Earth and Planetary Sciences ETDs

Publication Date

9-9-2010

Abstract

U-Pb dating of 1035 detrital zircons from twelve spatially-distributed samples of the Paleoproterozoic Vishnu Schist reveals a bimodal 207Pb/ 206Pb age probability diagram with peaks at 1.8 Ga and 2.5 Ga. Surprisingly, only 13% of detrital zircon ages overlap with the published depositional age range of 1750–1741 Ma. The similarity of the age distributions in all samples constrains possible suturing of crustal blocks to pre-Vishnu Schist deposition rather than during the peak 1710-1680 Ma deformation. Of all grains analyzed, 15% overlap at 2σ with the 1.84 ± 1 Ga Elves Chasm orthogneiss of western Grand Canyon. This supports field evidence that Vishnu Schist was deposited on 1.84 Ga arc basement rather than in a juvenile 1.75 Ga arc setting. Archean grains of 3.8–2.5 Ga comprise 30% of all grains. A comparison of the > 2.2 Ga ages from the Vishnu Schist (495 grains) with compilations of zircon ages from other cratons does not support provenances in the Wyoming, South China, or Siberian cratons; instead sources may be located in Gawler craton of Australia, North China craton, or Antarctica. If the detrital zircons were far-traveled, this is a new constraint for viable reconstructions of the Nuna supercontinent. However, given the high percentage of pre-1.8 Ga zircons, unexposed proximal basement sources are more likely, resulting in a model by which Vishnu sediments were derived from Mojave crust that consists of Archean and 1.9-1.8 Ga crust, now in the subsurface, that was unroofed during Vishnu deposition.

Degree Name

Earth and Planetary Sciences

Level of Degree

Masters

Department Name

Department of Earth and Planetary Sciences

First Advisor

Karlstrom, Karl E.

First Committee Member (Chair)

Crossey, Laura

Second Committee Member

Asmerom, Yemane

Third Committee Member

Whitmeyer, Steven

Project Sponsors

National Science Foundation, Geology Alumni Association of the University of New Mexico, Geological Society of America

Language

English

Keywords

Precambrian geology, detrital zircons

Document Type

Thesis

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