Seimic Structure of the Crust and Upper Mantle of Porcupine Basin from Wide-Angle Data

The evolution of continental rifted margins plays an important role in understanding the geological process of continental extension. As a key rifted basin located to the southwest of Ireland, the Porcupine Basin is a large V-shaped sedimentary basin of Late Palaeozoic to Cenozoic age. It formed during the opening of Atlantic Ocean, around Mid-Late Jurassic time. A geological feature named Porcupine Median Ridge (PMR) is identified at the southernmost part of the basin. However, the origin of PMR has remained debated, with serpentinization, volcanic activity and crustal faulting being suggested. Previous studies, mainly using seismic reflection and gravity data, show an increasing stretching factor from north to the south (from less than 1.5 to greater than 6). Wide-angle seismic data acquired along a ca. 100 km long profile across the basin axis yield new insights into the crustal and upper mantle structure. During this study, both refractions and reflections recorded by the OBS are used to perform a joint travel-time inversion, and a 2D P-wave velocity model has been obtained which contains information about the sedimentary, crustal and upper mantle structure. Multi-channel seismic data have been used to constrain the accuracy of all the seismic phases. The tomographic model is consistent with the forward modelling result. Analysis of the velocity features from both models reveals the crustal thickness at the south Porcupine Basin is up to 12 km in the middle of the basin, and then gradually decreases to 10 km under the PMR. Thus, the stretching factor is significantly lower than that inferred from former studies. Based on the results, we discuss the rifting process and the geological nature of the PMR. This project is part-funded by the Irish Shelf Petroleum Studies Group (ISPSG} of the Irish Petroleum Infrastructure Programme Group 4.