Date of Award:

12-2018

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Geosciences

Department name when degree awarded

Geology

Committee Chair(s)

Carol M. Dehler

Committee

Carol M. Dehler

Committee

Joel L. Pederson

Committee

John W. Shervais

Abstract

Three related sedimentary successions located in Arizona, Utah, and California were deposited in basins on proto-North America during the early rifting of Rodinia (~780 Mya). Previous detrital zircon U-Pb maximum ages for the units are inexact, making it difficult to piece together what happened at this point in Earth history.

We report better maximum age constraints on these units obtained by subjecting detrital zircons to high-precision CA-ID-TIMS analysis, which provide more exact 206Pb/238U ages. These new data significantly improve the precision for the base of the ChUMP units, with an average age of 775.63 ± 0.27 Ma acquired for the bottom of the Chuar Group, where earlier work put the age at 782 Ma. An average age of 775.44 ± 0.73 Ma for the bottom of the Pahrump Group is also younger than the previously reported 787 ± 11 Ma. Zircons of the Uinta Mountain Group provided ages of about 766.88 ± 2.31 Ma, which is on par with an earlier age of 766.4 ± 4.8 Ma. These high precision ages for the young detrital zircons in the ChUMP units improve links between the units and provide better context for geochemical, isotopic, and biological events that occurred during the initial rifting of Rodinia.

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