东昆仑东段可日正长花岗岩年龄和岩石成因对东昆仑中三叠世构造演化的制约  

Age and lithogenesis of Keri syenogranite from eastern part of East Kunlun Orogenic Belt: Constraint on the Middle Triassic tectonic evolution of East Kunlun

作　　者：陈国超 裴先治[1] 李瑞保 李佐臣 刘成军 陈有炘 裴磊[3] 李小兵[1] CHEN GuoChao1,2, PEI XianZhi1 , LI RuiBao1 , LI ZuoChen1, LIU ChengJun1 , CHEN YouXin1 , PEI Eel3 , LI XiaoBing1(1. MOE Key Laboratory of Western China＇ s Mineral Resources and Geological Engineering, Key MLR Laboratory for the study of Focused Magmatism and Giant Ore Deposits, Faculty of Earth Science and Resources, Chang＇ an University, Xi＇ an 710054, China;2. Nanyang lnstitutte of Technology, Nanyang 473000, China; 3. School of Earth Science and Resource, China University of Geoseiences, Beijing 100083, Chin)

机构地区：[1]长安大学地球科学与资源学院、西部矿产资源与地质工程教育部重点实验室、国土资源部岩浆作用与找矿重点实验室,西安710054 [2]南阳理工学院,南阳473000 [3]中国地质大学地球科学与资源学院,北京100083

出　　处：《岩石学报》2018年第3期567-585,共19页Acta Petrologica Sinica

基　　金：本文受国家自然科学基金项目(41472191、41502191、41172186、40972136)、中央高校基本科研业务费专项资金项目(310827161002、310827161006)和青海省国土资源厅冲国铝业公司公益性区域地质矿产调查基金项目(200801)联合资助.致谢感谢高景民、吴树宽和魏方辉等师弟在野外工作的帮助;特别感谢两位匿名评审老师和编辑部俞良军老师所提的宝贵修改意见使本文更加完善.

摘　　要：可日岩体位于东昆仑造山带东段东昆北构造带,岩性为含暗色微粒包体正长花岗岩。LA-ICP-MS锆石U-Pb同位素定年结果显示寄主岩和暗色微粒包体的结晶年龄分别为231.58±0.49Ma和232.6±2.3Ma。可日正长花岗岩主体为弱过铝质中钾钙碱性I型花岗岩,具有较高的SiO_2含量(72.06%~74.49%)和Na_2O/K_2O(1.00~1.35)、Nb/Ta(15.4~27.9)比值,较低的值(14~31)和Rb/Ba(0.10~0.46)比值,富集大离子亲石元素(LILE),亏损高场强元素(HFSE)。岩体为巴颜喀拉地块同东昆仑地块碰撞后,板片断离持续作用产生的镁铁质熔体底侵中下地壳使其部分熔融的结果。暗色微粒包体同寄主岩具有相近的结晶年龄、较细粒度、含有寄主岩捕获晶、针状磷灰石,显示包体是镁铁质岩浆注入寄主岩快速冷却的产物。由于寄主岩分离结晶,残留熔体与包体的浓度梯度差导致元素扩散,使两者具有物质交换。东昆仑东段晚古生代-早中生代幔源岩浆对花岗质岩浆的影响是一个持续的过程,从俯冲阶段早期流体交代地幔熔融,到俯冲阶段后期板片断离,然后同碰撞阶段板片断离的持续影响,再到后碰撞阶段加厚地壳的拆沉作用,由于地球动力学体制不同,导致幔源岩浆影响的大小和特征不同。可日岩体年龄及岩石成因显示东昆仑地区在232Ma左右处于同碰撞阶段。The Keri pluton located in the north tectonic belt of the eastern part of East Kunlun Orogenic Belt, is mainly syenogranite contained with mafic microgranular enclaves （MMEs）. The LA-ICP-MS zircon U-Pb chronology of host rock and MMEs yield an age of 231.58±0.49Ma and 232.6±2.3Ma respectively. Keri pluton is weakly peraluminous I-type granite, and belongs to middle-K calc-alkaline series. Keri pluton are high in SiO2 （72.06%-74.49%）, Na2O/K2O （1.00-1.35） and Nb/Ta （15.4-27.9）, and relatively low in Mg^# （14-31） and Rb/Ba （0.10-0.46）. The rocks generally have a similar variation trend, such as systematic enrichment of LILE and depletion of HFSE. Keri pluton is a result of partial melting of the middle-lower crust, due to the underplating of the mafic melt caused by the plate break-off after the collision between Bayan Har block and East Kunlun block. The MMEs is similar to its host rock in crystallizing age, but the size is relatively finer. The MMEs contain a few phenocrys captured from the host rock, and some acicular apatites. Above evidences suggest the MMEs is the result of the rapid condensation of mafic melt after infusing into the host rock. Due to the fractional crystallization, the concentration gradient differences between the relic melt and MMEs lead to the element diffusion, cause the interchange of material in them. The influence to the granitoid melts by the Late Palozoic-Early Mesozoic mantle-derived magma of East Kunlun is a continuous process, which was from the mantle melting with fluid metasomatism in early subduction stage to the large-scale plate break-off in late subduction atage, from the continuous influence of plate break-off in syn-collision stage to delamination of thicken crust in post-collision stage. The influence degrees and features of mantle-derived magma were different in the different geodynamic system of the process. The age and lithogenesis of Keri pluton indicate a syn-collision stage in 232Ma of East Kunlun.

关 键 词：东昆仑造山带 可日正长花岗岩 暗色微粒包体 中三叠世 

分 类 号：P599.121[天文地球—地球化学] P597.3[天文地球—地质学]