Detrital zircon geochronology and geochemistry of the rim gravels: a record of the Arizona-Plano and regional tectonics of the southwest U.S. cordillera

Forney, Rachel Caroline (2023) Detrital zircon geochronology and geochemistry of the rim gravels: a record of the Arizona-Plano and regional tectonics of the southwest U.S. cordillera. Masters thesis, Northern Arizona University.

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Abstract

The North American Cordillera spans from western Canada and continues into Mexico and includes a magmatic arc, fold and thrust belt, and foreland. However, questions remain as to where the fold and thrust belt of the ~150-45 Ma Sevier and Laramide orogenies continues south of Nevada to Mexico. Does the thrust belt continue along strike to Baja California, or did it angle to the southeast and continue into Arizona and southwestern New Mexico? Was the driving force of deformation flat slab subduction of the Farallon plate or the collision of a microcontinent? To better understand the southern section of the U.S. Cordillera, the sedimentology and zircon geochronology and geochemistry of a group of Late Cretaceous- Paleocene deposits termed the Rim Gravels were examined. Prior studies of the Rim Gravels suggest deposition occurred ca. 64-33 Ma. and deposits of basement gravels originated to the south and west of their current locations permitting interpretations of the presence of an area of high topography called the Mogollon Highlands or Arizona-Plano in southern Arizona before and during deposition. Studies of plutons in the region of the proposed highlands have yielded crustal thickness estimates between 48 km and 62 km, further supporting the continuation of an uplifted hinterland region across southern and central Arizona. New detrital zircon geochronology in addition to past detrital zircon and sanidine work constrains the provenance of the Rim Gravels to areas south of the Colorado Plateau based on 1.8-1.6 Ga grains characteristic of Yavapai and Mazatzal basement provinces and ~1.4 Ga emplaced Proterozoic plutons. Basement ages are accompanied by Jurassic and Cretaceous age zircons. Trace element geochemistry of zircon between 200 and 30 Ma was investigated to derive crustal thickness estimates in Arizona. These data indicate a crustal thinning event during Jurassic rifting of the Mexican Borderland Rift followed by a 145-101 Ma gap in magmatism, and an episode of crustal thickening to upwards of 63 km beginning at ca. 100 Ma prior to flat slab subduction of the Farallon plate.

Item Type:	Thesis (Masters)
Publisher’s Statement:	© Copyright is held by the author. Digital access to this material is made possible by the Cline Library, Northern Arizona University. Further transmission, reproduction or presentation of protected items is prohibited except with permission of the author.
Keywords:	Arizona-Plano; crustal thickness; geochemistry; Mogollon Highlands; Rim Gravels; Plate tectonics; New Mexico
Subjects:	Q Science > QE Geology
NAU Depositing Author Academic Status:	Student
Department/Unit:	Graduate College > Theses and Dissertations College of the Environment, Forestry, and Natural Sciences > School of Earth Sciences and Environmental Sustainability
Date Deposited:	09 Jul 2026 22:14
Last Modified:	09 Jul 2026 22:14
URI:	https://openknowledge.nau.edu/id/eprint/6290

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