WHAT LIES BENEATH: THE STORY OF THE FAULTS AND FRACTURES OF THE HOGBACK MONOCLINE

The formation of monoclines in a 2D cross section view is well understood; however, map-view bends present on some monoclines and their 3D evolution have not been addressed. This study uses analogue modeling to investigate the deformation in a monocline bend, including the development of fractures. The result of this modeling can be compared to bend geometry and fracture patterns such as those found on the Hogback monocline west of Farmington, NM.

In this study, the analogue model creates reverse slip on a single basement fault with an s-shaped bend in it. The basement deforms an overlying wet clay layer, scaled in size and strength to represent typical Colorado Plateau strata. Three separate models were tested to represent three different shortening directions: one normal to the straight segments of the fault at 330˚ azimuth shortening, one at 360˚ azimuth, and one at 300˚ azimuth. Fractures formed on the clay surface with patterns varying due to shortening direction. In the 330˚ model, most of the fractures formed parallel to the strike of bedding at the crest of the monocline. The 360˚ model had fracture patterns that were oblique to the crest of the monocline at about a +30˚ from strike. The 300˚ model had fractures that were also oblique to the crest of the monocline and tended to strike -30˚ from strike.

Fractures along a bend in the Hogback monocline were measured in a previous study. Preliminary results of our analogue modeling suggest that shortening responsible for the Hogback monocline was oblique at 360˚. Constraints on oblique shortening have implications for kinematics of Laramide tectonics in northwest New Mexico.