Zircon SHRIMP geochronology and Nd-Pb isotopic characteristics of the meta-basalt in the central part of Tibetan Plateau’s Qiangtang region

A small-sized meta-basic rock system is discovered in Qilongwuru Gully of Central Qiangtang’s Shuanghu region and contains a meta-basalt and garnet-bearing plagioclase amphibolite. The zircon U/Pb age of this meta-basalt by SHRIMP analysis is 463.3±4.7 Ma, suggesting that this lava formed in the Middle Ordovician, and is consistent with that of the meta-basic rocks in the Taoxing Lake and Guoganjianian Mountain ophiolite found in the Qiangtang plate. As this lava system bears similar geochemistry to N-MORB, it might be a component of ophiolite that represents the trail of the extinction of the Proto-Tethys, suggesting that the formation of Proto-Tethys oceanic basin in the Longmu Co-Shuanghu suture zone could date as far back as to the Middle Ordovician. Isotopic geochemical analysis indicates that the magma source area consists of both depleted mantle (DM) and enriched mantle (EMII) end members and bears Dupal anomaly, similar to that of the Paleo-Tethys in the Neo-Tethys represented by the Yarlung-Tsangpo suture zone, the Paleo-Tethys represented by the Changning-Menglian suture zone, and the Paleo-Tethys in Sanjiang region. This suggests that they have inherited the attribute of the Proto-Tethys mantle domain, and the Longmu Co-Shuanghu suture zone may be a representative of the northern boundary of Gondwana.