东昆仑马尼特地区片麻状花岗闪长岩锆石U-Pb年代学、地球化学及其构造背景

发布时间：2018-08-04 10:08

【摘要】：为确定东昆仑马尼特地区片麻状花岗闪长岩的形成时代、源区性质和构造背景,对其进行了锆石U-Pb年代学、地球化学和锆石Hf同位素研究.本次测试的片麻状花岗闪长岩锆石LA-ICP-MS(laser ablation inductively coupled plasma mass spectrometry)U-Pb加权平均年龄为495.6±1.1Ma(MSWD=0.13),属于晚寒武世.马尼特片麻状花岗闪长岩SiO_2含量为61.47%~63.99%,Na_2O、K_2O和CaO含量分别为2.91%~3.64%、0.93%~2.31%和4.29%~6.52%,全碱ALK=3.92%~5.69%,铝饱和指数A/CNK=0.83~0.97,属准铝质钙碱性系列岩石.岩石具有富集大离子亲石元素(Rb、K)和不相容元素(Th、U),相对亏损Nb、Ta、Zr、Ti高场强元素的特征,Nb/Ta、La/Nb、Th/Nb、Th/La等比值显示出岩石具有壳源特征.岩石具有高的εHf(t)值(12.2~15.0),Hf两阶段模式年龄在506~662Ma范围内,其岩浆源区初始物质主要来源于新生地壳.岩石在微量元素Rb-(Y+Nb)构造判别图落入火山弧花岗岩区域,在R1-R2构造判别图落入板块碰撞前消减区花岗岩区域.结合岩石成岩年龄、地球化学特征以及区域构造演化,推测其应形成于原特提斯洋俯冲的构造环境,属于大洋洋壳向南俯冲的产物,即柴达木地块和万宝沟大洋玄武岩高原之间的洋壳同时向南、北发生双向俯冲消减.
[Abstract]:In order to determine the age, source and tectonic setting of the granodiorite in Manitte, East Kunlun, zircon U-Pb geochronology, geochemistry and HF isotope of zircon have been studied. The zircon LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometry) U-Pb weighted average age of granodiorite measured in this paper is 495.6 卤1.1Ma (MSWD=0.13), which belongs to the late Cambrian. The SiO_2 content of Manitt granodiorite is 61.47 and 63.99, and the content of Na _ 2o _ 2O _ K _ 2O and CaO is 2.91 ~ 3.64 and 2.931%, respectively, and 2.31% and 4.29 ~ 6.52% respectively. The total alkali-ALKN _ (3.92) diorite is 5.69, and the aluminum saturation index (A _ (%) CNK _ (0.83N) _ (0.97) belongs to the quasialuminous calc-alkaline series rocks. The rocks are characterized by the enrichment of large ion lithophile elements (RbNK) and incompatible elements (Thu) and the relative depletion of high field strength elements such as NB / Tae Ta-ZrZr Ti. The ratios of NB / Ta / La / NbTh/ NbTH / Th-La show that the rocks have the characteristics of crust-source. The rocks have a high 蔚 Hf (t) (12.2N 15.0) two-stage model age in the range of 506~662Ma, and the initial material of the magmatic source region is mainly derived from the new crust. The trace element Rb- (Y Nb) tectonic discriminant diagram falls into the volcanic arc granite area, and the R1-R2 tectonic discriminant diagram falls into the granite area of the subduction zone before the plate collision. In combination with the age of diagenesis, geochemical characteristics and regional tectonic evolution, it is inferred that they were formed in the tectonic environment of the original Tethys ocean subduction and belong to the subduction products of the oceanic crust towards the south. That is, the oceanic crust between Qaidam block and Wanbaogou oceanic basalt plateau simultaneously faces south and north.
【作者单位】：吉林大学地球科学学院;
【基金】：中国地质调查局地质大调查项目(No.12120111086020)
【分类号】：P588.12;P597.3

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