New evidence for the origin of the Porcupine Median Volcanic Ridge: Early Cretaceous volcanism in the Porcupine Basin, Atlantic margin of Ireland

Abstract

Two‐dimensional pre‐stack depth migrated seismic reflection data, gravity and velocity models are used to assess the nature and origin of a prominent, buried ridge, the Porcupine Median Volcanic Ridge (PMVR) within the Porcupine Basin, offshore Ireland. The debate on the origin of the PMVR during the past 30 years has followed the evolution of the concept of continental margin genesis. In this paper, the origin of the ridge is evaluated on the basis of the internal geometry and velocity structure, revealed by the seismic data. Implication of the presence of these type of ridges in hyper‐extensional rifted margins is discussed and compared with other margins. The analysis indicates that the ridge is an extrusive volcanic ridge, probably tholeiitic in composition, constructed by stacked hyaloclastite deltas and topped by carbonate platforms. The results invalidate previously proposed models involving highly rotated fault blocks and the serpentinite mud volcanism. The extension magnitude analysis suggests a highly stretched setting where limited mantle serpentinization may have occurred, but the architecture and velocity of the PMVR demonstrates that it is made of lower velocity materials than serpentinite. During the opening of the North Atlantic, the PMVR represents the northern time‐equivalent magmatic event expressed along the Newfoundland‐Iberia‐Galicia, recorded by the J anomaly that originate from Cretaceous volcanic deposits.