SAMANTHA DUNN
Current Research
In the summer of 2022, from July 16th to August 12th, I spent four weeks mapping approximately 17 sq. kilometers of the Jackass Lakes Pluton (JLP) at a 1:10,000 scale. The JLP is located in the Sierra Nevada National Forest and has exposed volcanics from the Minarets and Merced Peak calderas. My thesis is focused on the volcanic-plutonic connection between the JLP and surrounding volcanics to see whether the units are complementary or equivalent systems. Through my study, I will complete a thorough petrological study of the JLP, along with U-Pb geochronology of the JLP, associated volcanics, and porphyry. Whole rock (XRF), EMPA and LA-ICP-MS analysis will also be done.
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I am currently working on digitizing my field map of the JLP volcanic-porphyry-plutonic complex. I will also be incorporating the completed digitized map of the undergraduate primary mapper, along with previously published maps of the JLP, such as Pignotta et al. (2010). The final product will be delivered to the USGS in May 2023 to be added to their national digital geological map database and to aid in an effort to digitally geologically map the entire United States. The finished digital map will also be shared with the California Geological Survey, who are aiming to map and completely digitize the geologic map of California.
Tuffy on top of Post Peak Pass after a long and arduous hike up. The top of Post Peak is fine-grained meta-dacite, with inclusions of lithics.
The presence of past human activity was found just south of Slab Lakes, in the JLP granodiorite.
Mafic enclave swarms within the main phase of the JLP. Enclaves are fine-grained and appear to be quartz diorite. The swarms are common throughout the main phase of the JLP granodiorite.
Past Research
Petrography and Geochemistry of the Holocene Inconstance Lava Flow, Hotlum Cone, Mt. Shasta, California
Magma reservoirs that feed volcanic eruptions are thought to spend most of their existence at temperatures near their solidus in as viscous and uneruptible “crystal-rich mush” (e.g., Cooper and Kent, 2014). Only during the weeks and months prior to and after volcanic eruptions are magmas thought to exist as eruptible fluids. Understanding the processes that transform these crystal mushes into eruptible fluids is a critical aspect of mitigating volcanic hazards. This study examined samples from the Inconstance Creek lava flow, on the eastern side of Mount Shasta. Sampling was completed strategically with three samples taken along the levees of the flow and three from the center of the flow to analyze if there was any compositional zoning occurring in the magma chamber prior to eruption. To test this hypothesis, petrological and geochemical studies were performed of the Inconstance Creek lava flow to better understand if there was compositional zoning in the magma and if there is any evidence to suggest magma mixing as a trigger prior to eruption.
Orange outline of the Inconstance Creek lava flow from the Hotlum Cone. Last eruption was 8.5ka ago. Several effusive lave flows erupted from Hotlum Cone. Compositions of the lava range between of andesite and dacite.
Pink markers, mark the sample locations.
The yellow lines trace over coulee structures; more siliceous lava. The red lines trace over the top of the levees