Geochemical characteristics, rock-forming processes and tectonic setting of Late Paleozoic granites in the Songshishan area, Central Kunlun Mountains

Abstract：The Late Paleozoic granites occurring in the Songshishan area, Central Kunlun Mountains are composed of quartz diorite, tonalite, granodiorite and monzogranite. The rocks have low contents of SiO2 (56.42%-73.70%) and K2O (1.70%-3.56%) and are poor in alkalis with Na2O+K2O=6.13% on average and rich in sodium with Na2O=3.49% on average and K2O/Na2O= 0.51-0.99 and aluminium with Al2O3=14.90% on average. The granites as a whole are of magnesian, sub-aluminous-weakly peraluminous calc-calc-alkaline series. Ba, U, Nb, Ta, Sr, P and Ti are pronounced but not strongly depleted, while Rb, Th, K, La, Nd, (Zr+Hf+Sm) and (Y+Yb) are comparatively concentrated. ΣREE values average 105μg/g and LREE values are enriched with (La/Yb)N=13.91 on average. δEu values are weakly depleted or show no depletion, with δEu=0.85 on average. Quartz diorite is notably deviated from the evolution line in the Harker diagram of main oxides and has the lowest δEu values, monzogranite has the highest δEu values, the data points of the rocks fall in different fields of the C/MF-A/MF diagram, the oxide variation curves neither show straight lines nor form hyperbolas on the syn-denominator diagrams, the 4 types of granites do not show the trend of differentiation in the La/Sm-La diagram, and there are mafic microgranular enclaves of magma mingling origin in granites—all these suggest that the parent rocks and magma of the granites have multiple sources and that magma mixing occurred during the formation of the magma. The characteristics of the trace element spidergram, various oxide and trace element diagrams for tectonic environment discrimination and regional tectonic framework reveal that the rocks were formed in an island-arc environment.