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Compressible thermochemical convection and application to lower mantle structures

Tan, Eh and Gurnis, Michael (2007) Compressible thermochemical convection and application to lower mantle structures. Journal of Geophysical Research B, 112 (B6). Art. No. B06304. ISSN 0148-0227. http://resolver.caltech.edu/CaltechAUTHORS:20121119-134909606

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Abstract

A new finite element code for compressible thermochemical convection is developed to study the stability of a chemical layer at the base of the mantle. Using composition-dependent compressibility and a density difference between compositions at a reference pressure, a composition-dependent density profile is derived. Together with depth-dependent thermal expansion, this combination of parameters yields a wide range of dynamic evolutions for the chemical layer. The chemical structures are classified into five major categories (classical plumes, mushroom-shaped plume, domes, ridges, and continuous layers) and a few abnormal cases, such as hourglass-shaped plumes and columnar plumes. Several models have a chemical structure morphologically similar to the African low V_S structure in the lower mantle, at least at a single time. Guided by our models, several dynamic scenarios are proposed for the dynamic nature of the lower mantle low-velocity structures (a.k.a. superplumes), including plumes at an early stage, plume clusters, ridges, passive piles, sluggish domes, and high-bulk-modulus domes. We predict seismic velocity anomalies from these dynamic models. The thermoelastic parameters used in the conversion are additional constraints. We compare the density structure with normal mode inversion, the predicted seismic signature observations, and the required thermoelastic parameters with mineral physics data. Among the proposed scenarios, only the scenario of high-bulk-modulus domes satisfies all constraints simultaneously. The implication on the geochemistry and mineralogy of lower mantle chemical structures is discussed.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1029/2006JB004505DOIUNSPECIFIED
http://www.agu.org/pubs/crossref/2007/2006JB004505.shtmlPublisherUNSPECIFIED
Additional Information:© 2007 American Geophysical Union. Received 13 May 2006; accepted 14 February 2007; published 13 June 2007. This research has been supported by NSF grants EAR-0205653 and EAR-0215644. We thank Don Helmberger for continuous discussion during the course of this work. This work represents contribution 9165 of the Division of Geological and Planetary Sciences, California Institute of Technology.
Group:Seismological Laboratory
Funders:
Funding AgencyGrant Number
NSFEAR-0205653
NSFEAR-0215644
Subject Keywords:Compressible convection; thermochemical convection; superplumes; Geodesy and Gravity: Earth's interior: dynamics (1507, 7207, 7208, 8115, 8120); Seismology: Mantle (1212, 1213, 8124); Tectonophysics: Earth's interior: composition and state (1212, 7207, 7208, 8105); Geochemistry: Composition of the moon; Mineral Physics: Equations of state
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Caltech Division of Geological and Planetary Sciences9165
Record Number:CaltechAUTHORS:20121119-134909606
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20121119-134909606
Official Citation:Tan, E. and M. Gurnis (2007), Compressible thermochemical convection and application to lower mantle structures, J. Geophys. Res., 112, B06304, doi:10.1029/2006JB004505.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:35547
Collection:CaltechAUTHORS
Deposited By: Jason Perez
Deposited On:20 Nov 2012 00:04
Last Modified:11 Jun 2015 12:59

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