东昆仑和尔格头地区中三叠世和尔格头序列侵入岩地球化学特征及构造意义

Geochemical Characteristics and Tectonic Significance of the Intrusive Rocks from Middle Triassic Heergetou Sequence in Heergetou Area,East Kunlun

东昆仑和尔格头地区中三叠世侵入岩由石英闪长岩、花岗闪长岩、二长花岗岩组成,通过岩相学、主量元素、微量元素地球化学化学特征研究,岩体具有富硅(w(SiO2)为63.82%~72.68%)、富钾(w(K_2O)为3.55%~4.86%)、富碱[w(Na_2O+K_2O)为6.67%~8.23%]的特征。岩石里特曼指数δ=2.109~2.714,属钙碱性系列;铝饱和指数(A/CNK)=0.94~1.03,属准铝质-弱过铝质岩石。岩石稀土总量略低(ΣREE为145.90×10^(-6)~238.35×10^(-6)),富集轻稀土元素(LREE/HREE为8.11~13.23),轻稀土元素之间分馏明显(La_N/Yb_N为9.12~16.49)和中等负Eu异常(δEu=0.41~0.72)。微量元素蛛网图显示Rb具有明显富集,K、Th含量较高,Ba相对亏损,Ce、Hf、Zr、Sm、Y、Yb等明显低于洋脊花岗岩。以上特征表明,岩石属于高钾钙碱性S型花岗岩,具有火山弧花岗岩特征,是俯冲阶段地壳物质部分熔融的产物。

The middle Triassic intrusive rocks from Heergetou area in East Kunlun consist of quartz diorite, granodiorite and monzogranite. Based on the study of lithological and geochemistry characteristics of major elements and trace elements, the results show that these rocks are characterized by SiO2-rich （63.82%~72.68%）, K-rich （3.55%~4.86%） and alkali-rich （6.67%~8.23%）. Their rock Rittmann indexes （δ） range from 2.109 to 2.714, with the characteristic of calc-alkaline series, while their aluminum saturation indexes （A/CNK） vary from 0.94 to 1.03, with the characteristics of metaluminous or weakly peraluminous rocks. Geochemical analysis reveals that their REE is slightly lower （ΣREE is 145.90×10-6~238.35×10-6）, and they are enriched in LREE （LREE/HREE ratios are 8.11~13.23）, with obvious fractionation of LREE/HREE （LaN/YbN is 9.12~16.49） and moderate negative Eu anomaly （δEu is 0.41~0.72）. Spider diagrams of trace elements displays a significant positive Rb-anomaly, a slight negative Ba-anomaly, the enrichments of K and Th, while the values of Ce,Hf,Zr,Sm,Y,Yb are lower than the ridge granitoids obviously. Petrology and elemental geochemistry suggest that the middle Triassic intrusive rocks belong to the high K, cal-alkaline S-type granite and have the characteristics of volcanic arc granite, which is the product of the melting of the crust material in the subduction stage.