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Regional Crustal Structure and Heat-Flow Prediction of the Mediterranean Using Gravity Inversion


The Mediterranean Sea consists of a complex mosaic of ocean basins of different age and origin. Predicting regional crustal structure and basement heat-flow, as input to petroleum-systems models, presents a significant exploration challenge in this area. We use gravity-anomaly inversion to determine Moho depth, crustal-basement thickness and continental lithosphere thinning-factor (1-1/β) across the Mediterranean. These results are in turn used to calculate top basement heat-flow history, including both transient and continental radiogenic-heat-productivity components. The methodology uses a 3-D spectral domain gravity inversion, incorporating corrections for lithosphere thermal gravity anomaly and magmatic addition from decompression melting. Lithosphere thinning-factor is used to determine the thickness of radiogenic continental crust and its heat-flow contribution, and also the transient heat-flow component for both oceanic and thinned rifted-continental-margin lithosphere. The radiogenic and transient heat-flow components, together with the background asthenosphere-derived heat-flow, are combined to predict heat-flow history from breakup to present-day. For each oceanic sub-basin of the Mediterranean we explore a range of rift and breakup ages to determine top basement heat-flow history and likely sensitivity to uncertainty within the models. Maps of crustal thickness and thinning factor show the present distribution of oceanic lithosphere and the location of the continent-ocean-boundary. Crustal cross-sections, with Moho depth determined from gravity inversion, show structure and magmatic type (magma poor, normal or magma rich) across the ocean-continent-transition and also the possible existence of hyper-extended continental crust. Digital grids of continental-lithosphere thinning and residual continental radiogenic-heat-productivity provide valuable input to petroleum-systems and basin-modelling studies. Delimiting the crustal type reduces some of the uncertainty associated with such work.