Continental and Island Rhyolites

• Main Author: Guido, Michael
• Format: Text
• Language: unknown
• Published: CU Scholar 2015
• Subjects: Iceland; Valles Caldera; rhyolites; anatexis; fractionation; Geochemistry; Geology; Volcanology; Lone; Valles
• Online Access: https://scholar.colorado.edu/honr_theses/864; https://scholar.colorado.edu/cgi/viewcontent.cgi?article=2068&context=honr_theses

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.