28 Paleozoic Stratigraphy and Tectonics of the Southwestern Cordillera and Rocky Mountain Region

Wednesday, 16 March 2022
1:30 PM - 5:30 PM
CBC-A 112

STRUCTURAL ANALYSIS ALONG THE OURAY FAULT, SOUTHWESTERN COLORADO: IMPLICATIONS FOR THE KINEMATIC DEVELOPMENT OF THE LATE PALEOZOIC ANCESTRAL ROCKY MOUNTAINS

Paper number: 28-11
Program: Theme Sessions
Time: 4:45 PM – 5:05 PM

Authors

Abstract

The Ouray fault in southwest Colorado provides insight into the geometry and kinematics of deformation during the formation of the late Paleozoic Ancestral Rocky Mountains (ARM). The Ouray fault strikes WNW-ESE and dips subvertically to steeply south, juxtaposing the Paleoproterozoic Uncompahgre Group on the south side against Mississippian-Pennsylvanian strata on the north side. Kinematic data from the Ouray fault, adjacent small-scale faults, the observed offset, and folds in Paleozoic strata indicate that the Ouray fault records sinistral transpression. Using the average 15° W-plunging slickenlines from the principal slip plane, we estimate the total oblique sinistral displacement of the fault to be ~600 to 800 m. The uniformly overlapping Mesozoic strata atop the projected trace of the Ouray fault indicate that the fault is a preserved ARM structure not reactivated during the Laramide orogeny. The Ouray fault is oriented subparallel to the Uncompahgre Group bedding and follows the weaker Uncompahgre phyllite for most of its length, suggesting the preexisting structures within the Uncompahgre Group greatly influenced the orientation of the Ouray fault. N-S- to NW-SE-striking joints and quartz veins in all geologic units spanning the Paleoproterozoic to the Cenozoic postdate slip on the Ouray fault and likely formed during Cenozoic magmatism. A sample of calcite from the principal slip plane of the Ouray fault yielded a U-Pb date of 39.3 ± 6.2 Ma. We interpret this date to record resetting by late Eocene hydrothermal fluid flow. The record of strain around the Ouray fault may be representative of the southwestern margin of the Ancestral Uncompahgre uplift in Colorado. This study supports recent tectonic models for the ARM system which propose that ARM uplift was driven by NE-SW compression during the Pennsylvanian and Permian periods.

Geological Society of America Abstracts with Programs. Vol. 54, No. 2

doi: 10.1130/abs/2022CD-374299

© Copyright 2022 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.