Identification of the Puxia oceanic island in the southern margin of the Gangdise belt, and its geological significances

The Puxia oceanic island, located at the Changguo area, Gongga, Tibet,is a newly identified late Triassic oceanic island from the previous Sangri Group by the authors of this paper. By carrying out detailed geological survey and studies on rock associations, rock fabrics, rock geochemistry and zircon U-Pb dating, the authors believe that the Puxia oceanic island sequences, which are mainly composed of interbed basalt and limestone rocks, occurred in an oceanic island tectonic setting in the late Triassic. Our studies indicate that the studied area already occurred the mature oceanic crust as early as the late the late Triassic, according to our zircon U-Pb dating ages of 203.9 ±1.6Ma and 219.5 ±2.0Ma obtained from the basalts of the Puxiao ceanic island sequences.The Puxiao ceanic island sequences were formed by the northward subduction of the new Tethys Ocean to the Lhasa block.Identification of the late Triassic Puxia oceanic island has important and positive significances on studies of the geological evolution of the Gangdise belt and the new Tethys Ocean.