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Modeling the mantle genesis of basalts from the Lassen Volcanic Center

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There are many outstanding questions regarding the petrologic processes that give rise to andesitic and basaltic magmas in subduction zones, including the specifics that govern their geographical distribution in a

There are many outstanding questions regarding the petrologic processes that give rise to andesitic and basaltic magmas in subduction zones, including the specifics that govern their geographical distribution in a given arc segment. Here I investigate the genesis of calc-alkaline and tholeiitic basalts from the Lassen Volcanic Center in order to determine the pressure, temperature, source composition, and method of melting that lead to the production of melt in the mantle below Lassen. To this aim, a suite of primitive basalts (i.e. SiO2<52 and Mg#>65) are corrected for fractional crystallization by adding minerals back to the bulk rock composition with the goal of returning them to a primary composition in equilibrium with the mantle. Thermobarometry of the primary melt compositions is conducted to determine temperature and pressure of melting, in addition to a forward mantle modeling technique to simulate mantle melting at varying pressures to constrain source composition and method of melting (batch vs. fractional). The results from the two techniques agree on an average depth of melt extraction of 36 km and a source composition similar to that of depleted mantle melted by batch melting. Although attempted for both calc-alkaline and tholeiitic basalts, the fractional crystallization correction and thus the pressure-temperature calculations were only successful for tholeiitic basalts due to the hydrous nature of the calc-alkaline samples. This leaves an opportunity to repeat this study with parameters appropriate for hydrous basalts, allowing for the comparison of calc-alkaline and tholeiitic melting conditions.

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  • 2015-05

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Scientific and cultural interpretations of volcanoes, 1766-1901

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Scientific and Cultural Interpretations of Volcanoes, 1766-1901 analyzes nineteenth-century conceptions of volcanoes through interdisciplinary literature and science studies. The project considers how people in the nineteenth century used science, aesthetics,

Scientific and Cultural Interpretations of Volcanoes, 1766-1901 analyzes nineteenth-century conceptions of volcanoes through interdisciplinary literature and science studies. The project considers how people in the nineteenth century used science, aesthetics, and other ways of knowing to understand volcanoes and their operations. In the mid-eighteenth century, volcanoes were seen as singular, unique features of the planet that lacked temporal and terrestrial reach. By the end of the nineteenth century, volcanoes were seen as networked, environmental phenomena that stretched through geological time and geographic space. Scientific and Cultural Interpretations of Volcanoes, 1766-1901 offers a new historical understanding of volcanoes and their environmental connections, using literature and science to show how perceptions of volcanic time and space changed over 135 years.

The first chapter, using texts by Sir William Hamilton, Hester Piozzi, and Priscilla Wakefield, argues that in the late eighteenth century important aspects of volcanoes, like their impact upon human life and their existence through time, were beginning to be defined in texts ranging from the scientific to the educational. The second chapter focuses on works by Sir Edward Bulwer-Lytton and Charles Lyell to demonstrate the ways that volcanoes were stripped of metaphysical or symbolic meaning as the nineteenth century progressed. The third chapter contrasts the 1883 eruption of Krakatoa with Constance Gordon-Cumming’s travels to Kīlauea. The chapter shows how even towards the end of the century, trying to connect human minds with the process of volcanic phenomenon was a substantial challenge, but that volcanoes like Kīlauea allowed for new conceptions of volcanic action. The last chapter, through a post-apocalyptic novel by M. P. Shiel, shows how volcanoes were finally beginning to be categorized as a primary agent within the environment, shaping all life including humanity. Ultimately, I argue that the change in thinking about volcanoes parallels today’s shift in thinking about global climate change. My work provides insight into how we imagine ecological catastrophes like volcanic eruptions or climate change in the past and present and what that means for their impact on people.

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Date Created
  • 2016