SCIENTIFIC PROBLEMS AND LITHOSPHERIC TARGETS: THE NORTHERN EMBAYMENT LITHOSPHERE EXPERIMENT

Passage of the EarthScope TA stations across the Mississippi Embayment (ME) provides an opportunity to investigate lithospheric structure associated with active deformation and an ancient, major, intracratonic rift. The ME is a first-order geological structure of the North American continent but the reason for basin subsidence is enigmatic; subsidence began in Late Cretaceous and is not linked to a major tectonic episode. The lithosphere below the ME has a long and complex geological history of rifting, uplift, and subsidence over at least two Wilson cycles. In addition, the active New Madrid seismic zone (NMSZ) is located in the upper crust below the northern ME. We suggest that lithospheric heterogeneity ultimately controls the dynamic processes associated with ME subsidence and the NMSZ. We suggest further that the mantle lithosphere will show anomalous heterogeneity related to surface features and buried Phanerozoic rift geology. Investigating ancient failed rift lithospheric structure helps constrain the mantle dynamics associated with the rifting process. Major issues we wish to address are 1) the primary differences in lithospheric structure between the ME and the surrounding region, 2) the nature of early Cambrian rifting and relationship to pre-existing structure, 3) the dynamic processes responsible for ME subsidence, and 4) the relationship of the NMSZ to lithospheric structure. Joint interpretation of compressional and shear velocity tomography, potential fields, transfer/receiver functions, and depth-dependant anisotropy images generated using traditional and new techniques, should help unlock the enigma of the NMSZ and reveal how ancient tectonic events continue to influence the present via inherited lithospheric structure.