AN IMAGE LOG-BASED GEOMETRICAL AND TEXTURAL ANALYSIS OF A LOW-ANGLE NORMAL FAULT SYSTEM BENEATH THE F.O.R.G.E. SITE NEAR THE MINERAL MOUNTAINS, UTAH
Sub-horizontal basin strata at the top of the logged interval (2240 ft) increase in dip with depth to a mean orientation (dip/azimuth) of 15/297 (n = 47) over 2700-3150 ft. Rare faults and fractures in the basin dip 45-55° toward the E and W. At the basin-basement contact at 3176 ft is a strongly conductive feature of 0.5 ft in thickness, oriented 26/250. The only substantive low-angle, W-dipping planes are associated with cataclastic textures over 3176-3186 ft and 3212-3222 ft with mean orientations of 13/300 (n = 16) and 26/268 (n = 8), respectively. Basement fabrics define an elongated, W-E dome with no significant preferred orientation that would indicate top to the W shearing. In the basement (3176-7550 ft), faults have mean orientations of 51/270 (n = 35), 47/074 (n = 8), and 76/176 (n = 4). Cataclastic textures are prevalent over 3176-3410 ft, and are only locally developed deeper in the basement within 2-12 ft of fault planes. Conductive fractures have a range of orientations, but they dominantly dip W with a mean orientation of 39/276 (n = 1260), or are sub-parallel to faults with mean orientations of 74/183 (n = 220), 67/133 (n = 110), and 38/084 (n = 180).
Results indicate that the shallowly W-dipping seismic reflector encountered by the borehole is a LANF that primarily accommodated deformation via brittle deformation mechanisms. No obvious shear or mylonitic textures are obvious from the image log, or are too fine-grained to observe.