Tectonic setting and significance of the sedimentary-volcanic rocks from the Jingzhushan Formation in the Biru Basin,Xizang

The Upper Cretaceous Jingzhushan Formation in the Biru Basin,Xizang consists of a succession of coarse-grained clastic rocks in the alluvial fan-fan delta depositional system,intercalated with intermediate-acidic volcanic rocks including dacite,andesite,quartz trachyandesite and rhyolite.These volcanic rocks occur as stratified or stratoid beds,and are in conformable contact with the clastic rocks.The geochemical signatures show that the volcanic rocks in the Jingzhushan Formation were formed in the island-arc environment as crustal thickening-melting products in a compressional tectonic setting.The Biru Basin developed into a foreland basin during the Late Cretaceous.