Undergraduate Honors Theses

Thesis Defended

Spring 2015

Document Type

Thesis

Type of Thesis

Departmental Honors

Department

Geological Sciences

First Advisor

Charles Stern

Second Advisor

Lang Farmer

Third Advisor

Michael Barnett

Abstract

The production of small volume silicic rocks in areas of oceanic crust is understood with less certainty than the production of silicic rocks in a continental setting. While the anatexis of silicic continental crust produces rhyolites within a continent, it is unlikely to occur in Iceland, an island composed of basaltic oceanic crust. After analyzing rhyolitic samples I collected from multiple locations throughout Iceland and samples from the Valles Caldera, a large volume rhyolitic body in New Mexico, chemical and petrologic differences between the samples confirmed that different processes form continental and island rhyolites. Trace element geochemistry of Icelandic rhyolite samples shows that closed-system crystal fractionalization is likely the primary driver behind the production of silicic magmas in oceanic island settings, although it has previously been argued that the anatexis of altered basaltic crust also plays a role. Variations in degrees of fractionation of parental melt and parental melt chemistry are responsible for chemical variations within Icelandic samples. Contrastingly, liquid-state differentiation is the source of a lone geochemical outlier amongst Valles rhyolites. For this question of island rhyolite genesis to be answered with greater certainty, a more in depth and complex study would need to be conducted.

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