Experimental modeling of salt flow subparallel to basement-involved faults
Creators: name: Needle, Mattathias David
Publisher: name: No Publisher Supplied
Year: 2016

description: Rock salt exhibits highly ductile behavior at shallow crustal levels, and its presence profoundly affects the structural development of rift basins. Basement-involved normal faults strongly influence the initial thickness and distribution of the synrift salt. Subsequent deformation and deposition during and after rifting cause the salt to flow. This work uses experimental (analog) modeling to examine the secondary structures that develop in the sedimentary cover above synrift salt that flows subparallel to the strike of basement-involved faults. In the models, silicone polymer simulates salt, wet clay simulates the sedimentary cover, and rigid blocks represents basement-involved faults. Extension imposed at the base of the models causes the silicone polymer to flow subparallel to the rigid blocks.  The models indicate that two zones of deformation form within the sedimentary cover: 1) a shear zone with oblique-slip faults that trends (sub)parallel to the strike of the underlying faults; and 2) an extensional domain with predominantly normal faults that strike (sub)perpendicular to the flow direction of the ductile unit. At the clay surface, some faults in the shear zone and extensional domain link, forming curved fault surfaces.  The initial thickness and distribution of the highly ductile unit affect the development of secondary structures in the overlying cover. The thickness of the ductile unit controls the degree of decoupling between shallow and deep structures. Where the ductile unit is thick, the extensional domain and shear zone in the cover are broad, whereas where the ductile unit is thin, the extensional domain and shear zone in the cover are narrow and form directly above the deep structures. Varying the initial distribution of the ductile unit produces subsequent asymmetrical deformation in the overlying cover.  The orientation of pre-existing faults, relative to the flow direction of the highly ductile unit, also has an influence on the development of secondary structures. When the flow of the ductile unit (relative to a pre-existing fault) produces highly oblique extension at depth, deformation is distributed broadly in the extensional domain, and the shear zone forms above and trends parallel to the pre-existing fault. However, when the flow of the ductile unit (relative to the pre-existing fault) produces highly oblique shortening at depth, 1) the trend of the shear zone in the cover is not parallel to the strike of the underlying pre-existing fault, and 2) secondary features in the extensional domain are muted in the cover. The latter suggests that the ductile unit distributes the deformation and, thus, subdues the expression of both shortening and extensional features at the surface.   Comparisons of the modeling results in this thesis to the deformation in the Jeanne dâ€™Arc basin of offshore Newfoundland, Canada, suggest that the synrift Argo Salt flowed parallel to the basinâ€™s long-axis. The salt flow produced secondary structures in the sedimentary cover above the salt including trans-basin normal faults and shear zones above basement-involved faults.     â€ƒ