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Integrated Quantitative Analysis of Deep Reflection Seismic and Gravity Anomaly Data: Application to Eastern Gulf of Mexico OCT Structure and Location

Abstract

Knowledge of the structure of the ocean-continent transition (OCT) and the location of the continent-ocean boundary (COB) are of critical importance for predicting heat-flow history and evaluating petroleum systems in deep-water frontier exploration. Integrated quantitative analysis of deep seismic reflection and gravity anomaly data has been applied to the Florida margin of the Gulf of Mexico in order to determine OCT structure, COB location and magmatic type using SuperCache deep long-offset seismic reflection data. Gravity anomaly inversion, incorporating a lithosphere thermal gravity anomaly correction, has been used to determine Moho depth, crustal basement thickness and continental lithosphere thinning. Residual depth anomaly (RDA) analysis has been used to investigate OCT bathymetric anomalies with respect to expected oceanic values, and subsidence analysis has been used to determine the distribution of continental lithosphere thinning. The combined interpretation of these independent quantitative measurements is used to determine OCT structure, COB location and margin magmatic type. This integrated approach has been validated on the Iberian margin where ODP drilling provides ground-truth. In addition a joint inversion technique using deep seismic reflection and gravity anomaly data has been applied to the SuperCache 3200-3201 profile across the Florida margin in the eastern Gulf of Mexico. The joint inversion method solves for coincident seismic and gravity Moho and calculates the lateral variations in crustal basement densities and velocities. This joint inversion of deep seismic reflection and gravity data shows that there are two distinct types of oceanic crust; the thickness of proximal oceanic crust adjacent to the COB is between 7.5km and 8km while more out-board westerly oceanic crust is between 6.5km and 7km. Sensitivities to magmatic addition have been considered; a slightly magma rich solution is preferred for the proximal oceanic crust. The joint inversion also predicts that the western (more distal) oceanic crust has a lower crustal basement density and seismic velocity than more proximal oceanic crust. Application of joint inversion of reflection and gravity data to the Florida platform suggests a substantial thickness of sediments beneath the mid Jurassic unconformity. The sediment and crustal thickness corrected RDA is near zero implying little mantle dynamic topography affecting the Florida margin of the eastern Gulf of Mexico.