Mesoscopic analysis of folds in the Briggs Formation, Malone Mountains, Texas
Medford, Richard Malcolm
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The Malone Mountains are a group of ridges located approximately eleven miles west of the town of Sierra Blanca, Texas. The Briggs Formation, which is exposed in the Malone Mountains, contains highly distorted strata that include folds of different style and orientation as well as boudinage structures. The folds are of three scales. The largest scale occurs in competent carbonate members of the formation and in the overlying Malone and Torcer Formations. These folds trend to the north and northwest and have horizontal axes. Intermediate- and small-scale folds occur only in incompetent evaporite layers of the Briggs, where they exhibit a wide range of axial orientations that nonetheless define a great circle in stereonet projection. Distribution and asymmetries of the small-scale folds permit calculation of a separation angle of 16Â° and the derivation of a slipline direction trending N 44Â° E, directed upward at an angle of 49 Â°. Axial lanes of the large- scale folds and the surfaces of several thrust faults approximate the plane along which the intermediate- and small-scale folds are distributed. Thus, it appears that folding on all orientations, and thrusting are part of the same, perhaps protracted deformation. The sense of tectonic transport is the direction of the slip line.