Modification of lithospheric structure via subduction, terrane accretion, and rifting: A case study beneath Connecticut

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The bedrock geology of the eastern United States is extraordinary in its complexity. This complexity reflects a range of plate tectonic processes that have affected eastern North America over geologic time. These processes include the formation and breakup of supercontinents, the accretion of new landmasses onto the continental edge, and widespread volcanic activity due to subduction and continental rifting. The state of Connecticut, though relatively compact in area, represents a prime opportunity to study this range of fundamental Earth processes. This is because Connecticut's geology reflects several phases of mountain building and terrane accretion during the formation of the Appalachian Mountains and the Pangea supercontinent, as well as the later breakup of Pangea and the formation of the Atlantic Ocean basin. This project will use data from an array of 15 seismic stations deployed across northern Connecticut to study the deep structure of the crust and mantle beneath the state, using recordings of seismic waves from distant earthquakes. The team will use images of this deep structure to answer fundamental questions about how supercontinents are formed and break up, as well as how plate tectonic processes such as subduction, rifting, and terrane accretion affect the evolution of the crust and upper mantle. The project includes a component of outreach to high school science teachers, enabling teachers to spend one week in the field collecting data and learning about Connecticut geology, as well as developing a classroom exercise that uses seismic data from the project.The investigators will analyze data from the Seismic Experiment for Imaging Structure beneath Connecticut (SEISConn), a deployment of 15 broadband seismometers in a dense linear array across northern Connecticut. The array occupies a region of the Appalachian Orogen that encompasses a striking variety of accreted terrane structures, as well as the Hartford Basin, a Mesozoic rift structure resulting from the breakup of Pangea. They will apply a suite of imaging techniques to SEISConn data, focusing on the imaging of discontinuity structure, seismic velocity structure, and seismic anisotropy within the crust and lithospheric mantle. The project is motivated by three major science questions: 1) How did episodes of subduction and terrane accretion during Appalachian oogenesis affect crustal and mantle lithospheric structure, and how does present-day deep structure correspond to surface geology? 2) How was the structure of the crust and mantle lithosphere affected by (failed) rifting during the Mesozoic, and how does the structure beneath the Hartford Rift Basin compare to structure across the (ultimately successful) rifted margin of eastern North America? 3) How was the crust and mantle deformed during subduction, terrane accretion, and rifting? This project will apply a range of analysis techniques to SEISConn data, including P-to-S and S-to-P receiver function analysis, ambient noise tomography, wavefield migration imaging, and shear wave splitting. The final phase of the project will involve the testing of specific hypotheses about past tectonic processes that were formulated based on geologic observations. This project will support the continuation of the successful Field Experiences for Science Teachers (FEST) program at Yale, which provides one week of field seismology experience to Connecticut-based high school science teachers.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.