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Joint local and teleseismic tomography in the central United States: exploring the mantle below the upper Mississippi Embayment and the Illinois Basin
  • Yu Geng,
  • Christine A. Powell,
  • Arushi Saxena
Yu Geng
University of Memphis

Corresponding Author:ygeng1@memphis.edu

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Christine A. Powell
University of Memphis
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Arushi Saxena
University of Memphis
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Abstract

Three-dimensional, high resolution crustal and upper mantle P- and S-wave velocity (Vp and Vs) models are presented for the central United States. The study utilizes local and teleseismic data recorded by the Northern Embayment Lithospheric Experiment stations, the New Madrid Seismic Network, the Earthscope Transportable Array, and the Ozark Illinois INdiana Kentucky Flexible Array. The Vp and Vs solutions are very similar and are well resolved in the depth range 40 to 400 km. Two anomalously slow regions are present below the Illinois Basin forming a northwest dipping low velocity zone (LVZ) extending from ~200 to 400 km. Maximum anomaly magnitude in the LVZ reaches about -4 % and -5% for Vp and Vs, respectively. The LVZ appears to connect to a well-documented LVZ located below the northern Mississippi Embayment. As is the case for the northern Mississippi Embayment, the Illinois Basin velocity anomalies cannot be explained by elevated temperature alone and require elevated orthopyroxene content in addition to an increase in iron and water content. The need for additional orthopyroxene suggests that the LVZ is being produced by metasomatism of mantle rocks by hydrous, silica-rich fluids ascending from a slab fragment trapped in or near the transition zone. This supports previous interpretations for the existence of the LVZ below the Embayment. We suggest that the LVZs below the Mississippi Embayment and the Illinois Basin are linked to the presence of the large igneous province Hess plateau currently located below the central United States by inverse convection models.
Oct 2020Published in Journal of Geophysical Research: Solid Earth volume 125 issue 10. 10.1029/2020JB020625