiang Key Laboratory for Geodynamic Processes and Metallogenic Prognosis of the Central Asian Orogenic Belt,Xinjiang University,Urumqi 830049,China;School of Geology and Geomatics,Tianjin Chengjian University,Tianjin 300384,China;Xinjiang Research Center for Mineral Resources,Xinjiang Institute of Ecology and Geography,Chinese Academy of Sciences,Urumqi 830011,China)

机构地区：[1]新疆大学中亚造山带大陆动力学与成矿预测实验室,新疆乌鲁木齐830049 [2]天津城建大学地质与测绘学院,天津300384 [3]中国科学院新疆生态与地理研究所矿产资源中心,新疆乌鲁木齐830011

出　　处：《地球科学》2022年第9期3210-3228,共19页Earth Science

基　　金：国家自然科学基金项目(Nos.U1403391,42072100);国家重点研发计划项目(No.2017YFC0601201).

摘　　要：为深入了解东天山晚古生代时期的构造演化,对东天山卡拉塔格地区平台山岩体开展了系统的野外调查,并进行了锆石U-Pb年代学和地球化学研究.平台山岩体是由辉长岩、辉绿岩、角闪辉长岩和石英闪长岩组成的复式岩体.其中辉长岩和石英闪长岩的LA-ICP-MS锆石U-Pb年龄分别为284.7±2.8 Ma和270.0±3.4 Ma.辉长岩、辉绿岩和角闪辉长岩的SiO_(2)为44.17%~50.14%,Fe_(2)O_(3) T为7.63%~12.75%,MgO介于2.79%~16.80%,全碱含量低且变化大(K_(2)O+Na_(2)O=1.79%~6.36%),Mg#值变化大(41~73),富集Rb、Ba、Sr、U和Pb,亏损Nb、Ta、Zr、Hf和Ti等高场强元素,与岛弧岩浆岩特征一致.石英闪长岩具有高硅(SiO_(2)=61.15%~64.62%)、富碱(K_(2)O+Na_(2)O=8.50%~9.34%),富集Rb、Ba和Zr、Hf、Y,具有Eu、Sr和Ti负异常,并有高的(Ga/Al)×10^(4)比值(3.55~3.68)和Y/Nb比值(14.31~16.28),与A_(2)型花岗岩特征相似.辉长岩、辉绿岩和角闪辉长岩属于阿拉斯加型岩体,母岩浆来源于亏损地幔与被流体交代岩石圈地幔的混合物,石英闪长岩母岩浆来源于亏损地幔与下地壳熔体的混合物.结合区域资料,本文认为早二叠世康古尔洋尚未闭合,平台山复式岩体是康古尔洋洋脊斜向俯冲的产物.Pingtaishan intrusion located in the Kalatag area of eastern Tianshan,is a compound massif composed of gabbro,diabase,hornblende gabbro and quartz diorite,and is an ideal object to understand the tectonic evolution of the eastern Tianshan during the Late Paleozoic.LA-ICP-MS zircon U-Pb geochronology and geochemical analysis of major and trace elements are performed to unravel their petrogenesis.The gabbro,diabase and hornblende gabbro exhibit low SiO_(2)(44.17%-50.14%)and high Fe_(2)O_(3)^(T)(7.63%-12.75%),and variable alkali content(K_(2)O+Na_(2)O=1.79%-6.36%),MgO content(2.79%to 16.80%)and Mg^(#)(41-73).In addition,these rocks are enriched in Rb,Ba,Sr,U,and Pb and depleted in Nb,Ta,Zr,Hf,and Ti,which is consistent with the characteristics of island arc magmatism.The quartz diorites exhibit high SiO_(2)(61.15%-64.62%)and total alkali(K_(2)O+Na_(2)O=8.50%-9.34%)content,enriched in LILEs(Rb and Ba)and HFSEs(Zr,Hf and Y),high(Ga/Al)×10^(4)ratios(3.55 to 3.68)and Y/Nb ratios(14.31 to 16.28),depleted in Eu,Sr and Ti.Quartz diorites features exhibit an affinity with A^(2)-type granites.On the one hand,these gabbro,diabase,and hornblende gabbro belong to the Alaskan-type mafic complexes,and their parental magma is derived from a mixture of depleted mantle and metasomatized lithospheric mantle.On the other hand,the parental magma of quartz diorite originates from the mixing of the depleted mantle and the lower crust.Collectively,we suggest that the Pingtaishan compound massif results from the oblique subduction of the Kangguer Ocean ridge,implying that the Kangguer Ocean was not yet closed in the Early Permian.

关 键 词：复式岩体 阿拉斯加型岩体 A2型花岗岩 锆石U‐Pb定年 洋脊俯冲 东天山 地球化学 

分 类 号：P581[天文地球—岩石学]