Petrogenesis, geochemistry and geological significance of Paleocene Granite in South Gangdese, Tibet

The Gangdese magmatic belt, located along the southern margin of the Lhasa terrane, plays a critical role in understanding the tectonic framework associated with the Indian–Asian slab collision. In this paper, a chronology of zircon U–Pb and geochemical analysis of the rock of the Cuobulaguo granitic mass in the southern of the Gangdese, Tibet, revealed a series of results. The results show that the LA-ICP-MS monzonitic granite zircon U–Pb ages are 61–59 Ma, which corresponds to the same period as the magmatic arc of the southern limit of Gangdese. In terms of geochemical composition, the granite is rich in ω(SiO 2 ) 70.09% to 72.64%, with a high ω(Al 2 O 3 ) 14.40% to 15.99%, a low ω(TiO 2 ) 0.08% to 0.24%, ω(MgO) 0.41% to 0.76%, ω(Fe 2 O 3 T ) 6.82% to 29.9%, ω(P 2 O 5 ) 0.07% to 0.12%, and ω(CaO) 1.06% to 1.75%. The granite mainly belongs to the high-K calc-alkaline series. The light rare earth element (LREE) content of skeletal granite is between 133.69 × 10 −6 ~ 226.64 × 10 −6 and the heavy rare earth element (HREE) content is between 17.36 × 10 −6 and 32.11 × 10 −6 . LREE/HREE is between 5.05 and 7.83. It is enriched in light rare earth elements (LREE) and large ion lithophile elements, such as Rb, K, U, etc., depletes high field strength elements, such as P, Nb, and Ta, and has the geochemical composition of arc magmatic rocks. In addition, the aluminum saturation index (A/CNK = 1.06 to 1.11) of Cuobulaguo granite, belongs to I-type granite. The comprehensive analysis showed that with the beginning of the collision between the Indian–Asian continental, the subduction ocean plate was separated from the continental plate due to gravity, resulting in an increase in the asthenosphere, which made partial fusion of the lithospheric mantle. It invaded the bottom of the lower crust, which in turn induced a partial melting of the lower crust to form granite.