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1 Department of Geology, University of Illinois, 1301 W Green Street, Urbana, Illinois 61801, USA
2 Illinois State Geological Survey, 615 E Peabody Drive, Champaign, Illinois 61820, USA
3 Department of Geology, Brigham Young University, P.O. Box 24606, Provo, Utah 84602, USA
The continental interior platform of the United States is that part of the North American craton where a thin veneer of Phanerozoic strata covers Precambrian crystalline basement. N- to NE-trending and W- to NW-trending fault zones, formed initially by Proterozoic/Cambrian rifting, break the crust of the platform into rectilinear blocks. These zones were reactivated during the Phanerozoic, most notably in the late Palaeozoic Ancestral Rockies event and the Mesozoic-Cenozoic Laramide orogeny — some remain active today. Dip-slip reactivation can be readily recognized in cross section by offset stratigraphic horizons and monoclinal fault-propagation folds. Strike-slip displacement is hard to document because of poor exposure. Though offset palaeochannels, horizontal slip lineations, and strain at fault bends locally demonstrate strike-slip offset, most reports of strike-slip movements for interior-platform faults are based on occurrence of map-view belts of en echelon faults and anticlines. Each belt overlies a basement-penetrating master fault, which typically splays upwards into a flower structure. In general, both strike-slip and dip-slip components of displacement occur in the same fault zone, so some belts of en echelon structures occur on the flanks of monoclinal folds. Thus, strike-slip displacement represents the lateral component of oblique fault reactivation; dip-slip and strike-slip components are the same order of magnitude (tens of metres to tens of kilometres). Effectively, faults with strike-slip components of displacement act as transfers accommodating jostling of rectilinear crustal blocks. In this context, the sense of slip on an individual strike-slip fault depends on block geometry, not necessarily on the trajectory of regional
1. Strike-slip faulting in the North American interior differs markedly from that of southern and central Eurasia, possibly because of a contrast in lithosphere strength. Weak Eurasia strained significantly during the Alpine-Himalayan collision, forcing crustal blocks to undergo significant lateral escape. The strong North American craton strained relatively little during collisional-convergent orogeny, so crustal blocks underwent relatively small displacements.
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  W. D. Cunningham and P. Mann Tectonics of strike-slip restraining and releasing bends Geological Society, London, Special Publications, 2007; 290: 1 - 12. [Full Text] [PDF]
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P. Mann Global catalogue, classification and tectonic origins of restraining- and releasing bends on active and ancient strike-slip fault systems Geological Society, London, Special Publications, 2007; 290: 13 - 142. [Abstract] [Full Text] [PDF]
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