Geometry of extensional faults developed at slow-spreading centres from seismic reflection data in the Central Atlantic (Canary Basin).

Reston, Timothy J., Ranero, César R., Ruoff, O., Perez-Gussinye, M. and Danobeitia, J.J. (2004) Geometry of extensional faults developed at slow-spreading centres from seismic reflection data in the Central Atlantic (Canary Basin). Open Access Geophysical Journal International, 159 . pp. 591-606. DOI 10.1111/j.1365-246X.2004.02444.x.

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We present depth images, from portions of profiles that are close to flow-lines, of Cretaceous oceanic crust in the eastern Central Atlantic. Compared with post-stack time migrations, the images illustrate the improvement resulting from the application of pre-stack depth migration. The images document the scale and geometry of normal faulting in oceanic crust formed over 25 Myr at a half-spreading rate of less than 10 mm yr−1, and the variation in extensional style with position within the spreading segment. Away from major fault zones (FZs), most faults are subplanar, dip more than 35°, are associated with moderate basement relief (0.2–1 km relief) and may penetrate to deep crustal levels. These faults could be related to the lifting of the lithosphere out of the median valley to the flanking mountains. Also observed away from FZs are gently dipping to subhorizontal reflections in the upper crust, which resemble detachment faults. In contrast, the inside corner crust is more rugged, with basement highs rising up to 2 km above the intervening basins. This larger-scale topography is associated with a different style of faulting: the depth images reveal gently dipping (<35°) faults that are rooted in the deep crust and that project to the ridgeward flank of the dome-shaped large basement highs (1–2 km vertical relief). The faults seem to continue as the ridge-facing flank of these highs and some may extend over the crest of the high to breakaways beyond. In this case, the domal highs that form the exhumed footwall to the faults can be described as oceanic core complexes. These controlling faults are up to 20 km long and have a heave of ∼10 km, sufficient to have accommodated up to 50 per cent extension and to have exhumed deep crustal and perhaps even mantle rocks. We suggest that similar faults can explain the structure and lithologies found at megamullion structures (oceanic core complexes) at inside corners near the present-day spreading ridge.

Document Type: Article
Keywords: mid-ocean ridges; normal faulting; oceanic crust; seafloor spreading; seismic structure
Research affiliation: OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-GDY Marine Geodynamics
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1111/j.1365-246X.2004.02444.x
ISSN: 0956-540X
Date Deposited: 10 Feb 2010 15:36
Last Modified: 17 Jul 2018 10:16

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