Earth and Planetary Sciences ETDs

Ryan Crow

Publication Date

1-30-2013

Abstract

This thesis focuses on the effects of volcanism, river incision, epeirogenic uplift, and faulting on the landscape evolution of the Grand Canyon region. In the first chapter the migration of increasingly asthenospheric basaltic volcanism is used to constrain lithospheric modification of the Colorado Plateau margins. Buoyancy modification of the upper mantle, driven by the upwelling, is a likely driver for recent uplift of the area. In the second chapter, correlation between oversteepened rivers and areas of high-velocity upper mantle is used to show that recent and ongoing mantle-driven uplift is modulating the surface along the western margin of the Colorado Plateau. Differential oversteepening of rivers in the Zion National Park area can't be explained by climatic or bedrock-hardness differences and are best explained by localized uplift of the area, which explains the area's high relief and dramatic slot canyons. In the third chapter, new geochronology and geochemistry are used to reconstruct the timing, sequence, and structure of Grand Canyon's lava dams. Associated gravel deposits, internal cooling structures, and a general lack of lacustrine deposits suggests that the dams were removed in multiple stages and probably did not last for more than a few hundred to thousand years. Perched gravels under lava dams show steady incision rates indicating that the blockages were ephemeral and did not significantly affect long-term bedrock incision. In the final chapter, new Grand Canyon incision rates are used to quantify the spatial and temporal variations in incision. Results show temporally steady incision at any one location and a spatial pattern of increasing incision towards the east. This spatial pattern is most consistent with differential uplift of the area. Temporally steady incision suggests a lack of transient incision most consistent with sustained uplift. These studies suggest at the landscape of the region is young and actively being modified by deep forcing. Recent mantle-driven uplift associated with the convective modification of the lithosphere has steepened rivers and driven incision of deep canyons. Repeated lava damming of the Colorado River by comparison had a much smaller effect on the geomorphology or incision history of Grand Canyon.

Degree Name

Earth and Planetary Sciences

Level of Degree

Doctoral

Department Name

Department of Earth and Planetary Sciences

First Committee Member (Chair)

Laura, Crossey

Second Committee Member

Yemane, Asmerom

Third Committee Member

William, McIntosh

Project Sponsors

Geological Society of American, University of New Mexico Office of Graduate Studies and Graduate and Professional Student Association, National Science Foundation

Language

English

Keywords

Grand Canyon, Tectonic Geomorphology, Mantle Evolution, Epeirogenic Uplift, Colorado River, Colorado Plateau, Nd Isotopes, Ar/Ar dating, U-series dating, Lava Dams, Bedrock Incision

Document Type

Dissertation

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