Rice University

Events at Rice

Thesis Defense

Graduate and Postdoctoral Studies
Earth Science

Speaker: Ara Alexanian
Masters Candidate

Late stages of breakup of the Galicia rifted margin

Friday, April 14, 2017
1:30 PM  to 4:30 PM

110  Dell Butcher Hall

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 over the years 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 This study presents previously unpublished pre-stack time migrated seismic data to the west of and integrated with a previously published swath line collected along the margin.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 new data are limited to 2D processing due to lack of geometric positioning control and are presented within a broader transect processed to pre-stack time migration. The presented swath line is also reprocessed to pre-stack depth migration in 3D. An interval velocity model was obtained by performing a migration velocity analysis of the sedimentary rocks in the upper portion of the seismic record. These migration velocities for the upper parts of the survey were combined with two separate, adjacent refraction velocity models for the deeper parts of the survey to process a final depth image of the data. This line shows the stratigraphy and rift related faulting of the Deep Galicia Margin. The combined seismic line shows what may be a boundary between exhumed mantle from the Galicia domain and true oceanic crust. Furthermore, some of the faulting and stratigraphy may be directly correlatable with similar features on the conjugate Newfoundland margin. The continental crust breaks up completely 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 R/V Marcus G. Langseth collected a 68km by 20km box of data from the Deep Galicia Margin that has been processed to pre-stack time migration. The interplay of fault structure with stratigraphy is interpreted in these data. There are 55 major Cretaceous aged faults in four fault 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 crustal fault blocks. Given the results, 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.

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