A Study on Magmatic Diversity: Determining the Evolution and Petrogenesis of Eocene Magmatism at Swales Mountain, NV
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Authors
Florez, Shasta Rosa-Longo
Issue Date
2023
Type
Thesis
Language
Keywords
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Abstract
Modern volcanic systems are commonly not static but change through time as magmas are added from below and tapped during eruption. From the Eocene to Miocene, the Great Basin underwent a magmatic episode tied to slab rollback of the Farallon plate. Swales Mountain, Nevada, hosts a complex shallow to mid-crustal Eocene magmatic system (39.5-35.5 Ma) that, due to Basin and Range extension, are exhumed and exposed today at the Earth surface. This study provides an updated 1:5,000 geologic map, new U-Pb zircon ages, amphibole barometry, Sr-Nd-Pb isotopic data and whole rock major and trace element geochemistry to explore the temporal, spatial, and petrologic evolution of the Swales Mountain magmatic system over its ~4 Ma activity. The six calc-alkaline, high-K, intrusive and subvolcanic units range from 56 to 76 wt% SiO2. Three texturally and compositionally distinct plutons ranging 0.5-2 km in width are exposed in different parts of the plumbing system. In between, various dikes, sills, and breccias interact with Paleozoic sedimentary units. A variety of mixing textures with mafic material have been observed in the plutonic units, indicating contemporaneous existence of distinct magmas in the Swales Mountain system. Swales Mountain is ~17 km northeast of the Carlin Trend allowing the Swales intrusions to be a potential heat and fluid source leading to Carlin-type mineralization.Results indicate that Swales Mountain had at least two episodes of magmatism: the first being a smaller event lasting ~100 ka generating the Eastern Swales quartz monzodiorite at a relatively shallow depth, and the second event lasting ~ 3.1 Myr producing the Central Swales quartz monzonite, Southern Swales monzogranite, dacite porphyry, and rhyolite. Basaltic andesite dikes intrude the dacite porphyry and rhyolite. I speculate that the Swales magmatic system came from a lithospheric mantle source that experienced upper crustal assimilation and homogenization. Small compositionally diverse systems, such as Swales Mountain, may potentially be used to explore how initial crustal magmatism integrates mantle material over time.