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Modelling of Basin Inversion |
Mobil Research and Development Corporation, PO Box 650232, Dallas, TX 75265, USA
Physical models using wet clay show that, although both fold and fault geometries change with increasing amounts of inversion, it is difficult to estimate the magnitude of inversion. During extension, a listric main normal fault and a rollover fold cut by secondary normal faults developed above two diverging, basal plates. With 50 0nversion (4 cm extension, 2 cm shortening), the main normal fault underwent reverse displacement, and an asymmetric syncline formed in the pre-growth layers in the hangingwall. Secondary antithetic and synthetic normal faults passively rotated. Faults on the synclinal limb near the main normal fault rotated away from the fault, whereas those on the opposing limb rotated towards the fault. A broad anticline formed at shallow levels above the original half graben. Compressional reactivation of the main normal fault ceased between 50% and 100 0nversion (4 cm extension, 4 cm shortening). Instead, low-angle thrust faults with small displacements accommodated most shortening. The shallow anticline above the original half graben expanded laterally and vertically. With 200 0nversion (4 cm extension, 8 cm shortening), low-angle thrust faults with large displacements deformed the hangingwall and footwall of the main normal fault. Thrust faults cut the main normal fault and many of the secondary normal faults. The geometry of the hangingwall fold varied with depth. A broad anticline deformed the upper growth layers, changing to a syncline in the lower growth layers and an anticline in the pre-growth layers.
Estimates of inversion from null point analysis, amount of uplift above regional datum, or line length balancing, grossly underestimate the amount of shortening in the models. In addition, both the 50% and 100 0nversion models lack the large-scale deformation features typically associated with compression. These results suggest that both quantitative and qualitative techniques used to calculate inversion magnitude can significantly underestimate the amount of shortening. Furthermore, if the inversion uplift is eroded or if many small-scale deformation features are not imaged seismically, then inversion may go unrecognized.
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  M. Panien, S. J. H. Buiter, G. Schreurs, and O. A. Pfiffner Inversion of a symmetric basin: insights from a comparison between analogue and numerical experiments Geological Society, London, Special Publications, 2006; 253: 253 - 270. [Abstract] [PDF]
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J. A. Cartwright, C. Mansfield, and B. Trudgill The growth of normal faults by segment linkage Geological Society, London, Special Publications, 1996; 99: 163 - 177. [Abstract] [PDF]
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