REGIONAL PATTERN OF MESOZOIC STRUCTURES IN THE CONFUSION RANGE, WESTERNMOST CENTRAL UTAH

Most of the Confusion Range (CR) was affected by only minor (< ca. 25 degrees) tilt, caused by Tertiary listric faults subsidiary to the east-rooted “Snake Range-Deep Creek Range [detachment] fault system” of E.L. Miller el al. (1999). In contrast, the Conger Range--the southwest part of the larger CR--is a distinct domain of large (>90 degrees) Tertiary tilt. Restoring these tilts, and building on the detailed mapping of a large part of the CR during the 1950’s and 60’s by R.K. Hose and coworkers, results in a coherent pattern of Mesozoic structures in the range. This pattern is like that about 100 km farther northwest in the southern Goshute Range of eastern Nevada (Silberling and Nichols, 2002), suggesting that it is regionally applicable. D1, which in the Goshute Range is associated with emplacement of the ca. 160 Ma White Horse pluton, produced attenuation faults at the pre-deformation crustal level of the Mississippian in both the Goshute and Confusion ranges. The extensive, attenuational, folded “décollements” envisaged by Hose (1976) within the Permian and Mississippian sections in the CR, however, are erroneous extrapolations of local D2 and D3 thrust faults. D2 resulted in conspicuous, kilometric-scale, more of less north-trending folds and east-directed thrust faults, such as the Salt Marsh thrust (Herring et al., 1998). Part of the upper plate of this thrust crops out at the northwest edge of the CR, the thrust is recognized seismically in the subsurface of Snake Valley to the west of the CR, and it may also be exposed in the Conger Range. A strain gradient, whereby D2 folds become tighter, more east vergent, and more overturned from east to west within the CR, suggests (a) major unexposed D2 thrust(s) like the Salt Marsh thrust may exist(s) to the west of the CR for its entire length. D1 and D2 structures are locally deformed by D3 folds and thrust faults that trend northeast and in the CR verge southeast. D2 and D3 may be shallow-level expressions of the generally east-directed metamorphic shear fabrics related to ca. 100-75 Ma plutonism in the footwall of the Tertiary Snake-Deep Creek detachment-fault system (E.L. Miller et al., 1988) and hence of the Sevier thrust-belt hinterland.