Gulf of Mexico crustal structure and plate kinematics from gravity inversion

An understanding of crustal thickness, ocean-continent-transition structure, the distribution of oceanic lithosphere and kinematic evolution is a critical component of petroleum systems evaluation in the Gulf of Mexico (GoM) and elsewhere. Using public-domain data and OCTek 3D gravity inversion, we have produced regional grids and maps of Moho depth, crustal-basement thickness, continental-lithosphere thinning-factor and residual continental-crustal-thickness for the GoM. Crustal-basement thickness and lithosphere thinning from the 3D gravity inversion show the distribution of oceanic crust within the GoM and constrain continent-ocean-boundary location.

Superposition of shaded-relief satellite free-air gravity anomaly onto maps of crustal-basement thickness and lithosphere thinning from gravity inversion show clearly the pattern and location of the extinct ocean-ridge and transform segments within the western and central GoM. These in turn reveal sea-floor spreading trajectory and provide important indications of pre-breakup rifted-margin conjugacy. By aligning small-circles with the transform faults visible in the free-air gravity data, the poles of rotation for the opening of the GoM can be refined. As a result of doing this we find that the opening of the GoM occurred in two stages. Initial rifting and breakup occurred along a N-S trajectory with the Yucatan block still linked to South America and to which the West Florida margin acted as a transform boundary. In the second stage, subsequent propagation of sea-floor-spreading between Yucatan and South America caused the Yucatan block to rotate anti-clockwise, resulting in sea-floor spreading within the GoM occurring about a pole locally-situated off the SW coast of Florida. In this second stage of GoM formation, the West Florida margin becomes an extensional feature. By refining the plate-reconstruction models in this way, we also gain a better insight into the linked development of the GoM in the context of the formation of the early Central Atlantic.

Crustal cross-sections using Moho depths from the 3D gravity inversion show the form of the ocean-continent transition, the distribution of crustal type (continental crust, oceanic crust, exhumed mantle) and help constrain models for petroleum-system development in the overlying stratigraphy. Building on this new understanding of kinematics in the GoM, flexural-backstripping and subsidence modelling, driven by lithosphere thinning/beta-factors from gravity inversion, have been used to predict the evolution of palaeobathymetry through the post-breakup history of the eastern GoM.