The Galicia margin offshore of Spain represents a magma poor end member of a rifted margin. The margin exhibits varied fault structures and complex seismic stratigraphy. The R/V Marcus G. Langseth acquired three dimensional seismic data in the Deep Galicia Margin in 2013.
These data are the main focus of this thesis and are used to describe the geology at this margin.

Seismic reflection and refraction data have been acquired along the Galicia margin to understand the process of rifting. This study presents previously unpublished pre-stack time migrated seismic data to the west of and integrated with a previously published swath line collected along the margin. The swath line is also reprocessed to pre-stack depth migration using an interval velocity model. Reflection tomography was performed to obtain a refined velocity model in the sedimentary units in the upper portion of the seismic record, which was combined with refraction velocity models for the deeper parts of the survey. The composite seismic line reveals structures that relate to the late stages of rifting at the Deep Galicia Margin, including what appears to be the boundary between exhumed mantle from the Galicia domain and oceanic crust, denoting the ocean-continent transition. Correlated structures and horizons between the conjugate Galicia and Newfoundland margins indicate a “breakup fault” responsible for the final detachment of the two continents. This mantle-penetrating fault likely continued to be active during the onset of oceanic spreading. Thus, a double asymmetry model predicts the formation of the Galicia and Newfoundland rifted margins.

The continental crust thins until breakup in the Deep Galicia Margin. Many previous rift models have been used to explain the sequence of faulting that accompanies the breakup of continental crust and exhumation of mantle there. The interplay of fault structure with stratigraphy is interpreted in the Galicia 3D data. There are 55 major Cretaceous aged faults interpreted in separate groups. Sediment basin formation may be related to the transitions between the fault groups. Four widespread horizons are seen in the volume, including two within fault blocks of continental crust. The final breakup of the continental crust may have been caused by a detachment fault that also truncates the S detachment fault. The later detachment fault is similar to faults seen in oceanic core complexes.