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Thermal and chemical convection in planetary mantlesMelting of the upper mantle and extraction of melt result in the formation of a less dense depleted mantle. This paper describes series of two-dimensional models that investigate the effects of chemical buoyancy induced by these density variations. A tracer particles method has been set up to follow as closely as possible the chemical state of the mantle and to model the chemical buoyant force at each grid point. Each series of models provides the evolution with time of magma production, crustal thickness, surface heat flux, and thermal and chemical state of the mantle. First, models that do not take into account the displacement of plates at the surface of Earth demonstrate that chemical buoyancy has an important effect on the geometry of convection. Then models include horizontal motion of plates 5000 km wide. Recycling of crust is taken into account. For a sufficiently high plate velocity which depends on the thermal Rayleigh number, the cell's size is strongly coupled with the plate's size. Plate motion forces chemically buoyant material to sink into the mantle. Then the positive chemical buoyancy yields upwelling as depleted mantle reaches the interface between the upper and the lower mantle. This process is very efficient in mixing the depleted and undepleted mantle at the scale of the grid spacing since these zones of upwelling disrupt the large convective flow. At low spreading rates, zones of upwelling develop quickly, melting occurs, and the model predicts intraplate volcanism by melting of subducted crust. At fast spreading rates, depleted mantle also favors the formation of these zones of upwelling, but they are not strong enough to yield partial melting. Their rapid displacement toward the ridge contributes to faster large-scale homogenization.
Document ID
19950043363
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Dupeyrat, L.
(Universite de Paris Sud Paris, France)
Sotin, C.
(Universite de Paris Sud Paris, France)
Parmentier, E. M.
(Brown University Providence, RI, United States)
Date Acquired
August 16, 2013
Publication Date
January 10, 1995
Publication Information
Publication: Journal of Geophysical Research
Volume: 100
Issue: B1
ISSN: 0148-0227
Subject Category
Geophysics
Accession Number
95A74962
Funding Number(s)
CONTRACT_GRANT: NAGW-1928
Distribution Limits
Public
Copyright
Other

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