Picrite-basalt complex in the Baoshan-Gongshan Block of northern Sibumasu: Onset of a mantle plume before breakup of Gondwana and opening of the Neo-Tethys Ocean

Mantle plumes are thought to play key roles in Earth's geodynamics, including mantle convection, continental formation, and plate tectonics. The connection between plume activity and continental dispersion, as exemplified by the breakup of Gond-wana and the generation of the Neo-Tethys Ocean, is a key question for the geosciences. Here, we present detailed investigations for the picrite-basalt sequence in the Baoshan-Gongshan Block of the northern Sibumasu terrane, southwest China. Field relations and petrological and geochemical data reveal that these volcanic rocks are continental flood picrites and basalts, consistent with a mantle plume origin. The estimated mantle potential temperatures range from 1527 +/- 86 degrees C to 1546 +/- 98 degrees C, and melting depths vary from the spinel to garnet stability fields (1.1-5.3 GPa), similar to Cenozoic Hawaiian picrites. Zircon geochronological data show that the mantle plume activity started at ca. 335 Ma and lasted to 280 Ma; this range is earlier than the breakup of the Gondwana continent and opening of the Neo-Tethys Ocean (270-260 Ma). We conclude that the long-lived mantle plume impacted the continental lithosphere but it did not drive continental breakup and the opening of Neo-Tethys Ocean, which took place because of the subduction-induced stress generated by initial subduction of the Paleo-Tethys Ocean.