13-9 Preliminary Kinematic Assessment of the Utah Sevier Thrust Belt: an Integrated Study using Anisotropy of Magnetic Susceptibility, Minor Structure, and Paleomagnetic Data

Session: Toe to Toe: Cordilleran Systems from Trench to Retroarc Domains

Presenting Author:

Authors:

Abstract:

The frontal portion of the classic thin-skinned Sevier fold-thrust belt in Utah displays varying curvature and lateral linkages from the Charleston-Nebo salient in the north, across the Lemmington transfer zone to the central Utah salient, to the Kanarra fold belt and Virgin anticline in the south near the Nevada border. Structural trends vary from N-S to NE-SW, with approximately 60° of map-view curvature. Importantly, during critical wedge growth, detachments along the leading edge of the belt interacted with thick-skinned Laramide structures along the margin of Colorado Plateau, which likely influenced the system final form and geometry.

To better understand kinematic evolution and curvature of this classic Sevier belt, structural (minor fault, cleavage/ tectonic stylolite orientations), anisotropy of magnetic susceptibility (AMS), and paleomagnetic data sets were collected from over 30 sites and integrated with previously published data sets. Early layer-parallel shortening (LPS) directions determined from minor faults and cleavage and from AMS fabrics were oriented ENE to SE, roughly perpendicular to local structural trends along the belt. A strike test for paleomagnetic data indicates that about 75% of curvature in the belt resulted from secondary vertical-axis rotations during thrust emplacement, with 25% of the curvature related to primary trend variability. While strike test results numerically resemble those of the Wyoming salient to the north, the Utah belt shows greater local geometric variability, interpreted to reflect along-strike variations in primary stratigraphic thicknesses and nature of evaporite-bearing detachments, plus interactions of frontal thrust sheets with local basement heterogeneities. The Laramide Uinta Mountains uplift to the north and Circle Cliffs and San Rafael uplifts in the Colorado Plateau to the east likely obstructed frontal thrust sheet transport and caused localized refraction and interaction of stress-strain directions between the Seiver and Laramide belts. These findings represent the first comprehensive regional analysis of shortening and vertical-axis rotations along the Utah Sevier belt and highlight how pre-existing crustal architecture influenced thrust belt development and curvature mechanisms.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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