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Abstract:
In this investigation we model solid Earth deformation as constrained by vertical displacement of the Lower Mississippi River long profile over the past ~80 kyr. These observations are compared to output from a model that simulates glacial isostatic adjustment and sedimentary isostatic adjustment using a spherically-symmetric, viscoelastic Earth model. Observations of long-profile displacement based on optically-dated sediment cores, were revised to account for the effect of fault displacement in the southern end of the long profile inferred in some recent studies. Due to the relatively localized sediment loading associated with the Mississippi Delta System, the vertical displacement of the long profile over the past ~80 kyr is highly sensitive to lithospheric structure. For this reason, these observations offer a valuable opportunity to constrain mechanical properties of the lithosphere beneath the south-central United States. To pursue this opportunity, we consider multiple model scenarios in which the lithosphere is either entirely elastic (a common assumption in surface loading studies) or has internal viscosity structure. In the latter case, viscosity structures are determined using a range of plausible geothermal gradients and seismic constraints on Moho depth. In the elastic case, model lithosphere thicknesses are fixed at 46 km, 71 km, 96 km, or 120 km. For each modelling scenario (elastic vs viscous), constraints on lithosphere thickness and structure, and the ability of the model to match the observations will be presented.
