HR: 1340h
AN: T53B-1307    [Abstracts]
TI: Deep-Towed Sidescan Sonar Studies of Amagmatic Spreading Centres: the Mid-Atlantic Ridge at 13N
AU: * Mallows, C
EM: christopher.mallows@dur.ac.uk
AF: Durham University, Dept. Of Earth Sciences Science Labs, Durham, DH13LE, United Kingdom
AU: Searle, R C
EM: r.c.searle@dur.ac.uk
AF: Durham University, Dept. Of Earth Sciences Science Labs, Durham, DH13LE, United Kingdom
AU: Party, J S
EM: christopher.mallows@dur.ac.uk
AB: In areas of sparse magmatism, plate separation is accommodated predominately by tectonic processes, which is often observed in the form of long-lived detachment faults exhuming lower crustal rocks and mantle peridotites to the seafloor. During research cruise JC007, a number of these oceanic core complexes (OCCs) recently identified by Smith et al. (2006) along the Mid-Atlantic Ridge (MAR) were imaged using the National Oceanography Centres Towed Ocean Bottom Instrument (TOBI). Sidescan sonar data were collected across two active OCCs at 1320N and 1330N and one inactive OCC at 1350N, including the intervening regions. We made extensive use of 3-D Fledermaus visualisations during our interpretations, and will include these in our presentation. The sidescan sonar data show distinct similarities between the two active OCCs. They both appear as large domal detachment surfaces being exhumed from beneath the ridge axis that are capped by a complexly deformed central massif and volcanic ridge at the breakaway (as suggested by Smith et al, 2006). The structures extend for c.20km off axis and c.10km along axis, and the detachment faults are characterised by large-scale spreading-parallel bathymetric corrugations and fine scale striations (interpreted as streams of basalt derived from tectonic erosional screes imaged at the terminations). The hanging walls above the zones of emergence of the detachment faults exhibit faulting that appears to trend from the ridge axis (N and S of the OCC) towards the spreading direction (at the OCC). The neo-volcanic zones along the ridge axis are apparently absent opposite active OCC formation, which is likely indicative of predominately tectonic spreading. In the regions between the active OCCs, sidescan sonar imagery shows a clear neo-volcanic zone at the ridge axis, indicating robust magmatic plate separation and accretion. The extinct OCC is characterised by heavy sediment cover over a much shallower detachment surface, presumably due to rotation and subsequent termination of the footwall. References Smith, D.K., Cann, J.R. & Escartin, J. Widespread active detachment faulting and core complex formation near 13N on the Mid-Atlantic Ridge, Nature, v.442/27, p.440-443, 2006.
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 8118 Dynamics and mechanics of faulting (8004)
DE: 8178 Tectonics and magmatism
DE: 8199 General or miscellaneous
SC: Tectonophysics [T]
MN: 2007 Fall Meeting