Polyphase deformation and metamorphism : a geochronologic perspective
Abstract/Contents
- Abstract
- The use of combined geochronology, structural geology, petrology and geochemistry on exhumed deep crustal rocks can be used to unravel protracted histories of tectonic events that create and modify continental crust. The highly extended Basin and Range province of western U.S. contains countless exposures of mid-lower crustal rocks that offer an excellent opportunity to study deep crustal processes. Two examples of this approach are described here: The Albion-Raft River-Grouse Creek (ARG) metamorphic core complex of southern Idaho and northern Utah, and the Ivanpah Mountains of the Mojave crustal province of southeastern California. The lower plate of the ARG metamorphic core complex consists of deformed and metamorphosed 2.56 Ga crystalline basement and highly attenuated, Neoproterozoic supracrustal rocks that were intruded by 32-25 Ma syn-extensional plutons of the greater Cassia batholith. Crystallization temperatures of these plutons based on Ti concentrations in zircon range from 603-812 °C, and are mostly below 700 °C, suggesting hydrous melt conditions. Very low negative whole rock [epsilon]Nd values of the Oligocene granites ([epsilon]Nd = -25 to -36) and abundant, Late Archean inherited zircons contained within them indicate that the Cassia batholith formed from melting of late Archean crust that underlies the region. Deformation occurred in the country rocks to these plutons during sillimanite grade metamorphism, ductile attenuation and normal-sense shear along the Middle Mountain shear zone. Detailed study of an attenuated section of the country rocks to the Oligocene plutons revealed protracted (32-26 Ma) monazite growth and indicates an older period of metamorphism (~ 140 Ma) as preserved in monazite cores and metamorphic zircon rims on detrital grains. In the Ivanpah Mountains, exposures of Paleoproterozoic banded gneisses have been exhumed from deep crustal levels by Basin and Range extension. The granulite facies rocks preserved here contain a record of multiple tectonic events related to crustal formation of the North American continent. Orthogneisses and paragneisses are strongly deformed, partially melted and isoclinally folded with a penetrative, N-S-trending folding and migmatitic layering that dips steeply to the west. Samples of metaigneous and metasedimentary rocks were analyzed for U-Pb geochronology of zircon and monazite using the SHRIMP-RG. I use trace elements in zircon, in situ monazite dating, and thermobarometry to show that copious garnet growth and the formation of the dominant, N/S striking fabric developed under metamorphic conditions of 4-6 kb and ~750 °C during the final metamorphic event at ~1.67-1.66 Ga.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2010 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Strickland-Roll, Ariel |
|---|---|
| Associated with | Stanford University, Department of Geological and Environmental Sciences. |
| Primary advisor | Miller, Elizabeth |
| Thesis advisor | Miller, Elizabeth |
| Thesis advisor | Graham, S. A. (Stephan Alan), 1950- |
| Thesis advisor | Wooden, Joseph L |
| Advisor | Graham, S. A. (Stephan Alan), 1950- |
| Advisor | Wooden, Joseph L |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Ariel Strickland-Roll. |
|---|---|
| Note | Submitted to the Department of Geological and Environmental Sciences. |
| Thesis | Ph. D. Stanford University 2010 |
| Location | electronic resource |
Access conditions
- Copyright
- © 2010 by Ariel Strickland-Roll
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