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Slabs in the lower mantle and their modulation of plume formation

Tan, Eh and Gurnis, Michael and Han, Lijie (2002) Slabs in the lower mantle and their modulation of plume formation. Geochemistry, Geophysics, Geosystems, 3 (11). 2001GC000238. ISSN 1525-2027. http://resolver.caltech.edu/CaltechAUTHORS:TANggg02

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Abstract

Numerical mantle convection models indicate that subducting slabs can reach the core-mantle boundary (CMB) for a wide range of assumed material properties and plate tectonic histories. An increase in lower mantle viscosity, a phase transition at 660 km depth, depth-dependent thermal expansivity, and depth-dependent thermal diffusivity do not preclude model slabs from reaching the CMB. We find that ancient slabs could be associated with lateral temperature anomalies ~500°C cooler than ambient mantle. Plausible increases of thermal conductivity with depth will not cause slabs to diffuse away. Regional spherical models with actual plate evolutionary models show that slabs are unlikely to be continuous from the upper mantle to the CMB, even for radially simple mantle structures. The observation from tomography showing only a few continuous slab-like features from the surface to the CMB may be a result of complex plate kinematics, not mantle layering. There are important consequences of deeply penetrating slabs. Our models show that plumes preferentially develop on the edge of slabs. In areas on the CMB free of slabs, plume formation and eruption are expected to be frequent while the basal thermal boundary layer would be thin. However, in areas beneath slabs, the basal thermal boundary layer would be thicker and plume formation infrequent. Beneath slabs, a substantial amount of hot mantle can be trapped over long periods of time, leading to “mega-plume” formation. We predict that patches of low seismic velocity may be found beneath large-scale high seismic velocity structures at the core-mantle boundary. We find that the location, buoyancy, and geochemistry of mega-plumes will differ from those plumes forming at the edge of slabs. Various geophysical and geochemical implications of this finding are discussed.


Item Type:Article
Additional Information:Copyright 2002 by the American Geophysical Union. Received: 19 September 2001; Revised: 3 May 2002; Accepted: 16 July 2002; Published: 16 November 2002. We thank J. X. Mitrovica and T. Lay for their constructive reviews. Supported by NSF grants EAR-9814577 and EAR-0001966. This paper represents Contribution Number 8837 of the Division of Geological and Planetary Sciences, California Institute of Technology.
Group:Seismological Laboratory
Subject Keywords:subducted slabs; plumes; megaplumes; mantle convection; deep mantle; core-mantle boundary; 7207 Seismology: Core and mantle; 8121 Tectonophysics: Dynamics, convection currents and mantle plumes; 1213 Geodesy and Gravity: Earth's interior—dynamics (8115, 8120)
Record Number:CaltechAUTHORS:TANggg02
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:TANggg02
Alternative URL:http://dx.doi.org/10.1029/2001GC000238
Official Citation:Tan, E., M. Gurnis, and L. Han, Slabs in the lower mantle and their modulation of plume formation, Geochem. Geophys. Geosyst., 3(11), 1067, doi:10.1029/2001GC000238, 2002.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:1100
Collection:CaltechAUTHORS
Deposited By: Archive Administrator
Deposited On:19 Dec 2005
Last Modified:11 Jun 2015 12:58

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