ORCID

http://orcid.org/0000-0002-7282-1604

Date of Award

Winter 12-15-2021

Author's School

Graduate School of Arts and Sciences

Author's Department

Earth & Planetary Sciences

Degree Name

Doctor of Philosophy (PhD)

Degree Type

Dissertation

Abstract

This thesis connects mineralogical, chemical, and physical observables in quenched mafic inclusions from Shiveluch Volcano in Kamchatka and high pressure and temperature experiments to elucidate the water content of primitive magmas at Shiveluch, the timing of magmatic recharge events relative to eruption, and the petrogenetic history of andesites erupted at Shiveluch. Using the petrology of basaltic andesite mafic inclusions erupted from Shiveluch, in Chapter 2, the water content of primitive magmas at Shiveluch is found to be 8-10 wt%, which is two to three times higher than the global average determined by other methods, and the temperature of primitive magmas was found to be 1062+/-48degrees C, consistent with high magmatic water contents. The high water contents and low temperatures of these magmas are conducive to amphibole crystallization throughout the liquid line of descent. In Chapter 3, the oxidation state of iron in amphibole is developed as a magmatic oxybarometer applicable to hydrous magmas using XAFS analysis of synthetic amphibole in piston cylinder experiments. The oxybarometer is applied to natural amphibole in the mafic inclusions studied in Chapter 2, and only two samples appear to preserve the oxygen fugacity of their equilibrium magmas. The difference between the measured oxidation state of iron in natural amphibole and the expected oxidation state is equated to the timing of mafic recharge events (which led to enclave formation) relative to eruption, and we find that three distinct mafic recharge events within three months of eruption are preserved in the mafic enclaves. Finally, in Chapter 4, the products of high pressure and temperature experiments are compared to the quenched mafic inclusions studied in Chapter 2 and erupted andesites at Shiveluch in order to understand the genesis of andesite erupted at Shiveluch. Only experiments run at high water content reproduce the phase assemblages observed in mafic enclaves, meaning that andesites are at least in part formed through fractional crystallization of a superhydrous magma. The comparison of experiments and natural samples also shows that some crustal processes not represented in our experiments like magma mixing are required to produce the andesites. The findings of this thesis are relevant to magmatism at subduction zone settings, and inform our understanding of magmatic processes and volcanism at those settings worldwide.

Language

English (en)

Chair and Committee

Michael J. Krawczynski

Committee Members

David A. Fike

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