T167 Late Cretaceous to Early Paleogene Tectonic Development of the North American Cordillera I

Tuesday, 24 September 2019
8:00 AM - 12:00 PM
Room 231ABC, North Building

THE ARIZONAPLANO: GEOCHEMICAL EVIDENCE FOR THICK CRUST DURING THE LARAMIDE OROGENY

Paper number: T167-6
Program: Technical Sessions
Time: 9:10 AM – 9:25 AM

Authors

Abstract

Previous studies of the central U.S. Cordillera have indicated a high-elevation orogenic plateau, the Nevadaplano, was present during the Late Cretaceous to Early Paleogene. The southern U.S. and northern Mexican Cordillera share a similar geologic history and many of the same tectonic features (e.g., metamorphic core complexes) as the central U.S. Cordillera, which raises the possibility that a similar plateau may have been present at lower latitudes. To test this hypothesis, we examined Laramide-age (80–40 Ma) continental arc geochemistry and employed an empirical relation between whole rock La/Yb and Moho depth as a proxy for crustal thickness. Calculations of crustal thickness from individual data points range between 45 and 72 km with an average of 57 ± 12 km (2σ) for the entire dataset, which corresponds to 3 ± 1.8 km paleoelevation assuming simple Airy isostasy. These crustal thickness and paleoaltimetry estimates are similar to previous estimates for the Nevadaplano and are interpreted to suggest that an analogous high-elevation plateau, the “Arizonaplano” may have been present in the southern U.S. Cordillera. The results raise questions about the geodynamic mechanisms that thickened the crust because shortening in the Sevier thrust belt is generally not thought to have extended south of ca. 35 °N latitude.

Geological Society of America Abstracts with Programs. Vol. 51, No. 5

doi: 10.1130/abs/2019AM-330985

© Copyright 2019 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.