UNDERSTANDING THE LITHOSPHERIC SUTURE BETWEEN LAURENTIA AND GONDWANA: A PASSIVE SEISMIC EXPERIMENT IN THE SOUTHEASTERN U.S

The interpretation of an Alleghanian suture between Laurentian and Gondwanan crust in Georgia is supported by compelling geological and geophysical evidence. Beginning in Summer 2010, we will deploy an array of broadband seismic stations to constrain variations in properties of the crust and upper mantle across the Suwannee lithospheric suture and to probe the signatures of rifting and passive margin development in the crust and mantle beneath southern Georgia and Florida. The principal goal of these experiments is to constrain how accretion is accommodated in the mantle lithosphere. Specific questions to be addressed include the nature of the connection of the crustal suture to mantle structures, the dip of accretionary surfaces in the mantle (shallow or steep?), the existence of zones of strong anisotropy associated with concentrated zones of deformation, the polarity of subduction prior to continental collision, and evidence for delamination of the lithosphere. Broadband seismometers from the EarthScope Flexible Array will be deployed along two dense N-S lines that are centered over a prominent, crustal-wide zone of southward dipping reflections imaged in COCORP reflection profiles. The west and east lines will be 520 and 560 km long, respectively, and together will comprise 85 stations. Station spacing directly over the reflector zone will be 5 km; spacing will increase to 10 km, 20 km, and ultimately to 35 km towards the ends of the lines. Work along the western line will begin in Summer 2010 with the deployment of 7 test stations; the remaining stations along the western line will be deployed in Summer 2011, followed by deployment of stations along the eastern line in Summer 2012 to coincide with the arrival of EarthScope Transportable Array stations in the region. Stations will remain in place until Summer 2014. The experiment is designed to constrain variations in crust and upper mantle properties across the Suwannee suture. Recordings of teleseisms will be used to map variations in Vs in the shallow crust and variations in crustal thickness and Vp/Vs, image a possible mantle continuation of the crustal suture observed in the COCORP data, and map lateral variations in thickness, velocity, shear-wave attenuation, and anisotropy within the mantle lithosphere.