Faulting and diapirism above basement normal faults
- Univ. of Texas, Austin, TX (United States). Bureau of Economic Geology
The authors conducted two sets of scaled, tectonic experiments to investigate the effect of basement-involved extension on a sedimentary cover that includes a ductile lower part and a brittle upper part. Rigid plastic blocks with a 60[degree]-dipping precut plane represented an initially flat basement at the onset of faulting. A viscous silicone polymer simulated the lower, ductile cover. They chose dry sand as an analog for the upper brittle cover. The first set of experiments simulated deformation in a sediment-starved basin where deposition was absent or too slow to compensate for the vertical offset caused by displacement along basement faults. Viscous flow in the source layer from the upthrown block toward the downthrown block opposed the formation of large topographic relief. Regional extension was accommodated in the brittle upper cover by graben faulting above the upthrown block. Further extension triggered diapiric piercement through the faulted graben. In the second set of experiments, new sand layers were deposited during extension, leveling the top of the brittle upper cover above each side of the basement fault. This sedimentation reversed the sense of viscous flow in the lower viscous cover by (1) flattening topography, and (2) increased the thickness and weight of sediment above the downthrown block. An early graben formed in the uplifted block and rapidly evolved into a tall downbuilding diapiric wall. Both sets of experiments show that the presence of a low-viscosity layer effectively decouples the sedimentary cover from its basement. As long as the ductile layer is thick and of low viscosity, faults and diapirs can form far away from the basement fault. Faults and folds directly above the basement fault form only after the viscous layer has been depleted and the basement footwall indents the brittle upper cover.
- OSTI ID:
- 5935425
- Report Number(s):
- CONF-921058-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 24:7; Conference: 1992 annual meeting of the Geological Society of America (GSA), Cincinnati, OH (United States), 26-29 Oct 1992; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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