Petrology of Subducted Slabs

TLDR

Subducted lithosphere consists of complex chemical systems undergoing continuous and discontinuous phase transformations driven by pressure–temperature changes, with volatile recycling and minor, volatile‑bearing phases controlling buoyancy, petrogenesis, and devolatilization over more than 300 km of the slab–mantle interface. Density data at 660 km indicate that subducted slabs episodically penetrate the lower mantle and sink to the D″ region at the core–mantle boundary.

Abstract

▪ Abstract The subducted lithosphere is composed of a complex pattern of chemical systems that undergo continuous and discontinuous phase transformation, through pressure and temperature variations. Volatile recycling plays a major geodynamic role in triggering mass transfer, melting, and volcanism. Although buoyancy forces are controlled by modal amounts of the most abundant phases, usually volatile-free, petrogenesis and chemical differentiation are controlled by the occurrence of minor phases, most of them volatile-bearing. Devolatilization of the subducted lithosphere is a continuous process distributed over more than 300 km of the slab-mantle interface. Melting of the subducted crust, if any, along sufficiently hot P-T paths, is governed by fluid-absent reactions, even though the difference between fluid and melt vanishes at pressures above the second critical end point. The density distribution at a depth of 660 km suggests episodic penetration in space and time of subducted slabs into the lower mantle and sinking down to the D″ region at the core-mantle boundary.