Calculation of shortening due to outcrop-scale deformation and its relation to regional deformation patterns

The objectives of this study are to: (1) assess the regional contribution of outcrop-scale structures in well exposed rocks of tectonic province; and (2) evaluate how failure to measure this scale of structure affects the assessment of regional deformation. The contribution of outcrop-scale structures to regional deformation has not been quantified because of the requirement of long continuous exposures to characterize and quantify the structures. This study used 18.6 km of semi-continuous roadcut and streambed exposures in well-exposed Devonian clastic rocks to construct 1:200-scale profiles to address this issue. The key results are: (1) outcrop-scale structures contribute about ⅙ to ¼ of the total regional shortening. (2) The submap-scale shortening components from microscale and outcrop-scale structures equal the map-scale shortening that would be interpreted from a regional cross section. Therefore, the submap-scale structures are important to the regional analysis of deformation. (3) The analysis was performed in the roof sequence of a blind thrust belt, where examination of the smaller structures shows that roof-sequence deformation preceded and continued through duplex formation. (4) The kinematic response of the roof sequence would be incorrectly identified as backthrusting if the shortening contribution of the outcrop-scale structures is ignored. (5) Although the measured outcrop-scale shortening does not match that predicted by fractal analysis of other workers, the fractal approach may still be valid.