Measurements of the extension required for crustal breakup on the magma-poor Iberia-Newfoundland conjugate margins

Rifted margins have been extensively studied, however there are still many important questions related to their formation processes. We use the Iberia-Newfoundland conjugate rifted margins as a natural laboratory to investigate how much extension is required to produce crustal rupture and separation. To achieve our aim we use; (i) gravity anomaly inversion to measure continental crustal thinning, (ii) subsidence analysis to measure continental lithosphere thinning and (iii) fault heave summation from seismic observations to obtain brittle continental crust extension. Integration of thinning from gravity anomaly inversion and subsidence analysis is used to determine continental crust extension and continental lithosphere extension respectively. These measurements have been made between the proximal continental crust and the distal Limit of Contiguous Continental Crust (LCCC) on the northern (SCREECH1 and ISE01) and the southern (SCREECH2 and TGS/LG12) conjugate seismic profiles. For the Iberia-Newfoundland conjugate rifted margins, extension values determined from the integration of crustal and lithosphere thinning are similar and suggest that on average 172 km of extension is required to produce crustal breakup. In contrast, measured extension from fault heave summation is on average 128 km which indicates an apparent extension discrepancy at the scale of the whole conjugate margin system when observed brittle continental crust extension is compared with lithosphere and crust extension.