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Top-driven asymmetric mantle convection

By
Carlo Doglioni
Carlo Doglioni
Dipartimento di Scienze della Terra, Sapienza Università di Roma, Piazzale Aldo Moro 5, 00185 Rome, Italy
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Don L. Anderson
Don L. Anderson
Seismological Laboratory, California Institute of Technology, MS 252-21, Pasadena, California 91125, USA
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Published:
October 01, 2015

The role of decoupling in the low-velocity zone is crucial for understanding plate tectonics and mantle convection. Mantle convection models fail to integrate plate kinematics and thermodynamics of the mantle. In a first gross estimate, we computed at >300 km3/yr the volume of the plates lost along subduction zones. Mass balance predicts that slabs are compensated by broad passive upwellings beneath oceans and continents, passively emerging at oceanic ridges and backarc basins. These may correspond to the broad low-wavespeed regions found in the upper mantle by tomography. However, west-directed slabs enter the mantle more than three times faster (~232 km3/yr) than in the opposite east- or northeast-directed subduction zones (~74 km3/yr). This difference is consistent with the westward drift of the outer shell relative to the underlying mantle, which accounts for the steep dip of west-directed slabs, the asymmetry between flanks of oceanic ridges, and the directions of ridge migration. The larger recycling volumes along west-directed subduction zones imply asymmetric cooling of the underlying mantle and that there is an “easterly” directed component of the upwelling replacement mantle. In this model, mantle convection is tuned by polarized decoupling of the advecting and shearing upper boundary layer. Return mantle flow can result from passive volume balance rather than only by thermal buoyancy-driven upwelling.

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GSA Special Papers

The Interdisciplinary Earth: A Volume in Honor of Don L. Anderson

Gillian R. Foulger
Gillian R. Foulger
Department of Earth Sciences, Durham University, Durham DH1 3LE, UK
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Michele Lustrino
Michele Lustrino
Dipartimento di Scienze della Terra, Universita` degli Studi di Roma La Sapienza, P.le A. Moro, 5, 00185 Roma, Italy
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Scott D. King
Scott D. King
Department of Geosciences, Virginia Tech, Blacksburg, Virginia 24061, USA
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Geological Society of America
Volume
514
ISBN print:
9780813725147
Publication date:
October 01, 2015

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