Arc signatures in abyssal peridotites and its implications

Abstract

Investigating mass exchanges between the subduction zones and mid-ocean ridges provides essential clues to understanding recycling process and mantle convection in the Earth's mantle. In this study, we found evidence of recycled subduction signals in the abyssal peridotites from mid-ocean ridges through their extremely low bulk (Dy/Yb)N and bulk Al2O3, which could not be explained by normal decompression melting at mid-ocean ridges, but required a hydrous melting history. We show here that abyssal peridotites from the fast-spreading Pacific Oceanic Ridges (East-Pacific Rise and Pacific-Antarctic Ridge), to the ultraslow-spreading Southwest Indian Ridge and to the slow-spreading Mid-Atlantic Ridge, require increasing amount of slab-derived fluid in their mantle sources. Therefore, the subduction influence on abyssal peridotites is independent of the spreading rates of the overlying ridges. Locations, such as the Fifteen-Twenty Fracture Zone, the Rainbow Massif from the MAR and the Hess Deep from EPR, have abyssal peridotites overlap well with forearc peridotites, suggesting that the prominent characteristics of arc mantle wedge could be preserved in abyssal peridotites when the traveling distance or time is short for the recycled arc mantle migrating in the mantle convection flow. The well-preserved subduction-related signature in ridge areas that are relatively proximal to modern subduction zones imply that mass exchanges between the subduction zones and mid-ocean ridges may be more efficient than previously thought.