HR: 17:00h
AN: T34B-05 INVITED     [Abstracts]
TI: Detachment Faulting Within Slow-Spreading Segments - Beyond the Corrugated Surface.
AU: * Reston, T J
EM: treston@ifm-geomar.de
AF: IFM-GEOMAR, Wischhofstrasse 1-3, Kiel, D24148 Germany
AU: Ranero, C R
EM: cranero@ifm-geomar.de
AF: IFM-GEOMAR, Wischhofstrasse 1-3, Kiel, D24148 Germany
AB: Acoustic mapping of slow-spreading ridges has revealed that some but not all inside corner massifs are topped by corrugated surfaces. These surfaces are interpreted as the exhumed slip surface of large offset normal faults. As with all faults, the extent of fault exposure in the transport direction represents a minimum estimate of the displacement along the fault. However, whereas most normal faults have displacements that are only a fraction of their along-strike extent to maintain strain compatibility, the corrugated surfaces are commonly close to equidimensional and in some cases are longer in the displacement direction. In some cases the corrugated surface is terminated laterally by transform or other structures (e.g. the Ascension transform - studied during Meteor cruise 62-4, October 2004), but in others no such clear truncation can be observed, causing potential strain compatibility problems. One solution is that the corrugated surface does not represent the full along strike length of the faults. Seismic images of Cretaceous oceanic crust image at inside corners detachment faults that follow top basement and image elsewhere detachment faults buried beneath a layer of fault blocks. We suggest that these apparently different types of detachment may be different parts of one type, i.e. that the corrugated surfaces continue along strike toward the segment middle beneath a layer of small fault blocks. This is consistent with observations made from bathymetric mapping at the current spreading center. The varying exposure of the detachment fault can be explained by a rolling hinge model in which the flexing fault becomes inactive either after it has been exhumed, or in the sub-surface. The former results in the exposure of the footwall as a corrugated surface, the latter requires new faults to cut up through the hangingwall and transfer fault slices to the footwall. As a result, the footwall is buried beneath a layer of such fault slices. We suggest that the variation in the depth at which the fault becomes inactive is controlled by the along segment variation in both lithospheric structure and the rheology of the fault zones. The model also explains why not all inside corner massifs exhibit corrugated surfaces: the exposure of such a surface relies not only on the development of an appropriate fault system, but also on the exhumation of the footwall of the fault. Another implication is that detachment faulting may be important along much of some spreading segments and that tectonic strain may be more important at segment centers than previously suggested.
DE: 3035 Midocean ridge processes
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 8004 Dynamics and mechanics of faulting (8118)
DE: 8416 Mid-oceanic ridge processes (1032, 3614)
SC: Tectonophysics [T]
MN: Fall Meeting 2005