REGIONAL SCALE ANCESTRAL ROCKY MOUNTAINS TECTONICS: RELATION TO ASSOCIATED PENNSYLVANIAN–PERMIAN SOUTHEASTERN AND SOUTHWESTERN BASINS AND PLATE MARGINS

The Ancestral Rocky Mountains (ARM) represent one of the least understood tectonic episodes of North American Phanerozoic geologic history. Most Pennsylvanian – Permian tectonic models are based on perceived far-field compressional stress transmitted from either the southwest or southeast plate boundaries. Our group at Northern Arizona University is conducting a regional study on the tectonic evolution of the ARM and its relationship to the plate boundaries to the southeast (west Texas) and southwest (northern Mexico to southern California). Our objective is to better understand and test conflicting models for ARM deformation in this stratigraphic system rich in natural resources. One new NAU late Paleozoic model for SW North America at the plate scale (Leary and others, this meeting) argues for a transpressional southwest (Mexican) margin from ~320–280 Ma followed by a subduction boundary. The various models suggest differing trends in the timing of uplift and basin subsidence across the region. We are gathering new thermochronologic and provenance data within synorogenic basin strata in order to expand upon existing and ongoing investigations of the enigmatic ARM tectonostratigraphic system. Here we present the initial results and sampling strategy for our study. Our main targets are the Paradox and Eagle basins of central Colorado, ARM basins in Utah and CO, and the extensive exposure of Pennsylvanian–Permian strata from southern NV through the transition zone of AZ to southern NM. Initial results suggest that the ARM basins and uplifts began synchronously in the Desmoinesian stage and received sediment from both local and extrabasinal sources. We also observe that regional sediment dispersal patterns may have been systematically influenced by paleoclimate and associated eustatic sea level variations.