摘要
大干沟花岗岩体位于东昆仑金水口地区,其岩石类型主要为中粗粒正长花岗岩。该花岗岩的SiO_2含量为68.68%~71.12%,平均含量为69.84%;Al_2O_3含量为14.01%~15.40%,平均含量为14.82%;K_2O/Na_2O值高,为1.19~1.64,平均为1.40;铝饱和指数A/CNK值为0.98~1.02,平均为1.00,具有准铝质-弱过铝质花岗岩的特点。岩石稀土元素总量较高,LREE元素富集,具有明显的Eu负异常,相对原始地幔明显富集U、Th,亏损Ti、P、Nb、Ta等高场强元素和Ba、Sr等大离子亲石元素,具有A型花岗岩的特征。花岗岩εNd(t)<0,为-5.6^-7.3,tDM=1.54~2.27 Ga,表明其物源可能主要为中元古代物质(金水口群),LA-ICP-MS锆石εHf(t)=-2.2~2.6,显著不同于地壳岩浆的Hf同位素组成,显示有地幔物质添加。LA-ICP-MS锆石U-Pb年龄为392±2 Ma(MSWD=1.14)。结合区域构造演化和上述地球化学特征,认为大干沟岩体为早古生代造山后伸展阶段的产物,是东昆南地体与东昆北地体碰撞后地幔岩浆上涌及地壳熔融的结果。
The Dagangou granites in the Jinshuikou area of the East Kunlun orogen are mainly composed of medium-coarse grained syenogranites. Their SiO2 and Al2O3 values vary from 68.68% to 71.12% and 14.01% to 15.40%, with a mean value of 69.84% and 14.82%, respectively. The K2O/Na2O ratios are high （1.19～1.64, with a mean value of 1.40）. The A/CNK values[molar ratio of Al2O3/（CaO＋Na2O＋K2O）] are 0.98～1.02, with a mean value of 1.00, indicating the quasi aluminum-weakly peraluminous geochemical characteristics. All the Dagangou granites have high total REE abundances. Moreover, their chondrite-normalized REE patterns all show enrichment of LREE and obviously negative Eu anomalies. On the primitive mantle-normalized trace element diagrams, the samples have similar distribution patterns with enrichment of U, Th, and depletion of HFSEs （Ti, P, Nb, Ta） and Ba, Sr, indicating the geochemical characteristics of A-type granite. The εNd（t） values of -5.6～-7.3 and tDM values from 1.54 Ga to 2.27 Ga suggest that the source might have mainly been derived Proterozoic materials （Jinshuikou Group）. Zircon εHf（t）=2.2～2.6, significantly different from the earth＇s crust magmatic Hf isotopic compositions, showing that rocks were contaminated by the mantle. The LA-ICP-MS zircon U-Pb indicates that the granites were emplaced at 392±2 Ma （MSWD=1.14）. The geochemical characteristics combined with the tectonic evolution of East Kunlun show a pronounced affinity of post-orogenic granites, belonging to the response to the mantle magma upwelling and melting of the crust.
出处
《岩石矿物学杂志》
CAS
CSCD
北大核心
2016年第3期371-390,共20页
Acta Petrologica et Mineralogica
基金
中国地质调查局资助项目(1212011120158,12120114080101,12120115027001)~~
关键词
东昆仑
花岗岩
造山后
原特提斯
East Kunlun
granite
post-orogenic
proto-Tethys
