Crustal and uppermost mantle structure of the Porcupine Basin west of Ireland from seismic and gravity methods

Abstract : The Porcupine basin is a failed rift that formed during the opening of the North Atlantic Ocean. Here, we provide additional insights into the crustal structure of the northern Porcupine Basin and assess the degree of crustal extension from long streamer seismic data and free-air gravity modelling. Recent re-processing of the 2013/2014 streamer data involved de-multiple and de-noise processing with pre-stack-depth migration using velocity models derived from reflection travel time tomography and full waveform inversion. Forward modelling of satellite gravity data was used to constrain the velocity and mass density of the basement and lower crust, where the seismic constraints are limited. Prior knowledge, from previous geophysical and geological studies, was included to guide the modelling and reconcile the gravity data with the seismic sections. It also served to minimize the non-uniqueness inherent in the forward problem. Crustal thinning occurs across the basin axis and increases southwards. We infer maximum stretching factor (β) at the basin axis, increasing from ∼4 to 6 in the North Porcupine at 52.5°N to >10 at ∼51°N in the Central Porcupine. The gravity modelling supports the presence of mantle serpentinisation, and the high β implies that crustal break up and mantle exhumation may have locally occurred in the Central Porcupine Basin, in agreement with previous seismic tomographic studies. Basaltic melt generation in the centre of the basin where the maximum bulk stretching factor exceeds10 in the hyper-extended crust may have led to localized sea-floor-spreading.