Geochronological and geochemical characteristics of rhyolite in the Manketou'ebo Formation of Dong Ujimqin Banner, Inner Mongolia, and its geological implications

In order to determine the age attribution and tectonic setting of the volcanic strata of the Manketou'ebo Formation in Dong Ujimqin Banner of Inner Mongolia, the authors studied the geochronological and geochemical characteristics of the rhyolite from the Manketou'ebo Formation. The weighted age of rhyolite by LA-ICP-MS zircon U-Pb dating is 150.9±4.2Ma, suggesting Late Jurassic. The rhyolite in the Manketou'ebo Formation belongs to the high-potassic calc-alkaline series of rocks and is characterized by high silicon, rich alkali, high aluminum, low calcium and depleted magnesium. The total amount of rare earth elements changes greatly, the distribution curve is right-inclined, and there is negative anomaly of Eu. The rocks are enriched in large ion lithophile elements of Rb, K, Th, and LREE, and simultaneously depleted in elements of Sr, Nb, Ti and P. The basic compatible elements Cr, Co, Ni and Mg^# are relatively low, and the magma was derived from the partial melting of the lower crust rocks. According to element geochemical characteristics, rhyolite has A-type granite characteristics. Combined with the related structural discriminant diagrams, the authors hold that the Dong Ujimqin Banner area was in an extensional tectonic setting in the Late Jurassic, and may be related to the extensional system of the Mongolian-Okhotsk Ocean after the closure of the ocean.