辽宁永甸地区辽吉花岗岩成因及对辽吉活动带构造演化的制约

Petrogenesis of Liaoji granites in Yongdian area of Liaoning and their constraints on tectonic evolution of Liao-Ji mobile belt

对永甸地区的辽吉花岗岩进行年代学和地球化学分析。锆石U-Pb定年结果表明,永甸花岗岩形成于(2 180.4±5.3)Ma。永甸花岗岩富Si(SiO_2=72.20%~73.54%),富碱(K_2O+Na_2O=7.83%~8.35%),贫Ca、Mg、Al(CaO=0.28%~1.37%,MgO=0.07%~0.14%,Al_2O_3=12.22%~12.88%)。稀土配分模式曲线为右倾型,有较强的负Eu异常(Eu/Eu*=0.38~0.69)和较高的Ga/Al比值,而且岩体富集Zr、U、Y等高场强元素以及Rb、K等大离子亲石元素,贫Ba、Sr等元素,这些特征表明永甸花岗岩属于A_2型花岗岩。根据岩石地球化学特征,认为永甸花岗岩形成于弧后盆地环境,来源于减薄下地壳岩石的部分熔融。

Zircon U-Pb chronological and geochemical research has been undertaken on the Liaoji granites in Yongdian area. LA-ICP-MS U-Pb zircon dating gives the emplacement age of 2 180. 4 ± 5. 3 Ma for Yongdian granites. Yongdian granites are characterized by high concentrations of silica( SiO_2= 72. 20% ~ 73. 54%) and total alkalis( K_2O + Na_2O = 7. 83% ~ 8. 35%),but low concentrations of Ca( CaO = 0. 28% ~ 1. 37%),Mg( MgO= 0. 07% ~ 0. 14%) and Al( Al_2O_3= 12. 22% ~ 12. 88%). The chondrite-normalized REE patterns show rightdipping linear trends with slightly negative Eu anomalies( Eu/Eu*= 0. 38 ~ 0. 69) and high Ga/Al ratios. Moreover,they are rich in HFSEs( e. g. Zr,U,and Y) and LILEs( e. g. Rb,K),and depleted in Nb,P,Ti and Sr,which suggest that Yongdian granites belong to A_2-type granite. Petrologic geochemistry indicate that Yongdian granites formed in back arc basin,mainly sourced from thinned lower crust.