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Lower mantle structure from paleogeographically constrained dynamic Earth models

Bower, Dan J. and Gurnis, Michael and Seton, Maria (2013) Lower mantle structure from paleogeographically constrained dynamic Earth models. Geochemistry Geophysics Geosystems, 14 (1). pp. 44-63. ISSN 1525‐2027. http://resolver.caltech.edu/CaltechAUTHORS:20130523-075034112

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Abstract

Seismic tomography reveals two large, low-shear velocity provinces (LLSVPs) beneath Africa and the Pacific Ocean. These structures may have existed for several 100 Myr and are likely compositionally distinct based on observed seismic characteristics interpreted in light of geodynamic models and mineral physics constraints. We investigate the dynamics of the LLSVPs through the use of evolutionary models of thermochemical convection from 250 Ma to present day. We use a spherical convection model in which the anomalous structures have a high bulk modulus, consistent with seismic interpretation. A new progressive assimilation method incorporates constraints from paleogeography using a refined plate history model (with 1 Myr time spacing) to guide the thermal structure of the lithosphere and steer the thermal evolution of slabs in the uppermost mantle. The thermochemical structures deform and migrate along the core-mantle boundary (CMB) through coupling to plate motions and in response to slab stresses. The models produce a ridge-like anomaly beneath Africa and a rounded pile beneath the Pacific Ocean, which at present day agrees with tomography, waveform modeling, and other geodynamic studies. Plumes emanate from the margins of the domes and ridges of thickened boundary layer between the domes. Dense and viscous slabs can undermine the stability of high bulk modulus structures at the CMB. High bulk modulus structures are not necessarily required to satisfy dynamic constraints on the LLSVPs.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/ 10.1029/2012GC004267 DOIUNSPECIFIED
http://onlinelibrary.wiley.com/doi/10.1029/2012GC004267/abstractPublisherUNSPECIFIED
Additional Information:© 2013 American Geophysical Union. Received 5 June 2012; Revised 9 November 2013; Accepted 13 November 2012; Published 30 January 2013. We obtained CitcomS version 3.0 from the Computational Infrastructure for Geodynamics (CIG). GPlates is developed at the University of Sydney, the California Institute of Technology, and the Geological Survey of Norway (available from http:// www.gplates.org). We thank Eh Tan for providing guidance on code modification and useful discussions. Comprehensive and thoughtful reviews from Paul Tackley, Allen McNamara, and Associate Editor Bernhard Steinberger enhanced the manuscript. Most figures in this paper were produced using GMT. D.J.B. and M.G. acknowledge NSF grants EAR-0855815 and EAR- 0810303. M.S. acknowledges Australian Research Council grant DP0987713.
Group:Seismological Laboratory
Funders:
Funding AgencyGrant Number
NSFEAR-0855815
NSFEAR-0810303
Australian Research Council (ARC) DP0987713
Subject Keywords:LLSVP; core-mantle boundary; thermochemical convection; mantle structure
Record Number:CaltechAUTHORS:20130523-075034112
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20130523-075034112
Official Citation:Bower, D. J., M. Gurnis, and M. Seton (2012), Lower mantle structure from paleogeographically constrained dynamic Earth models, Geochem. Geophys. Geosyst., 14, 44–63, doi:10.1029/2012GC004267
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:38645
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:23 May 2013 15:31
Last Modified:11 Jun 2015 12:44

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