Geometry and mechanisms of transverse faulting, Rocky Mountain Front Ranges, Canmore, Alberta
Although well documented from worldwide foreland belts, an actual mechanism for the formation of faults oriented at high angles to the predominant structural trend appears somewhat enigmatic. With this in mind, a system of Transverse faults contained within the major Rundle and Sulphur Mountain thrust sheets have been mapped in detail at a scale of 1:12,000. Structural observations at the 1) megascopic 2) mesoscopic and 3) microscopic scales were conducted in order to more accurately delineate relative timing and kinematics of the major deformational features. Shortening within the Rundle Thrust sheet has been accomplished by folding and imbricate thrusting whereas the Sulphur Mountain thrust sheet is deformed solely by the latter. Analysis of available field data suggests a progressive eastward advancing deformation, characterized by early thrusting in the Sulphur Mountain sheet, followed by folding and then thrusting in the Rundle sheet. The transverse fault system consists of a major fault which offsets the Sulphur Mountain Thrust and terminates at a major imbricate thrust of the Rundle Thrust sheet, as well as several minor transverse faults restricted to the individual thrust sheets. Analysis of palinspastic cross sections constructed for the time interval following folding but prior to thrusting, illustrates that the imbricate thrust steepened rapidly northwards in the immediate vicinity of the present location of the transverse fault. This geometry determines that northern strata wi1l be forced higher than southern counterparts during thrusting, thus resulting in a transverse fold and, with further displacement, a transverse fault. The initiation of transverse folding determines that the maximum shortening strain manifest by calcite and dolomite intragranular strains would rotate from an original position within the a-c tectonic plane to one within the b-c tectonic plane. Displacement along minor transverse faults has either occurred prior to the major faulting event, as demonstrated by one minor fault in the Sulphur Mountain thrust sheet, or contemporaneously with the major event as a response to extensional strain. Following the major faulting event, the two thrust sheets are essentially separated into two distinct structural domains. As lock up occurs along the lower thrust, further shortening within the sheet proceeds by sliding along pre-existing hanging wall thursts. Eventual erosion results in the deceptive appearance of structural discontinuity across the transverse fault zone.
Bibliography: p. 164-182.
Moffat, I. W. (1980). Geometry and mechanisms of transverse faulting, Rocky Mountain Front Ranges, Canmore, Alberta (Unpublished master's thesis). University of Calgary, Calgary, AB. doi:10.11575/PRISM/20284