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The recycling of subcontinental lithospheric mantle back into the asthenosphere during continental breakup is potentially a major but underappreciated process in plate tectonics. Here, we report major and trace elements for detrital peridotite minerals in carbonate breccias dredged from the Marion Rise, Southwest Indian Ridge. With an emphasis on the trace elements of the relatively abundant orthopyroxene detrital grains, the results show that a portion of pyroxene grains was likely derived from a mantle source that experienced hydrous melting and slab‐derived melt metasomatism above a subduction zone. This finding provides a novel view into the mantle geochemistry at midocean ridges, as well as evidence that Marion Rise is at least partially supported by chemically buoyant recycled refractory mantle wedge material. [ABSTRACT FROM AUTHOR]

Lower crusts of oceanic plateaus have been rarely studied and their nature remains unclear, due to low probability in preservation. Here we demonstrate that cumulates of the Pengco Complex in central Tibet represent the lower crust of an oceanic plateau generated at ~188 Ma. Mineral crystallization order and geochemistry support their formation via low‐P fractionation from anhydrous basaltic melts. The Pengco cumulates are more magnesium rich and more depleted in rare earth elements than the mid‐ocean ridge cumulates, supporting a mantle source more refractory than the depleted MORB mantle (DMM). However, the extrusive rocks outcropped in the Pengco Complex are younger (161–166 Ma) and have a subducted‐related genesis. Such a temporal and genetical decoupling between the lower and upper crustal rocks in the Pengco Complex resulted from the subduction re‐initiation that was triggered by the oceanic plateau‐continent collision at ~164 Ma. [ABSTRACT FROM AUTHOR]