SHRIMP zircon U-Pb dating and petrogeochemistry of Ordovician granite bodies in the southern segment of Gaoligong Mountain, western Yunnan Province

SHRIMP U-Pb dating of zircons from two representative samples of the batholith shows that the crystallization age is 473.5±2.9Ma and 461.5±7.3Ma respectively. Petrochemical and geochemical analyses show that the granite is high-silica (SiO2=71.06%-73.88%), high-aluminous (Al2O3=13.03%-14.27%), high-K (K2O=2.81%-5.53%), low-Ca (CaO=0.67%-1.71%) and peraluminous (ASI=1.4-1.8). There is an evident negative Eu anomaly(δEu=0.19-0.47) in its REE patterns. In the diagrams of trace element patterns, there are very high peaks of Rb and Th and strong depletion of Ba. As for the Sm and Nd isotopes, 143Nd/144Nd ratio is 0.512022 and 0.512056 respectively. The above data show that the magma of the granite was derived mainly from the melting of the upper crust. The authors have come to the conclusion that the emplacement and crystallization of the granite batholith had a close relationship with the collisional orogeny and crustal thickening and were also closely related to the crustal partial melting in the late period of the Pan-African orogeny.