Lithospheric Evolution of the South‐Central United States Constrained by Joint Inversion of Receiver Functions and Surface Wave Dispersion.

In the present study, we use broadband seismic data recorded by 190 stations of the EarthScope program's Transportable Array to construct a 3‐D shear wave velocity model for the upper 180 km using a non‐linear Bayesian Monte‐Carlo joint inversion of receiver functions (RFs) and Rayleigh wave dispersion curves. Ambient noise and teleseismic data are used for obtaining Rayleigh wave phase velocity dispersion curves. A resonance removal filtering technique is applied to the RFs contaminated by reverberations from the thick sedimentary layers that cover most of the region. Our observations of the higher crustal shear velocities (∼3.40 km/s) beneath the Sabine Block (SB), along with the estimated relatively thicker crust (∼34.0 km) and lower crustal Vp/Vs estimates (∼1.80) in comparison with the rest of the Gulf Coastal Plain (GCP) (∼3.10 km/s for crustal shear velocities, ∼29.0 km for crustal thickness, and ∼1.90 for crustal Vp/Vs estimates), indicating that this crustal block has different crustal properties from the surrounding coastal plain regions. The southern Ouachita Mountains have a thin crust (∼30.0 km) and low mean crustal Vp/Vs value (∼1.73), suggesting that lower crustal delamination has occurred in this region. Low velocities in the upper mantle beneath most of the GCP are interpreted as a combined result of thin lithosphere, higher‐than‐normal temperatures, and possibly compositional variations. Plain Language Summary: The Gulf of Mexico Coastal Plain and its adjacent areas of the South‐Central United States contain some of the largest hydrocarbon reserves in the world. Thus an improved understanding about the formation mechanism and evolution of the region is important for both theoretical and practical reasons. In this study, we apply several computationally intensive techniques to image the upper 180 km of the Earth's interior beneath the South‐Central United States. Our results suggest that the crustal properties of the Sabine Block, located in the northern coast of the Gulf Coastal Plain (GCP), are different in comparison with the surrounding coastal plain regions. They are also consistent with the notion that the southern Ouachita Mountains have lost the lower part of its original crust into the deep mantle through a process called delamination. Low velocities are observed from approximately 30 to at least 180 km deep beneath most of the GCP, which are attributed to the thin lithosphere that allows the replacement of low‐velocity asthenospheric materials, higher‐than‐normal temperatures of the region, and probably also compositional changes beneath the GCP. Key Points: Results provide evidence that the Sabine Block has different crustal properties from the surrounding Gulf Coastal Plain (GCP)Lower crustal delamination beneath the southern Ouachita Mountains is suggested by a thin and felsic crustLow velocities in the upper mantle of the GCP are mainly caused by the thin lithosphere and high temperatures [ABSTRACT FROM AUTHOR]