FRACTURE HISTORY AND PALEOSTRESS TRAJECTORIES, CAMBRIAN FLATHEAD SANDSTONE, TETON RANGE, WYOMING USA

In the Teton Range, Middle Cambrian Flathead Formation sandstone contains folds associated with reverse faults and—in tabular dipping rocks and within folds—quartz lined opening-mode micro- and macroscopic fractures in five sets. Set A strikes north-south, B east-west, C northwest, D northeast, and E north-northwest to north-northeast. Heights are top bounded to hierarchical with A-B dips consistently bed normal. A-D are tilted and sheared in reverse fault-related folds. Sets are sequenced A→E using crossing relations. Set A is most abundant. CL colors suggest A may have two opening phases. Spatial arrangements are indistinguishable from random, regularly spaced fractal clusters or log-periodic clusters with inter-fracture distances for macroscopic fractures of c. 92.7 mm, markedly less than heights. Opening-displacement size distributions approximate power laws. Fracture strain is 0.00011 to 0.021. A-E quartz deposits contain fluid inclusion assemblages having minimum trapping temperatures ranging from 90 to 190°C clustering around 130-160 °C. Fluid inclusion temperatures and tilted quartz lined A-D fractures with open widths of 0.02 mm imply fracture during 66-44 Ma rapid uplift prior to emplacement of a west-directed Laramide reverse fault. A-B stretching could mark east-west shortening associated with uplift near the front of the Sevier thrust belt.