8 July, 2009 (16:00 GMT), 5 Merrion Square, Dublin 2.

Speaker: Kim Welford (Memorial University of Newfoundland in St. John’s, Canada).
Title: Lithospheric density variations and Moho structure of the Irish rifted continental margin from constrained 3 D gravity inversion.

Abstract:

The structurally complex Irish margin was separated from its conjugate pair, the northern Flemish Cap/Orphan Basin region, during Late Cretaceous rifting of the North Atlantic. While crustal-scale 2-D seismic surveys have been collected across many parts of the margin, the results generated from these surveys cannot easily be interpreted in a regional sense due to their sparse sampling. We have undertaken a 3-D gravity inversion of the free air data over the Irish margin in order to generate a 3-D density anomaly model that can be compared with the seismic results and used to gain insight into regions lacking seismic coverage. We use the GRAV3D inversion algorithm and constrain our inverted model with bathymetric and sediment thickness information. We are able to closely reproduce the observed gravity anomalies over the margin and use the resultant density anomaly model to interpret the regional Moho structure by identifying a density isosurface appropriate for the crust-mantle
transition. Our interpreted Moho shows good correspondence with Moho depths from seismic results while providing a more detailed Moho depth map over the region. This map allows the lateral extent of crustal thinning beneath the Rockall Trough, the Porcupine Seabight Basin and south of Goban Spur to be investigated. We present regional cross-sections through the 3-D model to highlight lateral variations in Moho structure and lithospheric densities. We also map thickness variations in upper, middle and lower crustal densities across the margin. These maps may be revealing zones of exhumed serpentinized mantle in the Porcupine Basin, the Rockall Basin and outboard of Goban Spur and the Porcupine High. Anomalous zones of high density in the lower crust off the southern margin the Celtic Platform into the Biscay Abyssal Plain may provide evidence for underplating. Ultimately, the insights provided by our results must act as constraints for future paleoreconstructions of North Atlantic rifting.