Principles of step-faulting are simulated in computer-synthesized and balanced structural cross sections of faulted and folded terranes. Isolation of geometry from mechanics and chronology allows a review of kinematics and chronology of deformation in layered rocks. Blind faults and duplex structures are geometric consequences of step-faulting, and are responsible for disparities in crustal shortening between superposed tectonostratigraphic units. These disparities are greatest in fold belts, which overlie belts of blind thrusts. Failure to recognize blind thrusts leads to incorrect estimates of both timing and amount of deformation. Geometric modeling demonstrates the intuitive nature of some widely accepted geologic assumptions. Geometric considerations alone suggest that faults and folds, which can be represented as products of faulting, form in response to a balance between differential tangential and vertical stresses. Where tangential stress provides the driving force, distribution of overburden load appears to control location of thrust ramps. Forward modeling by computer generates balanced cross sections at all stages of growth of a given structure, and shows that purportedly balanced cross sections may include impossible intermediate stages. Forward modeling also reveals geologic questions that must be answered before more sophisticated computer modeling programs can be written.
Following 25 years in petroleum and minerals exploration, Peter Jones founded International Tectonic Consultants Ltd. in 1980 as a geological consulting company specializing in exploration of areas of complex geological structure. Educated in Great Britain and the U.S.A., Dr. Jones has worked on deformed belts in Europe, Asia and the Americas. Author of more than 25 papers
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Exploration for petroleum requires much data, and the principles with which to interpret them. Because well and seismic data are extremely expensive in fold and thrust belts, application of simply geometric principles can multiply the effectiveness of geological and geophysical interpretations. Geometry of layerd rocks, expressed by maps, cross sections, and seismic profiles, is the basis for interpreting the geological structure. This publication contains 7 chapters covering thrust faults, generation of folds, and thrust and fold time and sequence from the geometric perspective.