Geology Commons^™

Compositional And Physical Gradients In The Magmas Of The Devine Canyon Tuff, Eastern Oregon: Constraints For Evolution Models Of Voluminous High-Silica Rhyolites, Shelby Lee Isom

Dissertations and Theses

Large-volume silicic ignimbrites erupt from reservoirs that vary in composition, temperature, volatile content and crystallinity. The 9.7 Ma Devine Canyon Tuff (DCT) of eastern Oregon is a large-volume (>250 km³), compositionally zoned and variably welded ignimbrite. The ignimbrite exhibits heterogeneous trace element compositions, variable volatile content and crystallinity. These observations were utilized in the investigation into the generation, accumulation and evolution of the magmas composing the DCT. Building off previous research, pumices were selected from the range of trace element compositions and analyzed with respect to crystallinity, mineral abundances and assemblages. The DCT displays a gradational trace …

Constraining The Holocene Extent Of The Northwest Meers Fault, Oklahoma Using High-Resolution Topography And Paleoseismic Trenching, Kristofer Tyler Hornsby

Dissertations and Theses

The Meers Fault (Oklahoma) is one of few seismogenic structures with Holocene surface expression in the stable continental region of North America. Only the ~37 km-long southeastern section of the ~55 km long Meers Fault is interpreted to be Holocene-active. The ~17 km-long northwestern section is considered to be Quaternary-active (pre-Holocene); however, its low-relief geomorphic expression and anthropogenic alteration have presented difficulties in evaluating the fault length and style of Holocene deformation. We reevaluate surface expression and earthquake timing of the northwestern portion of the Meers Fault to improve fault characterization, earthquake rupture models, and seismic hazard evaluations based on …

Melting In The Mantle Wedge: Quantifying The Effects Of Crustal Morphology And Viscous Decoupling On Melt Production With Application To The Cascadia Subduction Zone, Jiaming Yang

Dissertations and Theses

Arc magmatism is sustained by the complex interactions between the subducting slab, the overriding plate, and the mantle wedge. Partial melting of mantle peridotite is achieved by fluid-induced flux melting and decompression melting due to upward flow. The distribution of melting is sensitive to temperature, the pattern of flow, and the pressure in the mantle wedge. The arc front is the surface manifestation of partial melting in the mantle wedge and is characterized by a narrow chain of active volcanoes that migrate in time. The conventional interpretation is that changes in slab dip angle lead to changes in the arc …

Field Mapping Investigation And Geochemical Analysis Of Volcanic Units Within The Dinner Creek Tuff Eruptive Center, Malheur County, Eastern Oregon, Matthew Cruz

Dissertations and Theses

The Dinner Creek Tuff is a mid-Miocene rhyolitic to dacitic ignimbrite, consisting of four cooling units with ⁴⁰Ar/³⁹Ar ages 16--15 Ma. Previous geologists have suspected that the source of the tuff is located in northwestern Malheur County, eastern Oregon. This broad area is called the Dinner Creek Tuff Eruptive Center.

This thesis summarizes field work, XRF/ICP-MS geochemistry, thin section petrography, and SEM feldspar analysis from the summers of 2015 and 2016. The main purpose of this study is to identify sources for the Dinner Creek Tuff units within the Dinner Creek Tuff Eruptive Center. The secondary purpose …

Soputan Volcano, Indonesia: Petrological Systematics Of Volatiles And Magmas And Their Bearing On Explosive Eruptions Of A Basalt Volcano, Syegi Lenarahmi Kunrat

Dissertations and Theses

Soputan volcano is one of the few basaltic volcanoes among 127 active volcanoes in Indonesia. It is part of the Sempu-Soputan volcanic complex located south of Tondano Caldera, North Sulawesi and commonly produces both explosive eruptions with VEI 2-3 and effusive lava dome and flow eruptions. Over the last two decades, Soputan had thirteen eruptions, the most recent in 2016. Most eruptions started explosively, followed by dome growth and in some cases pyroclastic flows. Our study focuses on understanding the magmatic system of Soputan and what processes are responsible for its highly explosive eruptions, which are typically uncommon for a …

The Littlefield Rhyolite, Eastern Oregon: Distinct Flow Units And Their Constraints On Age And Storage Sites Of Grande Ronde Basalt Magmas, Brian Mcculloch Webb

Dissertations and Theses

The Littlefield Rhyolite consists of widespread, high-temperature, hotspot-related rhyolitic lavas that erupted in eastern Oregon contemporaneous to late-stage Grande Ronde Basalt lavas. The estimated total volume of erupted rhyolites is ~100 km³ covering ~850 km².

The focus of this study has been to investigate the stratigraphy and petrology of the Littlefield Rhyolite and whether field and geochemical relationships exist to help constrain the timing and storage sites of Grande Ronde Basalt magmas. Although often indistinguishable in the field, our data reveal that the Littlefield Rhyolite consists of two geochemically distinct rhyolite flow packages that are designated here …

Mineral Evidence For Generating Compositionally Zoned Rhyolites Of The Devine Canyon Tuff, High Lava Plains, Oregon, Erik Paul Shafer

Dissertations and Theses

Large-volume silicic eruptions are often evacuated from magma reservoirs which display gradients in composition, temperature, crystallinity, and volatile content. The 9.7 Ma Devine Canyon Tuff (DCT) of eastern Oregon represents such an eruption, with >300 km³ of compositionally zoned pyroclastic material deposited as a variably-welded ignimbrite. The ignimbrite displays homogenous bulk tuff major element compositions with a wide range of trace element compositions, allowing for the investigation of how these magmas were generated, stored, and modified in the magma reservoir by studying pumices which represent the primary magmas composing the DCT. Five pumices ranging from dacite to rhyolite bulk compositions …

Rhyolite Petrogenesis At Tower Mountain Caldera, Or, Elizabeth Ann Brown

Dissertations and Theses

Tower Mountain Caldera is the main feature of an Oligocene volcanic field located in the Umatilla National Forest, eastern Oregon. It is perfectly suited to investigate models of rhyolite petrogenesis as all of the important rock components for evaluating generation models are present in a single location and thus are presumably related; basalts, intermediate igneous rocks (which consist of older plutons and younger volcanic rocks, which are ~coeval with rhyolites), metamorphic basement rocks of significant grade, and rhyolites of varying composition. The formation of the caldera produced the Dale Tuff, which comprises the intra-caldera and outflow facies. ⁴⁰Ar/^{39 …}

Mechanisms Of Shear Zone Localization And Raman Thermobarometry In Spinel Peridotites From The Alpine Fault, New Zealand, Emily J. Lubicich

Dissertations and Theses

A suite of xenoliths from two localities on South Island, New Zealand, exhibit rare microstructures and provide information on deformation during the early stages of development of the Alpine Fault. The first set of samples has evidence of dislocation creep with subgrains, recrystallized grains, undulose extinction and a lattice preferred orientation. These samples also show evidence of post deformation static grain growth with polygonal grains, 120° triple junctions, and euhedral grains within larger grains of the same phase. Samples from the second locality also show evidence of dislocation creep but with minimal static grain growth. This set also has a …