祁漫塔格阿确墩地区花岗岩岩石成因:来自锆石U-Pb年代学、地球化学及Hf同位素的制约  

Origin of Granites from A’quedun Area in Qimantage Mountains:Constraints from Zircon U-Pb Dating,Geochemistry and Hf Isotope

作　　者：王月飞 李猛[2,3] 查显锋[2,3] 胡朝斌[2,3] 李瑶 高晓峰 Wang Yuefei;Li Meng;Zha Xianfeng;Hu Chaobin;Li Yao;Gao Xiaofeng(School of Earth Science and Resources,Chang'an University,Xi'an 710054,China;Xi'an Center of Geological Survey,Orogen Research Center,China Geological Survey,Xi'an 710054,China;ey Laboratory for the Study of Focused Magmatism and Giant Ore Deposits,Ministry of Land and Resources,Xi'an 710054,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]中国地质调查局西安地质调查中心,造山带地质研究中心,陕西西安710054 [3]国土资源部岩浆作用成矿与找矿重点实验室,陕西西安710054

出　　处：《地球科学》2018年第12期4319-4333,共15页Earth Science

基　　金：长安大学高校基金项目(No.300102278401);国家科技支撑课题(No.2015BAB05B01);中国地质调查局项目(No.DD20160002);陕西省青年科技新星支撑项目(No.2013KJXX-68)

摘　　要：祁漫塔格阿确墩地区花岗岩的形成背景对东昆仑加里东期碰撞-伸展过程具有重要制约意义.阿确墩地区泥盆纪侵入岩主要由花岗闪长岩和英云闪长岩组成,锆石U-Pb定年结果显示,花岗闪长岩和英云闪长岩形成年龄分别为385±5Ma和393±5Ma,为中泥盆世岩浆活动的产物.花岗闪长岩的SiO2含量为63.56%~66.57%,Mg^#为0.31~0.35,K2O/Na2O比值为0.49~0.66,铝饱和指数A/CNK值为0.95~1.02,富集Rb、Ba和LREE,亏损Nb-Ta、Sr、P和Ti等元素,具有明显Eu负异常(δEu=0.38~0.98).相对于花岗闪长岩,英云闪长岩具有较高的SiO2含量(67.93%~70.76%),K2O/Na2O值近于1(0.70~1.04),Mg^#为0.22~0.33,铝饱和指数A/CNK值介于0.99~1.02,在稀土和微量元素标准化图解上,富集LREE和LILEs(Rb、Ba),亏损HFSEs(Nb-Ta、P和Ti)元素,但表现出更为明显的LREE/HREE分异、弱的铕负异常或无异常(δEu=0.80~1.06),并具有较为宽泛的锆石Hf同位素组成εHf(t)=+1.91^+15.63,TDM2(Hf)=0.53~1.28Ga).区域地质研究表明,祁漫塔格地区在中泥盆世期间处于后碰撞伸展环境,阿确墩地区花岗质岩石为俯冲板片折返机制下,诱发的幔源基性岩浆同化混染古老地壳物质部分熔融形成,花岗闪长岩和英云闪长岩熔融压力条件随时间变化表明,中泥盆世期间区域仍然处于地壳厚度持续减薄的过程.The background of the formation of granite in the A'quedun area of the Qimantage Mountains has important constraints to collision-extension process on the Caledonian, in the East Kunlun Mountains. The A-quedun intrusive rocks mainly consist of granodiorite and tonalite. Zircon LA-ICP-MS U-Pb dating results show that granodiorite and tonalite were formed at 385±5 Ma and 393±5 Ma respectively, which should be the product of magmatism in the Middle Devonian. The granodiorites have low SiO2 (63.56%-66.57%), Mg^# (0.31-0.35), K2O/Na2O ratios (0.49-0.66) and A/CNK (0.95-1.02), characterized by moderate LREE/HREE fractionation, strong LILE enrichment and depleted Nb-Ta, P, Ti and Eu depletion (δEu= 0.38- 0.98). Relative to the granodiorites, the tonalities have high contents of SiO2 (67.93%-70.76%) and low Mg^# (0.22-0.33), stronger LREE/HREE fractionation, Nb-Ta, Ti and weakly Eu depletion (δEu=0.80-1.06). The tonalites have positiveHf(t) values (+1.91^+15.63), and broadly two stages Hf model-ages (TDM2(Hf)=0.53-1.28 Ga). Based on the regional geological data, the East Kunlun Qimantage area was in post-collision extension stage during the Middle Devonian. The A-quedun granitic rocks derived from mantle magma assimilation contamination ancient crust in a mechanism for the exhumation of the subducted slab. The granodiorite and tonalite melt pressure changes with time, showing that the crustal thickness is still in continuous thinning process during the Middle Devonian.

关 键 词：花岗岩 岩石成因 中泥盆世 祁漫塔格 东昆仑 地球化学 

分 类 号：P581[天文地球—岩石学]