Modelling hanging wall accommodation above rigid thrust ramps

Modelling hanging wall accommodation above rigid thrust ramps Experimental models are used to study the role of material rheology in hanging wall accommodation above rigid flat–ramp–flat thrust footwalls. The deformation in the hanging wall was accomplished by forwards sliding along a rigid basal staircase trajectory with a variable ramp angle, α , ranging from 15° to 60°. We model different ramp angles to examine hanging wall accommodation styles above thrust ramps of overthrust faults ( α ranging from 15° to 30°), as well as above pre-existing normal faults ( α ranging from 45° to 60°). For the hanging walls we used stratified frictional (sand) and viscous (silicone putty) materials. In this paper we study three types of models. Type 1 models represent purely frictional hanging walls where accommodation above thrust ramps was by layer-parallel thickening and by generating a series of back thrusts. Type 2 and 3 models represent stratified frictional/viscous hanging walls. In these models, accommodation was by a complex association of reverse and normal faults, mainly controlled by the rheological anisotropy as well as by the ramp inclination angle α . In Type 2 models the silicone covered only the lower flat, while in Type 3 models it also covered the rigid ramp. For α ≤30° in Type 2 models and α ≤45° in Type 3 models, the viscous layer inhibited the development of back thrusts in the frictional hanging wall, instead the silicone thickened to develop a ‘ductile ramp’. For α -values higher than 30° in Type 2 models and α =45° in Type 3 models, back thrusts develop in response to the bulk compression. The experiments simulate many structures observed above natural thrust ramps with α ≤30° and pre-existing normal faults with α ≥45°. The models emphasise the importance of a basal ductile layer, which allows the hanging wall to step-up over the rigid ramp by building up its own ductile ramp. The models also emphasise that foreland-directed normal faulting can develop at a thrust front in the case that the vertical stress due to gravity exceeds the horizontal stress due to end-loading within a thrust wedge. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Structural Geology Elsevier

Modelling hanging wall accommodation above rigid thrust ramps

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Publisher
Elsevier
Copyright
Copyright © 2000 Elsevier Science Ltd
ISSN
0191-8141
eISSN
1873-1201
DOI
10.1016/S0191-8141(00)00033-X
Publisher site
See Article on Publisher Site

Abstract

Experimental models are used to study the role of material rheology in hanging wall accommodation above rigid flat–ramp–flat thrust footwalls. The deformation in the hanging wall was accomplished by forwards sliding along a rigid basal staircase trajectory with a variable ramp angle, α , ranging from 15° to 60°. We model different ramp angles to examine hanging wall accommodation styles above thrust ramps of overthrust faults ( α ranging from 15° to 30°), as well as above pre-existing normal faults ( α ranging from 45° to 60°). For the hanging walls we used stratified frictional (sand) and viscous (silicone putty) materials. In this paper we study three types of models. Type 1 models represent purely frictional hanging walls where accommodation above thrust ramps was by layer-parallel thickening and by generating a series of back thrusts. Type 2 and 3 models represent stratified frictional/viscous hanging walls. In these models, accommodation was by a complex association of reverse and normal faults, mainly controlled by the rheological anisotropy as well as by the ramp inclination angle α . In Type 2 models the silicone covered only the lower flat, while in Type 3 models it also covered the rigid ramp. For α ≤30° in Type 2 models and α ≤45° in Type 3 models, the viscous layer inhibited the development of back thrusts in the frictional hanging wall, instead the silicone thickened to develop a ‘ductile ramp’. For α -values higher than 30° in Type 2 models and α =45° in Type 3 models, back thrusts develop in response to the bulk compression. The experiments simulate many structures observed above natural thrust ramps with α ≤30° and pre-existing normal faults with α ≥45°. The models emphasise the importance of a basal ductile layer, which allows the hanging wall to step-up over the rigid ramp by building up its own ductile ramp. The models also emphasise that foreland-directed normal faulting can develop at a thrust front in the case that the vertical stress due to gravity exceeds the horizontal stress due to end-loading within a thrust wedge.

Journal

Journal of Structural GeologyElsevier

Published: Aug 1, 2000

References

  • The inception and early evolution of the North Alpine foreland basin, Switzerland
    Allen, P.A; Crampton, S.L; Sinclair, H.D
  • Emplacement of foreland thrust systems
    Cello, G; Nur, A
  • The influence of pre-existing thrust faults on normal fault geometry in nature and in experiments
    Faccenna, C; Nalpas, T; Brun, J.P; Davy, P; Bosi, V
  • Structural analysis and interpretation of the surface deformation of El Asnam earthquake of October 10, 1980
    Philip, H; Meghraoui, M
  • Ancient synsedimentary structural control on thrust ramp development: an example from the Northern Apennines, Italy
    Tavarnelli, E

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