Origin of Carboniferous intra-oceanic arc granitoids from the eastern Pamir and implications for the Paleo-Tethyan ocean

The expanding and diminishing of the Paleo-Tethyan ocean recorded in the Pamir, and relationships between different segments of the Paleo-Tethyan suture from Pamir to Tibet are poorly constrained. Here we present new zircon U-Pb ages and geochemical data of the Waqia granitoid pluton from the eastern Pamir. Both the host granitoids and gabbroic to dioritic enclaves have similar zircon U-Pb ages of 323-318 Ma, being contempora-neous in origin. These rocks are metaluminous, calc-alkaline, tholeiitic series. They exhibit low K2O, low Sr/Y ratios, low REE contents with depleted to flat LREE patterns, slight enrichment in Rb, Ba, Zr, Hf, and negative Nb, Ta, P, and Ti anomalies. They have similar initial Sr-87/Sr-86 ratios of 0.7040 to 0.7045, positive epsilon(Nd)(t) (+4.63 to +5.02) and epsilon(Hf)(t) (+9.9 to +14.7) values. Detailed elemental and isotopic data indicate that these coeval rocks in the Waqia pluton were cognate and formed by hydrous partial melting of a juvenile mafic crust within an intraoceanic arc setting. This study is the first to report reliable isotopic ages of the early Paleo-Tethyan subduction in the eastern Pamir. Further, the Tanymas-Mazha Paleo-Tethyan suture in the eastern Pamir should be the western extension of the Jinshanjiang Paleo-Tethyan suture in the central to eastern Tibetan plateau. An integration of published results leads us to conclude that closure of the Jinshanjiang Paleo-Tethyan ocean was diachronous along its 3000-4000 km length, with closure times of ca 240 Ma in the Pamir and ca 220 Ma in the Sanjiang region.