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Deep structure of the Porcupine Basin using seismic refraction

Author(s): Louise Watremez University of Southampton, Southampton, UK, UK
Manel Prada Geophysics Section, Dublin Institute for Advanced Studies, Dublin, Ireland
Chen Chen University of Southampton, Southampton, UK/National Oceanography Centre, Southampton, UK
Tim Minshull University of Southampton, Southampton, UK
Brian O’Reilly Geophysics Section, Dublin Institute for Advanced Studies, Dublin, Ireland
Tim Reston School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, UK
Gerlind Wagner Geomar Helmholtz Centre for Ocean Research, Kiel, Germany
Gerlind Wagner Geomar Helmholtz Centre for Ocean Research, Kiel, Germany
Viola Gaw Geomar Helmholtz Centre for Ocean Research, Kiel, Germany

Dirk Kläschen (5), Patrick Shannon (6)

(5) Geomar Helmholtz Centre for Ocean Research, Kiel, Germany (6) School of Earth Sciences, University College Dublin, Dublin, Ireland

The Porcupine Basin is a narrow V-shaped failed rift basin of Permo-Triassic to Cenozoic age, with the main rifting phase in the Late Jurassic to Early Cretaceous. It is located offshore SW Ireland. A previous study shows increasing stretching factors from less than 1.5 to the north to more than 6 to the south using basin subsidence analysis. A ridge feature, the Porcupine Median Ridge (PMR), has been identified in the middle of the southernmost part of the basin. During the last three decades, this ridge has been successively interpreted as a volcanic structure, a diapir of partially serpentinised mantle, or a block of continental crust. Its nature still remains debated today. In this study we use a seismic refraction profiles acquired across the northern and southern Porcupine Basin to derive P-wave velocity models using tomography modelling, following a layer-stripping strategy. We use the data from two 300 km long shot lines recorded by 25 and 30 seismic receivers, for the northern and southern lines, respectively. The profiles are approximately 90 km apart, oriented west-east and cross the entire basin from the Porcupine Bank to the Irish Continental Shelf. This two seismic refraction lines are coincident with seismic reflection profiles, which are used to help seismic velocities interpretation. Thus, we image the deep structure of the basin, the geometry of the continental thinning from margin to margin, and the PMR. Our main results are (1) an asymmetric crustal thinning, especially along the southernmost profile, implying some simple shear during the extension, (2) a wider zone of ultra-thinned crust along the southern profile (~ 90 km) than the northern one (~ 30 km), with thinning factors up to 6 along the northern profile and up to 10 along the southern profile, (3) a low velocity mantle, with velocities < 7.5 km/s, together with ultra-thinned crust, implying up to 20% upper-mantle serpentinisation, and (4) velocities of 5-5.7 km/s in the PMR, associated with a high velocity zone in the sedimentary sequence. This observation argues in favour of an igneous nature of this ridge and associated features. The project is funded by Petroleum Infrastructure Programme (PIP).


Title:
Deep structure of the Porcupine Basin using seismic refraction
Type:
Oral
Origin:
Academia
Day:
2
Session:
2
Daily sequence no.:
17
Lead author last name:
Watremez
Lead author first name:
Louise
Affiliation(s):
University of Southampton, Southampton, UK
Country:
UK
Abstract status:
ok
UID:
62