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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
Author(s) -
Geng Y.,
Powell C. A.,
Saxena A.
Publication year - 2020
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1029/2020jb020625
Subject(s) - geology , structural basin , lithosphere , mantle (geology) , seismology , basin and range province , basin and range topography , seismic tomography , geochemistry , geomorphology , tectonics
Three‐dimensional, high‐resolution crustal and upper mantle P and S wave velocity (Vp and Vs) models are presented for the central United States using body wave tomography. The study utilizes local and teleseismic data recorded by the Northern Embayment Lithospheric Experiment stations, the CERI New Madrid Seismic Network, the Earthscope Transportable Array, and the Ozark Illinois INdiana Kentucky Flexible Array. 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 magnitudes in the LVZ reach 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. The Illinois Basin velocity anomalies cannot be explained by elevated temperature alone and require compositional heterogeneity involving 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 a large igneous province, which convection models suggest is currently located below the central United States.