T145 Oblique Motion on the North American Cordilleran Margin II: Jurassic to Paleogene

Monday, 23 September 2024
1:30 PM - 5:30 PM
304B

REGIONAL EXHUMATION OF THE LARAMIDE

Paper number: T145-9
Program: Technical Sessions
Time: 3:25 PM – 3:40 PM

Authors

Abstract

Western North America is a Cordillera-type orogenic system that preserves a Mesozoic to Cenozoic record of subduction related processes. However, there remain major questions about the mechanism and timing of flat-slab subduction, trajectory of the flat-slab, coupling mechanism(s), and the upperplate deformational response. Central to the flat-slab hypotheses are the timing, rate, and distribution of exhumation experienced by the Laramide uplifts as recorded by low-temperature thermochronology. In this contribution, we address the timing of regional exhumation of Laramide uplifts by combining apatite fission-track (AFT) and (U-Th-Sm)/He (AHe) data from 21 new samples with 564 published AFT, AHe, and zircon (U-Th)/He ages from documented Laramide structures in Arizona, Utah, Wyoming, Colorado, Montana, and South Dakota. We integrate our results with existing geological constraints on the timing of uplift and with new regional cross-sections to reconstruct the spatial and temporal history of Laramide exhumation from the mid-Cretaceous to Paleogene. Our analysis suggests a two-stage exhumation of the Laramide province, with an early phase of localized exhumation occurring at ~100 - 80 Ma in Wyoming and Montana, followed by a more regional period of exhumation at ~70 - 50 Ma. Generally, the onset of enhanced exhumation occurs earlier in the northern Laramide province (~90 Ma) and later in the southern Laramide province (~80 Ma). Thermal history models of selected samples along cross-sections through the Colorado Plateau and Wyoming-South Dakota show that regional exhumation occurred contemporaneously with deformation. We suggest that Laramide basement block exhumation is indicative of synchronous deformation propagating through end-loading as opposed to basal shear. These results have implications for testing proposed migration pathway models of Farallon flat-slab, alternative models such as terrane collision, and for how upper-plate deformation is expressed in flat-slab subduction zones globally

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-402757

© Copyright 2024 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.