Plate kinematic modelling of the Atlantic and Arctic Oceans for conjugate margin studies

The Iberian and Newfoundland conjugate margins are undoubtedly some of the beststudied margins globally. Despite this, there is still very little consensus as to Iberia’s Mesozoic position during its early stages of divergence from North America. Inconsistencies in modelling early stages of plate divergence in this region stem from the extensive transition zones bordering the southern North Atlantic Ocean. Uncertainties in modelling the Iberian plate branch out of the region, making for more complex and questionable regional frameworks in which to interpret geological events in regions such as the Bay of Biscay or Pyrenees. Using three newly acquired seismic profiles from the southern Newfoundland Basin I assess the suitability of commonly used break-up markers (M-Series and J-Anomaly) for plate kinematic reconstructions. Interpretations suggest crustal structure at times coinciding with these breakup markers to comprise exhumed mantle with magmatic additions of an unknown age. Although the events from which these break-up markers originate immediately precede first seafloor spreading, they are neither instantaneous in time nor isochronous along the margin. Taking this analysis one step further, I derive potential seismic conjugates profiles using an already published seismic profile from the conjugate Tagus Abyssal Plain. Conjugate pairing shows there is little benefit as to a data versus model approach when deriving ‘conjugate’ profiles for the Iberia –Newfoundland margins. To work around the Iberia problem I propose the creation of a new, multi-plate circuit constraining the plates surrounding the smaller Iberian plate.To test and validate the plate circuit approach I close the Atlantic – Arctic plate circuit and test its outputs, the relative motions of the Greenland and North American platesagainst magnetic anomaly data of the Labrador Sea region. This model provides a regional context to study both divergent and convergent phases affect the SW Greenland margin with quantified uncertainties attached to the model. I go on to apply this proven plate circuit technique to the Iberia – Newfoundland problem. By generating three new plate circuits using the African, Moroccan, Iberian and North American plates I provide a statistically quantifiable context in which to study the evolution of plate boundaries along the northern and southern Iberian margins as well as in NW Africa. These findings provide rational as to modelling the earliest stages of divergence between Iberia and Newfoundland. <br/

3D development of detachment faulting during continental breakup

The developing asymmetry of rifting and continental breakup to form rifted margins has been much debated, as has the formation, mechanics and role of extensional detachments. Bespoke 3D seismic reflection data across the Galicia margin, west of Spain, image in unprecedented detail an asymmetric detachment (the S reflector). Mapping S in 3D reveals its surface is corrugated, proving that the overlying crustal blocks slipped on S surface during the rifting. Crucially, the 3D data show that the corrugations on S perfectly match the corrugations observed on the present-day block-bounding faults, demonstrating that S is a composite surface, comprising the juxtaposed rotated roots of block-bounding faults as in a rolling hinge system with each new fault propagation moving rifting oceanward; changes in the orientation of the corrugations record the same oceanward migration. However, in contrast to previous rolling hinge models, the slip of the crustal blocks on S occurred at angles as low as ∼20°, requiring that S was unusually weak, consistent with the hydration of the underlying mantle by seawater ingress following the embrittlement of the entire crust. As the crust only becomes entirely brittle once thinned to ∼10 km, the asymmetric S detachment and the hyper-extension of the continental crust only developed late in the rifting process, which is consistent with the observed development of asymmetry between conjugate magma poor margin pairs. The 3D volume allows analysis of the heaves and along strike architecture of the normal faults, whose planes laterally die or spatially link together, implying overlaps in faults activity during hyper-extension. Our results thus reveal for the first time the 3D mechanics and timing of detachment faulting growth, the relationship between the detachment and the network of block-bounding faults above it and the key processes controlling the asymmetrical development of conjugate rifted margins. Highlights • The 3D seismic data provide unprecedented details of the mechanisms of breakup. • S detachment is corrugated and made of root zones of successive normal faults. • S rooted steeply but continued to slip at low-angle (down to 20°). • Extensional faulting migrated oceanwards by sets of faults active concurrently. • The asymmetric detachment developed as the crust became entirely brittle