RECONSTRUCTING MOAB FAULT KINEMATICS: JURASSIC, LARAMIDE, AND POST-LARAMIDE OFFSET

In the SW corner of Arches National Park (ANP), the Moab Fault has become an exemplar of normal fault deformation (Foxford et al, 1996; Doelling et al, 2002; Sollum et al, 2005; 2010; Davatzes et al, 2005; Hodson et al, 2016). In ANP, the Moab Fault shows just over 1000 m offset. The fault is detached above the Paradox salt and is commonly inferred to have a listric trajectory to explain the prominent Moab anticline in its hangingwall. These outcrops are located at the N-plunging end (~7º) of the Spanish Valley salt wall. From the Colorado River south, the flat floor of Spanish Valley exposes the caprock crest in the core of the salt wall anticline. The Moab Fault has been interpreted to have continued to the south along the full extent of Spanish Valley, although the strata containing the fault is now eroded away. Diapiric deformation into salt walls occurred in the Paradox Basin associated with the Late Penn-Permian uplift of the Uncompahgre contractional fault block (Ancestral Rocky Mountains). Recent Paradox Basin structural restorations document the growth of the salt diapirs, but the youngest datum is Jurassic. Cretaceous and Tertiary structural history recording Moab Fault offsets has been unexamined. This study presents sequential structural restorations for 4 structural profiles: two situated north of Moab across the SW corner of ANP, one across the northern edge of the Moab townsite, and one just south of Moab. Portions of these profiles were initially constructed by Doelling (M181 A, B, C; M260 A). Restoration to a mid-Jurassic datum is straightforward, but younger datums requires an estimated reconstruction of sedimentary units lost during Laramide contractional uplift (minor) and Late Tertiary uplift of the Colorado Plateau (major). To that end, my sequential restoration of the Moab Fault includes: 1) a mid-Jurassic datum, 2) an earlier Paleogene datum (following Laramide contraction), 3) a later Paleogene (?) datum (following post-Laramide extension), and 4) present-day structural profile beneath current topography. If my stratigraphic reconstructions are correct, majority of salt wall structural relief is in place by mid-Jurassic, a small amplification of the salt anticline occurs in the Laramide, and a large majority of Moab Fault offset occurs via post-Laramide extensional reactive diapirism (heave ~500 m).