Petrological, geochemical and geochronological features of Lailishan ganitoids in western Yunnan and their genesis of partial melting of crustal soure

Granites genetically related to tin ore deposits always constitute the focus of geological studies. The Lailishan granitoids are located in the Tengchong-Lianghe area of western Yunnan and belong tectonically to Tengliang granitoids. These granites extend in NNE direction as a belt, connected with Gangdise belt on the north. The Lailishan granitoids are mainly composed of porphyaceous biotite monzogranite and medium to coarse-grained biotite syenogranite. Based on the data available, the authors conducted petrological, geochemical and geochronological studies of the Lailisahn granitoids. The zircon LA-ICP-MS U-Pb age of the monzogranite (14L-4) is 52.34 ±0.68Ma (MSWD=1.4, n=26). Geochemically, the monzogranite is relatively rich in Al (Al₂O₃=14.70%-15.27%), alkalis (K₂O+Na₂O=8.07%-8.50%), Ca (CaO=1.64%-2.56%), REE, and Ba. The ASI values range from 0.97 to 1.12, 1.04 on average, indicating that monzogranite is from metaluminous to weakly peraluminous. The syenogranite is relatively rich in Si (SiO₂=74.57%-76.69%) and Rb, and strongly depleted in Ba, Sr, P, Ti, and Eu. The ASI values range from 1.05 to 1.18, 1.09 on average, indicating weakly peraluminous features. The monzogranite and syenogranite originated from the same magma reservoir but emplaced at different stages; the evolution of them in mineralogy, geochemistry and chronology was obvious, suggesting S-type granites. It is therefore held that the Lailishan granitoids originated from crust partial melting in deep crust during main Indian-Euro-Asian collision period, responding to the interaction between the Indian-Euro-Asian continents.