The energetics of melting fertile heterogeneities within the depleted mantle

Katz, R. F. and Rudge, John F. (2011) The energetics of melting fertile heterogeneities within the depleted mantle. Geochemistry Geophysics Geosystems, 12. ISSN ESSN: 1525-2027 DOI 10.1029/2011GC003834

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Abstract

To explore the consequences of mantle heterogeneity for primary melt production, we develop a mathematical model of energy conservation for an upwelling, melting body of recycled oceanic crust embedded in the depleted upper mantle. We consider the end‐member geometric cases of spherical blobs and tabular veins. The model predicts that thermal diffusion into the heterogeneity can cause a factor‐of‐ two increase in the degree of melting for bodies with minimum dimension smaller than ∼1 km, yielding melt fractions between 50 and 80%. The role of diffusion is quantified by an appropriately defined Peclet number, which represents the balance of diffusion‐driven and adiabatic melting. At intermediate Peclet number, we show that melting a heterogeneity can cool the ambient mantle by up to ∼20 K (spherical) or ∼60 K (tabular) within a distance of two times the characteristic size of the body. At small Peclet number, where heterogeneities are expected to be in thermal equilibrium with the ambient mantle, we calculate the energetic effect of pyroxenite melting on the surrounding peridotite; we find that each 5% of recycled oceanic crust diminishes the peridotite degree of melting by 1–2%. Injection of the magma from highly molten bodies of recycled oceanic crust into a melting region of depleted upper mantle may nucleate reactive‐dissolution channels that remain chemically isolated from the surrounding peridotite.

Item Type: Article
Additional Information: Copyright 2011 by the American Geophysical Union.
Subjects: 02 - Geodynamics, Geophysics and Tectonics
Divisions: 02 - Geodynamics, Geophysics and Tectonics
Journal or Publication Title: Geochemistry Geophysics Geosystems
Volume: 12
Identification Number: 10.1029/2011GC003834
Depositing User: Sarah Humbert
Date Deposited: 11 Apr 2013 10:49
Last Modified: 11 Jul 2014 11:42
URI: http://eprints.esc.cam.ac.uk/id/eprint/2743

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