[First Hit]

AAPG Annual Convention and Exhibition

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Equatorial Atlantic Deep-Water OCT Previous HitStructureNext Hit and Previous HitCrustalNext Hit Type From Satellite Gravity Inversion

Abstract

Determining the Previous HitstructureNext Hit of the ocean-continent-transition (OCT), the location of the continent-ocean-boundary (COB) and the composition of Previous HitcrustalNext Hit basement are substantial challenges during deep-water exploration. Inversion of satellite-derived free-air gravity-anomaly data, using a technique which allows for (i) the thermal state of the lithosphere following rifting and breakup and (ii) magmatic addition to the crust during rifting and breakup, provides a useful method for mapping Previous HitcrustalNext Hit Previous HitstructureNext Hit and Previous HitcrustalNext Hit type across global rifted margins. Maps of Previous HitcrustalNext Hit thickness and continental-lithosphere thinning-factor may be used to determine COB location and the distribution of oceanic lithosphere. Previous HitCrustalNext Hit cross-sections using Moho depth from gravity inversion allow OCT Previous HitstructureNext Hit and basement composition to be constrained. We have used this gravity inversion technique to investigate the Previous HitcrustalNext Hit Previous HitstructureNext Hit of the Equatorial Atlantic conjugate margins. Using maps of Previous HitcrustalNext Hit thickness and continental-lithosphere thinning-factor, with the shaded-relief free-air gravity anomaly superimposed, we can improve the determination of pre-breakup rifted-margin conjugacy and the trajectory of sea-floor spreading during ocean basin formation. These maps illustrate how the Equatorial Atlantic opened as a set of oblique rift-transform segments. A set of cross-sections has been extracted from the results of the gravity inversion along both equatorial margins. These illustrate the Previous HitcrustalNext Hit Previous HitstructureNext Hit of both rifted-margin segments and transform-margin segments. The maps and cross-sections are used to delineate OCT Previous HitstructureNext Hit, Previous HitcrustalNext Hit type and their lateral variation. On both margins anomalously thick crust is resolved along a number of oceanic fracture zones. Three possible origins for this are discussed, (i) continental crust attenuated along the fracture zones, (ii) oceanic crust magmatically thickened at the fracture zones, (iii) oceanic crust thickened by transpression along the fracture zones. Gravity inversion alone cannot discriminate between these possibilities. Maps and cross-sections show the existence of both magma-poor and magma-rich margin segments, in addition to large areas of “normal” magmatic addition. Using maps of Previous HitcrustalTop-thickness and thinning-factor as input to plate reconstructions, the regional palaeogeography of the Equatorial Atlantic at breakup and the subsequent development of deep-ocean connectivity have been examined.