image: (a-b) Tectonic discrimination diagrams for picrite and basaltic rocks of the ophiolitic complexes from the Qilian-Qinling accretionary belt (QQAB). (c) Calculated melting conditions for primary magmas of the picrite-basalt sequence from the QQAB ophiolitic complexes. (d) Lu/Hf vs. La/Sm diagram for picrite and basaltic rocks from the QQAB ophiolitic complexes. The curves show the effect of between 0.01% and 20% equilibrium melting of spinel and garnet peridotite.
Credit: ©Science China Press
This study is led by Dr. Jinran Qiao (School of Earth and Space Sciences, Peking University), Prof. Shuguang Song (School of Earth and Space Sciences, Peking University), associate professor Jie Dong (School of Earth Sciences, Jilin University), Prof. Mark B. Allen (Department of Earth Sciences, Durham University) and associate professor Li Su (China University of Geosciences).
Mantle plumes from deep Earth’s interior play a significant role in mantle convection and plate tectonics. Their impact on oceanic lithosphere is invoked to initiate oceanic subduction and modern plate tectonics in the early Earth, and they may also contribute to the rifting and break-up of continents and follow oceanic spreading to form open ocean basins during the early stage of the Wilson cycle in the Phanerozoic.
The team have reported the existence of a series of plume-type ophiolite complexes with pillow/massive basaltic and picritic lavas from the Qilian-Qinling Accretionary Belt (QQAB) in Central China. These rocks exhibit typical enriched mid-ocean ridge basalt (E-MORB) and ocean island basalt (OIB) geochemical affinities with high mantle potential temperature (Tp) of ~1489–1583 °C, assuring their mantle plume origins.
Combing with zircon U-Pb dating for eleven gabbro and basalt samples and reported age data, they were mainly formed in the duration of 472–621 Ma, which indicating the operation of long-lived (~150 Myr) mantle plume activities. Such plume-related magmatism has recorded the onset and spreading of the Proto-Tethys Ocean from ~620 Ma to ~470 Ma, and the associated intraplate seamounts/plateaus provide a unique window for understanding the interplay between plume and oceanic lithosphere during the spreading of the oceanic crust.
Journal
Science Bulletin