LA-ICP-MS zircon U-Pb age and geological characteristics of the Early Jurassic potassium porphyritic granites in Kargang area, eastern Tibet

In this paper, LA-ICP-MS zircon U-Pb age test was carried out on the potassium porphyritic granites in the Kargang area, which shows that the ²⁰⁶Pb/²³⁸U age weighted average value of the rock mass is 178±2 Ma(MSWD=3.7, n=20), suggesting a product of Early Jurassic.The geochemical characteristics of the rocks show that the rocks have alkali-rich potassium(K₂O+Na₂O=8.02%~8.76%, K₂O/Na₂O=1.71~2.11), but low aluminum(Al₂O₃=14.08%~14.73%, A/CNK=1.01~1.04), without pyroxene and with lower corundum molecules.The rocks are generally characterized by rich Rb, Th, K, U and other large ionic pro-stone elements, obvious loss of Ba, Nb, Sr, P, Ti and other elements, and very low values of high field strength elements Zr, Nb, with(Ga/Al)×10⁴ values of 4.48~5.06 and Rb/Sr ratios of 1.84~2.29, which shows the characteristics of high magma differentiation; in addition, the formation of rocks was related to subduction reduction, and its tectonic environment changed gradually from extrusion environment to relative stretching environment, accompanied by the decrease of deep crustal pressure, which led to the upwelling of mantle source magma and the partial melting of the overlying crust.