AAPG Europe Regional Conference, Global Analogues of the Atlantic Margin

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Reassessment of the structure of the Galicia Interior Basin from new seismic images: Implications for the West Iberia Margin formation

Abstract

The West Iberia continental margin is one of the best studied non-volcanic margins of the world, representing a classical end-member model. Nevertheless, to date most of the works have focused on the tectonic structure of the Deep Galicia Margin and Iberian Abyssal Plain segments, where final breakup occurred. However, complete knowledge involves the integration of all structural elements in the regional geodynamic context. In this sense, the Galicia Interior Basin (GIB) represents the necessary link to understand the mechanisms of extension from the little extended shelf to the areas where continental breakup finally occurs. The GIB is a ~3 km deep bathymetric trough located immediately west of the West Iberia continental platform containing up to 8 km of sediment and the basement locally thinned to fewer than 8 km. It extends in a N-S trend along more than 100 km between the NW Iberian continental shelf and the Galicia Bank. The GIB is considered as an aborted rift in the context of the opening of the North Atlantic rift system, but its role during rifting is not well understood. We presented a set of reprocessed multichannel seismic transects acquired across the GIB. By applying modern processing techniques on different vintage seismic profiles, we have been able to obtain high-quality images displaying the entire crustal structure. We used Tau-P and Wiener predictive deconvolution modules, and multiple attenuation by both radon filtering and wave-equation-based surface-related multiple elimination (SRME) to significantly increase the signal to noise ratio. The processing improved the image of the complex basement structure and deep sedimentary units, which was unclear in previous publications. We processed these lines up to post-stack time migration to integrate them with existing data sets. The reprocessed seismic lines run perpendicular to the margin’s trend from the continental shelf across the GIB to the Galicia Bank, providing the opportunity to study the 3D tectonic structure of the GIB. The new high-quality images show syn - and post -rift sediment, tilted fault blocks, well-defined top-of-the-basement reflections, and also intra-basement and Moho reflections that offer new information about the tectonic structural style during rifting. The data display variation in the amount and distribution of crustal extension across the basin, which allows new speculations on the reasons for the rift failure at the GIB in the context of the opening of the West Iberia margin.