Timescales of magma genesis and the dynamics of processes that produce differentiated alkalic volcanism
Abstract/Contents
- Abstract
- Volcanic provinces that erupt compositionally diverse lavas are indicative of dynamic and evolving magmatic systems at depth. Determining the processes and the timescales required to produce such a variety of magmas is a fundamental question in understanding the eruptive potential of volcanoes and the hazards associated with volcanic evolution. This dissertation explores two intraplate volcanic regions where basaltic magmas are the dominant erupted compositions, yet small volume differentiated alkalic magmas are also present. Textural, geochemical, and geochronologic methods are integrated to decipher how and when the differentiated magmas are produced. The first part of this study focuses on trachytic lavas from the intraplate volcanic field of Harrat Rahat in western Saudi Arabia. Chapter 1 relies on analysis of mineral phases present in the trachyte lavas to determine the generation processes and storage conditions of the evolved magmas. In addition, U-series disequilibrium dating of bulk mineral separates was employed to determine crystallization timescales of the trachyte magmas prior to eruption. These data are compared to previously determined 40Ar/39Ar eruption ages of the young (< 180 kya) trachyte lavas and provide necessary information for assessing the potential of future differentiated eruptions. The second part of this study investigates the differentiated alkalic lavas that were erupted during the waning volcanic period of hotspot magmatism, referred to as the postshield stage, at Kohala volcano in Hawaii. Chapter 2 presents whole rock chemistry of the postshield lavas at Kohala as well as new 40Ar/39Ar eruption ages. The new geochronologic data are in good agreement with the limited previous age constraints but show a clustering of eruptions occurring over a brief period during the stage. This high frequency of eruptions along with changes in lava chemistry over time likely requires incorporation of a different melt source during the postshield stage. Here, it is hypothesized that this period of frequent eruptions could correspond to a mass wasting event at Kohala that enhanced melting. Chapter 3 further investigates the postshield processes at Kohala through textural and chemical analysis of the lavas and reveal pervasive mixing textures throughout the volcanic suite. Major and trace element chemistry of rare apatite phenocrysts in the Kohala lavas show near-rim zoning in the crystals which is utilized to assess chemical changes that occurred in the magmatic system. Modeling of strontium diffusion in apatite is used to interpret mixing timescales that occur before eruption of the postshield lavas. These two chapters combined illustrate the necessity of new inputs of magma to the system prior to eruption of postshield lavas for Hawaiian volcanoes
Description
| Type of resource | text |
|---|---|
| Form | electronic resource; remote; computer; online resource |
| Extent | 1 online resource |
| Place | California |
| Place | [Stanford, California] |
| Publisher | [Stanford University] |
| Copyright date | 2020; ©2020 |
| Publication date | 2020; 2020 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Author | Witter, Molly Rose |
|---|---|
| Degree supervisor | Grove, Marty, 1958- |
| Thesis advisor | Grove, Marty, 1958- |
| Thesis advisor | Pamukcu, Ayla Susan |
| Thesis advisor | Suckale, Jenny |
| Thesis advisor | Vazquez, Jorge |
| Degree committee member | Pamukcu, Ayla Susan |
| Degree committee member | Suckale, Jenny |
| Degree committee member | Vazquez, Jorge |
| Associated with | Stanford University, Department of Geological and Environmental Sciences. |
Subjects
| Genre | Theses |
|---|---|
| Genre | Text |
Bibliographic information
| Statement of responsibility | Molly Rose Witter |
|---|---|
| Note | Submitted to the Department of Geological & Environmental Sciences |
| Thesis | Thesis Ph.D. Stanford University 2020 |
| Location | electronic resource |
Access conditions
- Copyright
- © 2020 by Molly Rose Witter
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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