--> Investigating the Volcanic-Plutonic Connections Using Geochemistry in the Minarets Caldera, Eastern-Central Sierra Nevada Mountain Range

AAPG Pacific Section and Rocky Mountain Section Joint Meeting

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Investigating the Volcanic-Plutonic Connections Using Geochemistry in the Minarets Caldera, Eastern-Central Sierra Nevada Mountain Range

Abstract

Studying the characteristics of a magmatic arc that is vertically extensive is challenging as typically only the volcanic parts or only the deeper, plutonic parts are exposed. The Minarets Caldera in the eastern-central Sierra Nevada mountain range, however, exposes both parts of the magmatic system. Understanding how volcanic materials and deeper magma chambers (now preserved as a pluton) are geochemically connected may help us better understand characteristics of volcanic eruptions and ultimately help with predicting volcanic eruptions. The rock record in the Minarets Caldera shows a well preserved intracaldera ignimbrite, an intercalated caldera-collapse breccia, and a granitic to granodioritic intrusion known as the Shellenbarger pluton that intruded into the center of the volcanic complex. The volcanic and plutonic rocks have been determined to be contemporaneous at ca. 100 Ma (Tomek et al., 2015) and thus connected to the same magma system. The Shellenbarger Lake pluton is thought to represent the source of the volcanic deposits (Fiske and Tobisch, 1994). The volcanic samples obtained, both around and from the Minarets caldera, and from the Shellenbarger Lake pluton can provide information on the evolution of the magma processes that occurred in the magma chamber and led to the Minarets caldera forming eruption. Studying the major and minor trace elements through XRF analysis in this caldera will give us some insight into the Minarets caldera magmatic system and how volcanoes work in general. Geochemical analyses will allow me to test how the volcanic and plutonic parts are connected: Do they represent the exact same compositions or are they complementary to one another? The latter will imply that the erupted materials may have been fractionated from the magma reservoir and the pluton represents the restitic magma. This will be tested with geochemical modeling.