The birth of the Ganzi-Litang embryonic ocean in the eastern Tibetan Plateau

The Tibetan Plateau is an assemblage of continental blocks rifted from Gondwana and accreted to Eurasia after the closure of several Tethyan oceanic branches. The Ganzi-Litang ocean, as an eastern branch of the Paleo-Tethys, has been subject to a long debate particularly regarding its opening time, nature, and relationship with the Emeishan mantle plume. Here we present detailed field investigation combined with petrographic, geochemical, and geochronological analyses on mafic and sedimentary rocks from the Ganzi-Litang mélange zone. The 281.9 ± 3.8 Ma cumulate gabbro and associated enriched mid-oceanic-ridge-type basalts in the Ganzi ophiolitic complex indicate the Ganzi-Litang ocean initially formed in the Early Permian. Then the Middle−Late Permian Emeishan plume generated seamounts in the Ganzi-Litang ocean, as recorded by newly identified ocean-island basalt (261−254 Ma) capped by radiolarian cherts in the Litang area. These mafic rocks are characterized by high TiO2 (3.1−4.2 wt%) and Ti/Y, with positive zircon εHf(t) of +5.0 to +10.3 and whole-rock εNd(t) of 0 to +1.0, closely matching the signature of high-Ti Emeishan basalts. The occurrence of continental margin-type cherts and of Emeishan basalts along the suture allow us to envisage the Ganzi-Litang embryonic ocean as part of the hyper-extended margin of the South China Block that underwent further extension related to the emplacement of the Emeishan plume. These findings not only shed new light on the paleogeographic evolution of the eastern Paleo-Tethys but also have important implications for the regional exploration of Emeishan plume-related Fe−Ti−V ore deposits.