TECTONIC IMPLICATIONS OF LITHOSPHERIC STRUCTURE BENEATH SOUTHERN NEW ENGLAND RESOLVED BY MULTIPLE SEISMIC IMAGING TECHNIQUES

The eastern margin of North America was shaped by two supercontinent cycles, resulting in paleo-plate boundaries exposed at the surface. Accretion of Gondwanan-derived terranes and Mesozoic rifting also modified the lithosphere deep beneath the surface, as revealed by seismic discontinuities. To study these seismic discontinuities, we deployed a dense seismic array across the Appalachian orogen at the latitude of southern New England. Using data from the SEISConn array, the Ps receiver function imaging technique revealed a ~15 km offset in depth to Moho beneath the surface boundary between Laurentia and accreted terranes. Several other dipping discontinuities in the crust and mantle lithosphere, which may reflect paleo-subduction zones that facilitated terrane accretion, were also imaged. Discontinuities with complicated geometries may be better resolved using the scattered wavefield migration technique, which extends traditional 1-D receiver function analysis to 2-D model space. The large Moho depth offset is well resolved by both techniques and may reflect Ordovician subduction of Laurentia under a Gondwanan-derived terrane. Other discontinuities in the lithospheric mantle imaged by both techniques may constrain past subduction events and hotspot migration. Dipping discontinuities in the crust are too shallow to be accurately imaged with the wavefield migration technique, but their interpretation as crustal shear zones formed during terrane accretion can be further tested with the transverse component of receiver functions, which provides constraints on the anisotropic structure of these features. An accurate picture of the lithospheric structure reliably resolved using multiple seismic analysis techniques, combined with constraints from surface geologic mapping, can help constrain the tectonic history of southern New England including the complex nature of the Appalachian orogenic cycle, opening of the Atlantic, and post-tectonic modification of the lithosphere.