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

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 (La_N/Yb_N 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.