Does Ocean Water Reach Mantle Plume Sources? If So What Are The Consequences?

Abstract

Plume basalts contain H_2O and CO_2, with possible sources: (1) the primordial Earth, (2) subducted lithosphere in deep mantle storage, or (3) the lithosphere. The depth at which volatile components dissolve in melt in a rising plume has consequences for trace element distributions. The subduction of volatile components from the hydrosphere is a distinctive feature of convergent plate boundaries. These components are contained in the sediments and altered basalt and gabbro and serpentinites of the oceanic crust, and in hydrated peridotite of the subducted lithosphere or overlying mantle wedge. Large volumes of volatile components are removed by underplating of sediments at the accretionary prism, and by diagenetic and low grade metamorphic reactions. Rocks of blueschist or greenschist facies are carried deeper, and they experience a series of progressive metamorphic reactions, with facies inverted because of the thermal structure.