The discovery and significance of the rapakivi granites in Gyisong,Tangra Yumco,Xizang

The rapakivi granites were discovered during the 1:25 000 regional geological survey in Gyisong, Tangra Yumco, Xizang. These granites give a K-Ar age of 45.3 Ma and may be traced back to the Eocene. They are characterized by special oval rapakivi textures, higher K₂O +Na₂O contents, K₂O >Na₂O, higher REE contents and depletion of the element Eu, and thus belong to the orogenic rapakivi granites originated from the intracontinental post-collisional settings during the later stages of collision and mountain building of the Qinghai-Xizang Plateau.