Abstract
A 3-D density anomaly model of the Irish Atlantic continental margin was generated from a regional inversion of the free air gravity data constrained by bathymetric and sediment thickness information. The model results are compared against a recent regional Moho structure compilation from velocity models from crustal-scale wide-angle reflection/refraction surveys. Using the inverted model, a regional map of Moho structure across the margin agrees well with the regional seismic compilation and also provides information in areas lacking deep seismic coverage. The density anomaly structure of the crust across the margin is investigated along model slices and using volume rendering of crustal layers. These views reveal extreme thinning,of the upper crust and a dominance of lower crustal densities in regions where exhumation of,serpentinized mantle has previously been interpreted. Using the regional view afforded by, the,inversion, the areal extent of these zones is tracked into regions lacking seismic constraints. Using the regional density anomaly model, variations in sediment thickness and crustal thickness are investigated to compute stretching factors across the margin and to identify zones,which deviate from local isostatic compensation. These zones generally correlate with faults,and rifting trends providing insights that could be useful for future palaeoreconstructions of North Atlantic rifting.
Highlights
The separation of Ireland and Newfoundland during the opening of the modern North Atlantic Ocean began in the Late Cretaceous (de Graciansky & Poag 1985; Tucholke et al 1989; Hopper et al 2006; Tucholke & Sibuet 2007) and has been interpreted by Doreet al. (1999) as an oblique re-opening of the Caledonian–Appalachian suture and fold system
A constrained 3-D gravity inversion of the free air data over the Irish Atlantic continental margin was undertaken and a regional density anomaly model was generated that is in agreement with constraints obtained from seismic and other methods
An independent proxy for Moho structure was obtained by defining a density anomaly isosurface and this information was combined with available sediment thickness estimates to enable the investigation of variations in upper, middle, lower and total crustal thickness as well as variations in the degree of extension across the margin
Summary
The separation of Ireland and Newfoundland during the opening of the modern North Atlantic Ocean began in the Late Cretaceous (de Graciansky & Poag 1985; Tucholke et al 1989; Hopper et al 2006; Tucholke & Sibuet 2007) and has been interpreted by Doreet al. (1999) as an oblique re-opening of the Caledonian–Appalachian suture and fold system. The separation of Ireland and Newfoundland during the opening of the modern North Atlantic Ocean began in the Late Cretaceous (de Graciansky & Poag 1985; Tucholke et al 1989; Hopper et al 2006; Tucholke & Sibuet 2007) and has been interpreted by Doreet al. (1999) as an oblique re-opening of the Caledonian–Appalachian suture and fold system This NE–SW striking suture and fold system developed due to the closing of the Iapetus Ocean in Palaeozoic time which stitched together the distinct basement terranes that make up the offshore Irish and Newfoundland margins (Haworth & Keen 1979; Williams 1984, 1995). The modern Irish Atlantic region (Fig. 2A) consists of a wide passive margin with a complicated tectonic history involving the overprinting of Late Palaeozoic to Cenozoic extension and inversion on the older basement terranes.
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