The granulites and ages of the Nyingchi Group Complex in the Nyingchi region,Xizang

The Nyingchi Group Complex assigned to the basement series of the Gangdise magmatic arc crops out along the valleys of the Nyang and Yarlung Zangbo Rivers on the western side of the Yarlung Zangbo Grand Canyon in the Nyingchi region, Xizang. During the geological survey in recent years,the granulites are identified as lenses, cakes, nodules and pods in places in the intermediate-to high-grade metamorphic basic rocks in the lower part of the Nyingchi Group Complex in Nailung on the eastern bank and Zhaxiraodeng on the western bank of the Yarlung Zangbo River.The granulites are characterized by higher MgO and CaO contents, lower TiO₂ and K₂O contents,and Al₂O₃/ TiO₂ ratios of nearly 20, similar to those of representative basaltic komatiite in other places of the world.The lower rare earth element amounts show the similarity to the intermediate-basic volcanic rocks. Their prolioths may be represented by Mg-rich ultramafic and mafic volcanic rocks which are traced back to the Palaeoproterozoic.