PALEOSTRESS/ STRAIN AND ROTATION PATTERNS ACROSS PARTS OF THE COLORADO PLATEAU AND UINTA ARCH: PRELIMINARY RESULTS OF STRUCTURAL, PALEOMAGNETIC, AND ANISOTROPY OF MAGNETIC SUSCEPTIBILITY STUDIES FROM MULTIPLE STRATIGRAPHIC LEVELS

Preliminary results are presented for integrated paleomagnetic and anisotropy of magnetic susceptibility (AMS) studies and kinematic analysis of minor structures from multiple Triassic, Jurassic, and Cretaceous stratigraphic levels across parts of the Colorado Plateau and Uinta arch, spanning Utah to southern Wyoming. Minor faults, best developed in limestone and conglomeratic sandstone layers, include widespread conjugate wedge faults that accommodated limited (<5%) early layer-parallel shortening (LPS) and display consistent relations relative to bedding around large-scale folds. Locally developed tectonic stylolites and rare vein arrays also accommodated limited LPS and rare tangential extension. Paleostress/ strain directions estimated from minor structures vary with location and structural trend of basement-cored arches/ monoclines, ranging from overall SW-NE to NW-SE for more NW to NE trending arches. Paleostress/ strain directions also partly refract with map-view curvature of individual arches. Minor fault kinematics record constructional strain with a component of tangential shortening at many sites, consistent with development of multiple trending arches and interaction of Sevier and Laramide stress fields along the western part of the plateau. Core samples collected from red beds are currently being analyzed to determine AMS fabrics, which have been shown to record subtle LPS fabrics in other parts of the Laramide foreland, and to determine remnant magnetization, which will be used to quantify vertical axis rotations.

Results of this study are combined with prior studies across the Laramide belt of Wyoming to test models of foreland deformation and flat-slab subduction. Very limited large-scale shortening across much of the Colorado Plateau may reflect a combination of weaker, hydrated mantle lithosphere that was sheared off resulting is less basal coupling, or stronger, more rigid lower crust with shortening only along variably oriented basement weaknesses and inherited fault zones. Complex paleostress/ strain patterns along the plateau margins may reflect interaction with the Sevier belt to the west and buttressing and interaction with Neoproterozoic faults to the north.