3D development of detachment faulting during continental breakup

Abstract

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

Origin of Serpentinization Patterns Beneath the S‐Reflector Detachment Fault in the Galicia Margin, Offshore Spain

“…The alignment of the distribution of serpentinization beneath the S‐reflector with the paleotemperatures estimated at the end of rifting further supports this interpretation. This interpretation differs from previous models, wherein serpentinization is assumed to have facilitated slip on the S‐reflector detachment, and therefore occurred synkinematically (e.g., Lymer et al, ; Pérez‐Gussinyé & Reston, ; Reston et al, ).…”

“…It is unclear if the detected patterns extend more broadly across the 3‐D surface. Newly acquired seismic reflection data reveal the 3‐D nature of the fault zone and fault blocks overlying the detachment (Lymer et al, ; Schuba et al, ), suggesting that variations in serpentinization may also be more complex than what is imaged by 2‐D data.…”

Bouguer anomalies of the NW Iberian continental margin and the adjacent abyssal plains

“…Druet et al, 2018 and references therein); (3) the named Deep Galicia Margin, where hyperextension and mantle exhumation occur (e.g. Whitmarsh, White, et al, 1996;Lymer et al, 2019); (4) a marginal platforms region to the northwest of Galicia, resulting from the tectonic inversion of former half-graben basins (Druet et al, 2018;Murillas et al, 1990); (5) the Iberia abyssal plain, surrounding the margin to the west, and (6) the Biscay abyssal plain, to the north and northwest. These deformation domains are related to different crustal thickness and crustal type distribution, having distinctive gravimetric signal along the margin (Druet et al, 2018).…”

The role of serpentinization and magmatism in the formation of decoupling interfaces at magma-poor rifted margins

“…On reflection seismic sections, normal faults often seem to interact with intrabasement decoupling interfaces that generally appear as strong reflections. A well-studied example is the S-reflector, located at the base of hyperextended continental crust of the Galicia rifted margin (Sibuet, 1992;Reston, 1996;Whitmarsh et al, 1996;Reston and Pérez-Gussinyé, 2007;Reston, 2009;Lymer et al 2019). The S-reflector is commonly interpreted as a decollement due to the presence of a sole of serpentinized mantle, suggesting that hydration processes can control the structural evolution of hyperextended and exhumed mantle domains (Pérez-Gussinyé and ; Bayrakci et al, 2016).…”