PETROGEOCHEMISTRY AND GENESIS OF THE VOLCANIC ROCKS OF MANITU FORMATION IN TUQUAN BASIN, MIDDLE DAXINGANLING MOUNTAINS

The andesite of Manitu Formation in the Tuquan Basin, Eastern Inner Mongolia, is tectonically located in the middle section of Daxinganling tectonomagmatic belt, in the Late Mesozoic continental marginal accretion zone on the northern margin of North China Plate. Study of petrogeochemistry indicates that the andesite is characterized by high silica (with SiO₂ of 60.64%-64.36%) and alumina (Al₂O₃ 15.84%-17.38%), and medium alkali (Na₂O 3.76%-5.30%, K₂O 2.44%-3.81%), belonging to peraluminous high potassium calc-alkali rock. The chondrite standard curve of rare earth elements reveals an enrichment of LREE and deficit of HREE, without Eu and Ce anomaly. The andesite is enriched in LILE (such as Rb, K, Ba and LREE), mobile incompatible elements (such as U and Th), relatively depleted in HFSE (such as Nb, Ta, P and Ti) and HREE. The primitive magma of the andesite is derived from the partial melting of the crust, as the result of the closure of Mongolia-Okhotsk Ocean in the extensional environment of the lithosphere.