HR: 0830h
AN: GP41C-0055    [PDF]
TI: Paleomagnetic Vertical Axis Rotations Caused by Oblique Deformation Within the Grand Hogback Monocline, Colorado Plateau
AU: * Tetreault, J L
EM: joya@cires.colorado.edu
AF: Dept. Geosci., Univ. Colorado, CB 399, Boulder, CO 80309-0399 United States
AU: Jones, C H
EM: cjones@cires.colorado.edu
AF: Dept. Geosci., Univ. Colorado, CB 399, Boulder, CO 80309-0399 United States
AU: Boyle, B
AF: Dept. Geosci., Univ. Colorado, CB 399, Boulder, CO 80309-0399 United States
AB: The monoclines of the Colorado Plateau, formed over reactivated Precambrian faults during the Laramide Orogen, locally absorb oblique deformation (e.g. Tinsdall and Davis, 1999; Bump and Davis, 2003). Thus it can be assumed that the distributed deformation in the overlying, folded strata from oblique slip would be in the form of a strike-slip shear zone with some unknown amount of vertical axis rotation. Paleomagnetic vertical axis rotations in the monoclines of the Colorado Plateau can constrain such a rotation from strike-slip motion on the underlying thrust-faults. This study focuses on new paleomagnetic work performed on the anticlinal hinges of the San Rafael monocline, central Utah, and the Grand Hogback monocline, Colorado. The San Rafael monocline is a large, curvilinear structure with oblique deformation from right lateral slip proposed on the southern, northeast-southwest oriented limb (Bump and Davis, 2003). The Grand Hogback monocline is a large, highly sinuous feature, with left-lateral strike-slip deformation proposed along the central, east-west oriented limb (Murray, 1966). Three sites sampled within the anticlinal hinge of the north and south limbs of the San Rafael monocline, yielded no vertical-axis rotations. Two sites were sampled along the northern, north-south oriented limb and the central limb of the Grand Hogback monocline. A minimum rotation of -15$\deg$ $\pm$ 8$\deg$ was determined from Upper Triassic strata sampled on the anticlinal hinge of the central limb (39.5 N, 107.4 W). The tilt-corrected direction for this site is D = -23.6$\deg$, I = 24.3$\deg$, $\alpha$ $_{95}$ = 9.6$\deg$, N = 16. Correlative strata sampled on the north limb (39.8 N, 107.9 W) contain a clockwise rotation of 8.8$\deg$ $\pm$ 4.5$\deg$. This paleomagnetic result provides a minimum constraint of 23$\deg$ of differential tectonic rotation absorbed in this Laramide structure. Further work in the overlying pre-Laramide strata will provide further information on the amount and distribution of rotation, and thus constrain the mechanism of deformation for the Grand Hogback monocline. The presence of rotations at this monocline and the absence of rotations on the San Rafael monocline must be further investigated to understand how the Laramide Orogen formed the monoclines of the Colorado Plateau.
DE: 1525 Paleomagnetism applied to tectonics (regional, global)
DE: 1527 Paleomagnetism applied to geologic processes
DE: 1744 Tectonophysics
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting