Timing and geochemistry of the Linzizong Group volcanic rocks in Sangsang area, Ngamring County, southern Tibet

The Linzizong Group volcanic rocks in Sangsang area consist mainly of high-K rhyolite formed at 49.85±0.92Ma (SHRIMP zircon U-Pb age), belonging to Pana Formation. They are characterized by (1) enrichment of LREE and depletion of HREE; (2) pronounced negative Eu anomalies; (3) relatively low initial Sr (87Sr/86Sr(i)=0.70488~0.70569) and high εNd values (εNd(i)=-1.38~-1.58); and (4) relative enrichment of LILEs and depletion of HFSEs, similar to things of arc-type volcanic rocks. These data indicate that fractional crystallization of amphibole as well as plagioclase played an important role in the formation of the Sangsang volcanic rocks. The Sangsang volcanic rocks might have been derived from melting of mature continental materials and a metasomatic lithospheric mantle source induced either by the roll-back or by the break-off of the subducted Neo-Tethyan slab. The data obtained by the authors, in combination with those from the literature, further demonstrate that the southern Gangdise belt must have experienced a large-scale magmatic event at approximately 50 Ma.