Elemental budget and rheology of the oceanic lithosphere

Abstract

The compositions of the uppermost parts of subducting oceanic plates (sediments and altered crust) are relatively well known. However, the largest part of the downgoing slab, the lithospheric mantle (up to ∼10 times the thickness of the oceanic crust), is not well defined. By virtue of its size and refractory nature, this may be the subducted material with the longest lifespan within the convecting mantle; also, ancient recycled lithosphere may be a source reservoir to modern ocean island volcanism. We present results constraining the chemical compositions of the entirety of subducting tectonic plates, and discuss consequences of variations in lithospheric composition (especially water) for the rheology of subducted plates.