Geochemical homogeneity of a long-lived, large silicic system; evidence from the Cerro Galan caldera, NW Argentina

Christopher Folkes, Shanaka De Silva, Heather Wright, Raymond Cas

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    Abstract

    By applying a number of analytical techniques across a spectrum of spatial scales (centimeter to micrometer) in juvenile components, we show that the Cerro Galan volcanic system has repeatedly erupted magmas with nearly identical geochemistries over > 3.5 Myr. The Cerro Galan system produced nine ignimbrites (similar to 5.6 to 2 Ma) with a cumulative volume of > 1,200 km(3) (DRE; dense rock equivalent) of calc-alkaline, high-K rhyodacitic magmas (68-71 wt. SiO(2)). The mineralogy is broadly constant throughout the eruptive sequence, comprising plagioclase, quartz, biotite, Fe-Ti oxides, apatite, and titanite. Early ignimbrite magmas also contained amphibole, while the final eruption, the most voluminous Cerro Galan ignimbrite (CGI; 2.08 +/- 0.02 Ma) erupted a magma containing rare amphibole, but significant sanidine. Each ignimbrite contains two main juvenile clast types; dominant white pumice and ubiquitous but subordinate grey pumice. Fe-Ti oxide and amphibole-plagioclase thermometry coupled with amphibole barometry suggest that the grey pumice originated from potentially hotter and deeper magmas (800-840A degrees C, 3-5 kbar) than the more voluminous white pumice (770-810A degrees C, 1.5-2.5 kbar).
    Original languageEnglish
    Pages (from-to)1455 - 1486
    Number of pages32
    JournalBulletin of Volcanology
    Volume73
    Issue number10
    DOIs
    Publication statusPublished - 2011

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