Geochronology and mineralization significance of the Late Cretaceous Xiaolonghe granite in the Tengchong Block

In order to determine the Late Cretaceous tectonomagmatic activities and the significance of granite mineralization in the Tengchong Block, this study applied the comprehensive methods of geochronology, Sr−Nd−Pb isotopic and whole−rock geochemical analyses to probe Xiaolonghe granites. The results show that the Xiaolonghe pluton is composed of fine−grained leuco−monzogranite and porphyritic−like biotite monzogranite. Zircon U−Pb chronological data indicate that their magmatic crystallization ages are 67.0±1.0 Ma and 68.5±1.6 Ma respectively, and the Re−Os model ages of molybdenite are 67.15±0.99 Ma and 69.02±1.22 Ma respectively, both of which are the products of the Late Cretaceous tectonomagmatic activities. The characteristics of Sr−Nd−Pb isotopes and major and trace elements show that the fine−grained leuco−monzogranite is S−type granite ((⁸⁷Sr/⁸⁶Sr)_i=0.757 ~ 0.763, ε_Nd(t)=−8.89 ~ −8.99), and the magma originated from the partial melting of clay−rich hard sandstone in the upper crust of Mesoproterozoic(T_DM2=1.59 ~ 1.60 Ga), which is closely−related to the formation of Xiaolonghe tin−tungsten polymetallic deposit. The porphyritic−like biotite monzogranite is I−type granite ((⁸⁷Sr/⁸⁶Sr)_i=0.711, ε_Nd(t)=−8.72 ~ −9.16), and the magma originated from the remelting of clay−rich hard sandstone in the lower crust of Mesoproterozoic(T_DM2=1.58 ~ 1.62 Ga). The Late Cretaceous Xiaolonghe granites and its tin−tungsten mineralization in the Tengchong Block are the products of magmatic activity and hydrothermal process caused by the collision or post−collision between the Tengchong Block and the Baoshan Block after the closure of the Meso−Tethys Bangong−Nujiang ocean.