--> Abstract: Extensional Fault Arrays in Strike-Slip and Transtension, by John W. F. Waldron; #90039 (2005)

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Extensional Fault Arrays in Strike-Slip and Transtension

John W. F. Waldron
University of Alberta, Edmonton, AB

Sedimentary basins developed under conditions of strike-slip or transtension are subject to significant rotational strains, yet faults developed in such regimes are commonly explained using simplified models related to states of stress, that ignore rotation. As deformation proceeds, faults undergo slip and fault-bounded blocks rotate; the heaves of extensional faults provide a means of quantifying this rotation. For ideal strike-slip (simple shear), the apparent stretch due to fault heaves can be related simply to shear strain. At shear strains (gamma) above 1.0, previously formed extensional faults begin to show inversion as reverse faults, becoming fully inverted when the shear strain reaches 2.0. In transtensional basins the angle of divergence (alpha) represents the relative importance of shear and extension and needs to be incorporated in the calculation. However, if the orientations of faults relative to the basin-bounding faults is measured, a relationship between fault heaves and amount of deformation can be derived.

In the Stellarton basin of Nova Scotia, Canada, fault heaves and orientations can be measured from subsurface mine plans, which provide unparalleled 3-dimensional control on basin geometry. Measurements of these quantities indicate that strain was only mildly transtensional, with a small (<10°) angle of divergence. The relationship between the degree of shearing and fault heave potentially provides assists the development of basin models wherever strike-slip or transtensional basins have been explored in detail by seismic or other subsurface methods.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005