title: Experimental evidence supports mantle partial melting in the asthenosphere.
abstract: The low-velocity zone (LVZ) is a persistent seismic feature in a broad range of geological contexts. It coincides in depth with the asthenosphere, a mantle region of lowered viscosity that may be essential to enabling plate motions. The LVZ has been proposed to originate from either partial melting or a change in the rheological properties of solid mantle minerals. The two scenarios imply drastically distinct physical and geochemical states, leading to fundamentally different conclusions on the dynamics of plate tectonics. We report in situ ultrasonic velocity measurements on a series of partially molten samples, composed of mixtures of olivine plus 0.1 to 4.0 volume % of basalt, under conditions relevant to the LVZ. Our measurements provide direct compressional (V P) and shear (V S) wave velocities and constrain attenuation as a function of melt fraction. Mantle partial melting appears to be a viable origin for the LVZ, for melt fractions as low as ~0.2%. In contrast, the presence of volatile elements appears necessary to explaining the extremely high V P/V S values observed in some local areas. The presence of melt in LVZ could play a major role in the dynamics of plate tectonics, favoring the decoupling of the plate relative to the asthenosphere.
authors.affiliation: Laboratoire Magmas et Volcans, CNRS UMR 6524, Université Blaise Pascal, Institut de Recherche pour le Developpement, 63178 Clermont-Ferrand, France.
authors.forename: Julien
authors.initials: J
authors.lastname: Chantel
authors.affiliation: Laboratoire Magmas et Volcans, CNRS UMR 6524, Université Blaise Pascal, Institut de Recherche pour le Developpement, 63178 Clermont-Ferrand, France.
authors.forename: Geeth
authors.initials: G
authors.lastname: Manthilake
authors.affiliation: Laboratoire Magmas et Volcans, CNRS UMR 6524, Université Blaise Pascal, Institut de Recherche pour le Developpement, 63178 Clermont-Ferrand, France.
authors.forename: Denis
authors.identifier: 0000-0002-9921-4572
authors.initials: D
authors.lastname: Andrault
authors.affiliation: Laboratoire Magmas et Volcans, CNRS UMR 6524, Université Blaise Pascal, Institut de Recherche pour le Developpement, 63178 Clermont-Ferrand, France.
authors.forename: Davide
authors.initials: D
authors.lastname: Novella
authors.affiliation: Center for Advanced Radiation Source, University of Chicago, Chicago, IL 60637, USA.
authors.forename: Tony
authors.identifier: 0000-0001-8283-2780
authors.initials: T
authors.lastname: Yu
authors.affiliation: Center for Advanced Radiation Source, University of Chicago, Chicago, IL 60637, USA.
authors.forename: Yanbin
authors.identifier: 0000-0001-5716-3183
authors.initials: Y
authors.lastname: Wang
mesh_terms: D019015:Geologic Sediments; D005844:Geology; D008962:Models, Theoretical
keywords: Partial melting; asthenosphere; attenuation; dynamics of plate tectonics; high pressure, high temperature; in situ ultrasonic velocity measurements; low velocity layer; multianvil; sound wave velocities; synchrotron