Dissertation
Low-δ18O rhyolites of southwestern Idaho and vicinity
Doctor of Philosophy (PhD), Washington State University
01/2010
Handle:
https://hdl.handle.net/2376/2798
Abstract
This dissertation is divided into three chapters, each to be submitted to peer-reviewed journals, addressing the volcanology, petrology, and petrogenesis of rhyolitic volcanics in southwestern Idaho.
Chapter 1: Conflicting explanations have been advanced for the petrogenesis of basalts and low-δ18O rhyolites of the central Snake River Plain. We show that, when the Yellowstone hotspot track including the Columbia River and Steens basalts is treated as a single province derived ultimately from a common mantle source, the isotope geochemistry of these lavas and tuffs can be explained to a first order by simple binary mixing of asthenosphere-derived basalt and granitic crust of the Idaho batholith. This model is consistent with, but does not require, a stationary mantle plume as the origin of the province.
Chapter 2: Two models for the origin of low-δ18O rhyolites are currently under debate. The first, "Magmatic Autophagy" involves a single caldera system (or multiple, near contemporaneous, overlapping systems) producing hydrothermal alteration of the earliest erupted products, which are subsequently melted to form low-δ18O rhyolites. The second model appeals to a pre-existing crustal magma source, which was hydrothermally altered in a significantly prior thermal event. We critically evaluate the plausibility of each and provide thermal, temporal, and volume constraints which must be included in any model for the petrogenesis of low-δ18O rhyolites of the central Snake River Plain.
Chapter 3: Rhyolites of the western Snake River Plain erupted near contemporaneously with a number of the low-δ18O rhyolites of the central Snake River Plain, and aside from their oxygen isotope ratios, are similar in chemistry and morphology. Here, we describe the volcanology, petrology, and physical properties of these "normal" δ18O rhyolites and propose a model for their petrogenesis which invloves the melting of the middle crust straddling the boundary between the ancient craton to the east, and the younger accreted terrains to the west.
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Details
- Title
- Low-δ18O rhyolites of southwestern Idaho and vicinity
- Creators
- Scott Boroughs
- Contributors
- John A Wolff (Advisor)Bill Bonnichsen (Committee Member)Peter Larson (Committee Member)Michael McCurry (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Environment, School of the (CAHNRS)
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Number of pages
- 134
- Identifiers
- 99900581756401842
- Language
- English
- Resource Type
- Dissertation