Evidence for pre-Cretaceous rifting in the Rockall Trough: an analysis using quantitative plate tectonic modelling

Abstract

Plate tectonic reconstructions of the North Atlantic Margin, west of Britain and Ireland have been generated using computer modelling software. A particular emphasis has been placed on the timing of rift phases within the Rockall Trough as this has significant implications for the distribution of Mesozoic hydrocarbon source rocks. A variety of geophysical and bathymetric data have been integrated to update existing plate boundary definitions, which has improved the resolution of the modelling. Forward and reverse modelling studies were then employed to quantify the amount of rifting in the Rockall Trough. Present-day plate outlines were contracted to discover the amount of intra-plate deformation required for a geometric fit. These results were then compared with the effects of contracting plate outlines by specified amounts using β factors from independent datasets from the Rockall Trough and adjacent areas. The reconstructions suggest that the majority of rifting occurred in the mid to Late Cretaceous and continued into the Eocene. They also indicate the occurrence of at least one episode of pre-Cretaceous rifting corresponding to a β factor of 1.6. The results of this study are corroborated by an independent structural and stratigraphic basin modelling project that examined the crustal evolution of the Rockall Trough. This produced a range of model solutions which, when constrained by data from this study and elsewhere, suggests a best-fit solution which requires a substantially thinned pre-rift crust, best explained by a pre-Cretaceous basin. The implications of the presence of an older rift system are favourable for hydrocarbon exploration in the area. Regionally there are important petroliferous Triassic to Jurassic rift systems and it is likely that an older rift system in the Rockall Trough would be of a similar age with significant potential to be hydrocarbon bearing.