西藏比如盆地竟柱山组沉积-火山岩形成环境及构造意义

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

上白垩统竟柱山组为一套冲积扇-扇三角洲沉积体系的粗碎屑岩,间夹由英安岩、安山岩、石英粗安岩和流纹岩组成的中酸性火山岩。火山岩呈层状、似层状产出,与碎屑岩均呈整合接触关系。地球化学特征表明,竟柱山组火山岩形成于岛弧构造环境,是挤压背景下地壳增厚熔融的产物。竟柱山组沉积-火山岩的形成环境揭示了比如盆地的性质在晚白垩世已由弧后盆地转换为前陆盆地。

The Upper Cretaceous J ingzhushan Formation in the Biru Basin, Xizang consists of a succession of coarse-grained elastic 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 elastic 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.