Delineation of Middle Carboniferous Arc Volcanic Rocks in Jomda Area, Eastern Tibet and Its Tectonic Implications

The Jinshajiang Tethys is one of the most important ocean basins in the Sanjiang region.However, it is not clear when the oceanic subduction started.The research of arc volcanic rock is significant to constrain the subduction process of the oceanic plate.This paper reports the Late Middle Carboniferous volcanic rocks in Jomda area, eastern Tibet, which are dominated by basalts and andesites.Zircon U-Pb age results show they were formed at 332±3.3 Ma.The arc volcanic rocks have SiO 2 contents of 45.65%-55.73%, Al 2 O 3 contents of 15.48%-16.79%, TiO 2 contents of 0.82%-1.12%, and have high Na/K ratios.They show obvious differentiation between LREE and HREE, and without Eu anomaly.They are enriched in strong incompatible trace elements, such as Th and U, and depleted in high field strength element, such as Nb and Ta.The zircons from basalts have positive ε Hf (t) values(+11.0 to +15.6), which indicates that the magma source might be the enriched lithosphere mantle.It is believed that Late Middle Carboniferous volcanic rocks were formed at the island arc tectonic enviorment, which is related to subduction of Jinshajiang Tethys ocean.Combining with the regional geological data, we propose that the subduction of the Jinshajiang Tethys ocean have started before 332 Ma.This study provides a lithology evidence for the evolution of Jinshajiang Tethys ocean. © 2018, Editorial Department of Earth Science. All right reserved.