HR: 1340h
AN: T33C-1479 [Abstracts]
TI: Where has all the strain gone? Mis-match between extension and contraction during gravity tectonics, SW Arican continental margin
AU: Lomas, K
EM: Kristian Lomas
AU: * Paton, D
EM: d.a.paton@leeds.ac.uk
AF: School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, United Kingdom
AU: Butler, R
EM: butler@earth.leeds.ac.uk
AF: School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, United Kingdom
AU: Morgan, R
EM: richardmorgan@sussexenergy.com
AF: Sussex Energy, Global House
1 Ashley Avenue, Epsom, KT18 5AD, United Kingdom
AB:
Many continental margins comprise coupled deformation of the sedimentary sequence with growth strata in the
near shore and toe-thrust compression in the distal portion Intrinsically, strain should balance between these
two domain such that compression equals extension, however, many reflection seismic studies suggest that
extension is greater than extension. Caution must be used in many of these examples because of poor imaging
of toe-thrust geometry, and hence, significant uncertainty in the calculated strain.
This study presents a 200 km long transect across the Namibian passive margin of the South Atlantic that
images over 4 km of Cretaceous and tertiary post-rift strata. The seismic data permit good matches across
faults and a low uncertainty in the geometric interpretation. These fault geometries derive robust line-length
restorations of the stratal reflectors. Nevertheless there is a significant discrepancy between the stratal
shortening (9km) in the toe thrust domain and the minimum layer extension (> 35km ) in the correlative updip
extensional domain. The role of distributed strain, out-of-plane motion and missing contraction (geometric
uncertainty) are explored in the context of the seismic dataset.
DE: 8005 Folds and folding
DE: 8010 Fractures and faults
DE: 8104 Continental margins: convergent
SC: Tectonophysics [T]
MN: 2007 Fall Meeting