Investigating Lithospheric Evolution Beneath the Southern and Northeastern United States

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Throughout Earth?s history, the tectonic plates that make up the lithosphere have converged to form super-continents and then pulled apart over time-scales of hundreds of millions of years. The southern U.S. near the Gulf Coast and the eastern U.S. bordering the Atlantic experienced two cycles of super-continent formation and break-up. These episodes of collision and rifting altered the crust and mantle lithosphere of the North American plate, thickening these layers in some regions, thinning them in others, and producing distinctive structures by aligning mineral grains and melting small amounts of rock. In this project we will use earthquake waves to construct three-dimensional models of the crust and mantle lithosphere, and we will interpret these models to better understand how continental collision and rifting affect continental lithosphere.The goal of this work is to improve resolution of crust and mantle structure in the southern and eastern U.S. in order to better understand lithospheric evolution and modification through the last Wilson cycle. The southern and eastern margins of the North America continent experienced two complete Wilson cycles of orogeny and rifting, leaving varied signatures of deformation and magmatism in the crust and mantle lithosphere of these regions. However, many aspects of crust and mantle structure remain poorly known at the scales relevant to distinguishing the effects of orogeny, rifting, and other processes such as hotspot interaction. Using data from the NSF EarthScope USArray/Transportable Array (TA), now completed in the contiguous U.S., we propose to image crust and mantle seismic structure in new detail. We will focus on two regions: one spanning the southern craton edge, the entire Ouachita orogeny and the Gulf of Mexico coastal plain, and the other containing the eastern craton edge, the central and northern Appalachians, and the Atlantic coast. We will use seismic data from TA stations, supplemented by other temporary and permanent broadband stations, to image crustal and mantle discontinuities using Sp and Ps receiver functions, construct 3-D anisotropic models based on Rayleigh wave, Love wave and shear-wave-splitting analyses, and we will integrate these data and methods through joint analyses and inversions. The seismic models will be used constrain the style and geometry of deformation in the crust and mantle lithosphere due to the last episodes of orogeny and rifting. This interpretation will be guided by geological and active source indicators of deformation in the shallow crust and by the type and age of magmatism across the region, bearing in mind that some facets of crust and mantle structure may reflect events that predated or followed the last cycle of orogeny and continental rifting. Variations in the impact of orogeny and rifting on the lithosphere will be compared between and within the study regions. The proposed project will support the education and career development of graduate students at the University of Houston and at Brown. It will also contribute to undergraduate senior theses, lab exercises and group research projects in undergraduate and graduate courses, and to science outreach activities with local public schools. Students from diverse backgrounds will be recruited to participate in this research.