Slab

About: Slab is a research topic. Over the lifetime, 31617 publications have been published within this topic receiving 318693 citations.

Kinematics of subduction and subduction-induced flow in the upper mantle

Abstract: [1] Results of fluid dynamical experiments are presented to model the kinematics of lithospheric subduction in the upper mantle. The experiments model a dense high-viscosity plate (subducting lithosphere) overlying a less dense low-viscosity layer (upper mantle). The overriding lithosphere is not incorporated. Several important features of slab behavior were investigated including the temporal variability of hinge line migration, the kinematic behavior of the slab and the subduction-induced upper mantle flow. Both fixed and free trailing edge boundary conditions of the subducting plate were investigated. Results show that hinge line retreat is a natural consequence of subduction of a negatively buoyant slab. The migration rate increases until the slab approaches the upper-lower mantle discontinuity, resulting in a decrease in migration rate followed by a renewed increase and finally approaching a steady state. Slab retreat results in mantle flow, with material initially located underneath the slab flowing around the lateral slab edges toward the mantle wedge. Experimental results indicate that all rollback-induced flow occurs around the lateral slab edges, forcing the hinge line to attain a convex shape toward the direction of retreat. No signs for poloidal flow underneath the slab tip have been detected. Only a small component of toroidal-type flow was observed underneath slanting slab tips. For a fixed trailing edge, the slab does not sink vertically downward, but sinks at an angle in a regressive manner. For a free trailing edge, slab sinking is oriented more vertically while the surface part of the subducting plate is pulled into the subduction zone.

Fluid influence on the trace element compositions of subduction zone magmas

Abstract: Subduction zones represent major sites of chemical fractionation within the Earth. Element pairs which behave coherently during normal mantle melting may become strongly decoupled from one another during the slab dehydration processes and during hydrous melting conditions in the slab and in the mantle wedge. This results in the large ion lithophile elements (e.g. K, Rb, Th, U, Ba) and the light rare earth elements being transferred from the slab to the mantle wedge, and being concentrated within the mantle wedge by hydrous fluids, stabilized in hydrous phases such as hornblende and phlogopite, from where they are eventually extracted as magmas and contribute to growth of the continental crust. High-field strength elements (e.g. Nb, Ta, Ti, P, Zr) are insoluble in hydrous fluids and relatively insoluble in hydrous melts, and remain in the subducted slab and the adjacent parts of the mantle which are dragged down and contribute to the source for ocean island basalts. The required element fractionations result from interaction between specific mineral phases (hornblende, phlogopite, rutile, sphene, etc.) and hydrous fluids. In present day subduction magmatism the mantle wedge contributes dominantly to the chemical budget, and there is a requirement for significant convection to maintain the element flux. In the Precambrian, melting of subducted ocean crust may have been easier, providing an enhanced slab contribution to continental growth.