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Integrating Crustal Architecture and Syn-Rift Plate Kinematics

Abstract

The syn-rift phase of passive margin development has long been recognized as a critical time in the evolution of hydrocarbon systems. Lacustrine environments and restricted marine basins, which are prone to relative anoxia and thus organic matter preservation, often occur in rifted terraines, and in extreme cases of restriction, salt accumulations and evaporite seals may be deposited. The rifting process also establishes the distribution of extended continental crust and lithospheric mantle, as well as the presence of other potential exotic basement types including exhumed mantle, which have implications for heat flow and for sediment accommodation. While much work has been done to understand how continents break apart during the syn-rift phase, little has been done to establish a reliable and canonical means of extracting the syn-rift history on a margin by margin basis, within the framework of plate kinematics and deformable models. Most current efforts rely on the assumption that euler poles for oceanic spreading can be extrapolated back in time, into the syn-rift phase, and that extension ceases when a hypothetical uniform crustal thickness value has been achieved. This method, of course, requires an estimate of the modern day crustal architecture of the margin including: limit of oceanic crust (LOC), location and size of exotic crustal blocks, and the distribution of crustal thickness. Here we examine the uncertainties propagated into the syn-rift phase of plate kinematic models by uncertainties in crustal architecture. The examination is conducted by “retro-dicting” crustal thickness in the pre-rift Gulf of Mexico, using a series of popular plate kinematic models and crustal architecture solutions. We find a significant variance in the resulting estimates of syn-rift extension, and discuss methods to systematically identify and eliminate geologically-implausible solutions to both the crustal architecture and kinematic models. Specifically we show that statistical comparisons between reconstructed pre rift thickness, and crustal thickness behind the margin hingeline offers a less arbitrary means of establishing the syn-rift solution space, than attempting to achieve a singular uniform value for crustal thickness across the margin.