Zircon U-Pb age and geochemistry of Early Cretaceous rhyolite in Luozha area of Namling County, Tibet

Abstract：The authors studied the nearly EW-trending volcanic rocks in vast areas of northern Luozha zone along the Gangdise arc-ridge fault-uplift zone, obtained the LA-ICP-MS zircon age of 129.8±1.4 Ma, and proved for the first time the existence of Early Cretaceous volcanic rocks in the Gangdise arc-ridge fault-uplift zone. The volcanic rocks are characterized by high SiO2, K2O and K2O/Na2O values, the enrichment of LILEs (Rb, Ba, Th and U) and the depletion of Nb, Ta and Ti. Their cobweb curve is on the whole the same as that of the upper crust and the acidic volcanic rocks owing to crustal remelting of Zenong Group of the Gangdise zone at 110 Ma. These data indicate that the volcanic rocks might be the remelting products resulting from the dehydration of crustal materials. According to the environmental discrimination diagrams of trace elements, the authors consider that they are arc volcanic rocks. In combination with the tectonic background of Early Cretaceous period, it is thought that they were most likely associated with northward subduction of the Yarlung Zangbo River oceanic crust.