Late Paleozoic granitoids from central Qiangtang, northern Tibetan plateau: A record of Paleo-Tethys Ocean subduction

The Longmu Co-Shuanghu suture zone in central Qiangtang, northern Tibetan plateau, is a segment of the main suture zone of the Paleo-Tethys Ocean. Numerous studies have focused on ophiolite and high-pressure metamorphic rocks from this suture zone, whereas the associated subduction-related magmatic rocks have received little attention. In this study, we present new data for the Late Paleozoic granitoids from the Gangma Co, Guoganjianian and Chasum areas along the Longmu Co-Shuanghu suture zone. Zircon U-Pb dating indicates that these granitic rocks were emplaced between 364 Ma and 346 Ma (Late Devonian-Early Carboniferous). Three granitic plutons exhibit different geochemical compositions, but show uniform Sr-Nd and zircon Hf isotopic features with positive Ɛ_Nd(T) and zircon Ɛ_Hf(T) values. Furthermore, these rocks were all formed in a volcanic arc setting associated with an oceanic subduction zone. Together with data from coeval volcanic rocks, we suggest that the Late Paleozoic magmatic rocks were formed as a result of northward subduction of the Paleo-Tethys Ocean. Subduction of the Paleo-Tethys Ocean probably commenced in the Late Devonian, continued throughout the Late Paleozoic, and ended in the Triassic.