HR: 17:30h
AN: GP54A-07    [Abstracts]
TI: Reconstructing the kinematics of thrust sheet rotation in the Wyoming Salient: a paleomagnetic study of Triassic redbeds
AU: * Weil, A B
EM: aweil@brynmawr.edu
AF: Bryn Mawr College, Department of Geology 101 North Merion Ave., Bryn Mawr, PA 19010, United States
AU: Adolph, Y
EM: ayonkee@weber.edu
AF: Weber State University, Department of Geosciences 2507 University Circle, Ogden, UT 84408, United States
AU: Sussman, A
EM: spring@lanl.gov
AF: Los Alamos National Lab, Los Alamos National Lab, Los Alamos, NM 87545, United States
AB: Understanding the kinematics and mechanics of orogenic curvature are long standing questions within the structural geology and tectonics community. At the root of these questions is when and how orogens acquire curvature relative to protracted deformation histories. In an effort to describe the kinematic history of the Wyoming salient of the Sevier fold-thrust belt a collaborative effort is underway to determine the three main displacement field components (translation, rotation and strain). Paleomagnetic data are reported here from 164 sites collected from redbeds of the Triassic Ankareh Fm. from throughout the Wyoming salient. Sampled redbeds carry three distinct remanent magnetizations distinguished by field tests and magnetic behavior: 1) a recent viscous magnetization that is usually removed by 250° C, but is sometimes stable through typical hematite unblocking temperatures, 2) a Cretaceous chemical remagnetization (32 sites), and 3) a near-primary Triassic magnetization that is carried by hematite and is stable up to 680° C (92 sites). Site mean directions have a high degree of scatter from the reference Triassic and Cretaceous directions in both site declination and inclination, suggesting significant local rotation and tilt subsequent to magnetization acquisition. Palenspastic structural restoration of individual site means reveals local rotation, significant regional orogenic rotation, and differentiable thrust sheet rotation patterns that are all consistent with overall trends of structures found around the belt. Rotations are more pronounced in the northern and southern sections of the belt, near the intersection of the fold-thrust front with the Teton/Gros Ventre and Uinta Mountain uplifts. Statistical analysis of the rotations within and between individual thrust sheets suggests that between 70 and 80% of present-day curvature of the salient is secondary and must be accounted for in any kinematic model of thrust-belt evolution. Analysis of data for individual thrust sheets suggests an overall slightly greater component of secondary rotation within more interior thrust sheets. When combined with mesoscopic structure, strain, and thrust translation data, these results support a curvature model involving a combination of primary thickness variations in the sedimentary wedge, differential shortening to maintain orogenic wedge taper, and interaction with Laramide foreland uplifts.
DE: 1500 GEOMAGNETISM AND PALEOMAGNETISM
DE: 1525 Paleomagnetism applied to tectonics: regional, global
DE: 1527 Paleomagnetism applied to geologic processes
DE: 1533 Remagnetization
DE: 8100 TECTONOPHYSICS
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting