Post-cretaceous structural geology near Del Norte Gap, Brewster County, Texas

The-west-dipping, north-northwest-trending Black Peak fault and associated monoclines which form the western flank of the Marathon dome, are well exposed near Del Norte Gap. Field mapping shows that the dip of the Black Peak fault increases downward from zero to 80 degrees. A northeast-trending right lateral fault cuts the hanging wall of the Black Peak fault at Del Norte Gap. The Black Peak fault has greater displacement south of the gap than north of the gap. Several north and northwest-trending normal faults cut the Cochran Mountains. The folding and faulting took place after the deposition of the upper Boquillas Limestone and before the deposition of Quaternary gravels. Vertical uplift of the Marathon dome during the Laramide orogeny produced the Black Peak fault and associated features. Normal faults later cut the area. The structural features near Del Norte Gap correspond well to previously described analytical and experimental configuration of features produced by differential vertical movement of basement blocks and previously described examples of vertical tectonics.