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Numerical Modeling of Mantle Flow Beneath Madagascar to Constrain Upper Mantle Rheology Beneath Continental Regions

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posted on 2021-03-17, 10:41 authored by TA Rajaonarison, DS Stamps, S Fishwick, S Brune, A Glerum, J Hu
Over the past few decades, azimuthal seismic anisotropy measurements have been widely used proxy to study past and present-day deformation of the lithosphere and to characterize convection in the mantle. Beneath continental regions, distinguishing between shallow and deep sources of anisotropy remains difficult due to poor depth constraints of measurements and a lack of regional-scale geodynamic modeling. Here, we constrain the sources of seismic anisotropy beneath Madagascar where a complex pattern cannot be explained by a single process such as absolute plate motion, global mantle flow, or geology. We test the hypotheses that either Edge-Driven Convection (EDC) or mantle flow derived from mantle wind interactions with lithospheric topography is the dominant source of anisotropy beneath Madagascar. We, therefore, simulate two sets of mantle convection models using regional-scale 3-D computational modeling. We then calculate Lattice Preferred Orientation that develops along pathlines of the mantle flow models and use them to calculate synthetic splitting parameters. Comparison of predicted with observed seismic anisotropy shows a good fit in northern and southern Madagascar for the EDC model, but the mantle wind case only fits well in northern Madagascar. This result suggests the dominant control of the measured anisotropy may be from EDC, but the role of localized fossil anisotropy in narrow shear zones cannot be ruled out in southern Madagascar. Our results suggest that the asthenosphere beneath northern and southern Madagascar is dominated by dislocation creep. Dislocation creep rheology may be dominant in the upper asthenosphere beneath other regions of continental lithosphere.

Funding

National Science Foundation (NSF). Grant Number: EAR-1551864

History

Citation

Volume 125, Issue 2, February 2020, e2019JB018560

Author affiliation

School of Geography, Geology and the Environment

Version

  • VoR (Version of Record)

Published in

Journal of Geophysical Research. Solid Earth

Volume

125

Issue

2

Publisher

Wiley for American Geophysical Union (AGU)

issn

2169-9313

eissn

2169-9356

Acceptance date

2019-12-22

Copyright date

2020

Available date

2021-03-17

Language

English

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