Geology Commons^™

Shared Roots: A Geochemical Investigation Of Basaltic Andesites To Understand Magmatic Cogenesis At The Middle Sister And South Sister Volcanoes, Central Oregon, Sean Francis Halstead

WWU Honors College Senior Projects

The Middle Sister and South Sister volcanoes, near Bend, Oregon, are overlapping, active Cascade Arc stratovolcanoes which share a complex, contemporaneous eruptive history. This history is characterized by an extreme compositional diversity of lavas erupted in alternating phases of high activity from one neighboring volcano to the other, with both vents producing material ranging from basaltic andesite to rhyolite. This system is understood to be predominantly fed by basaltic andesites fractionated from partial mantle melts within the lower crust, but magma compositions are additionally impacted by mixing, assimilation, and crustal contamination while in transit to the surface. Thus, the subterranean …

Populations Of Major Phases In Glacier Peak Lavas, Charlotte Wall

Geology Graduate and Undergraduate Student Scholarship

Volcanoes can be studied through minerals that are present in their eruption products. These minerals can be studied through optical microscopy and geochemistry to better understand their origins and provide insight into which processes took place prior to eruption (i.e., fractionation of crystals, assimilation of the surrounding crust, magma mixing). In this study I examine mineral populations in dacite (lava of intermediate composition) from Dahkobed/Glacier Peak volcano in the north Cascade Arc. The samples consist of a felsic (high SiO2) host component and a mafic (low SiO2) inclusion component. To establish base mineral populations, minerals from both the host and …

Using Clinopyroxene Mineral Chemistry To Decipher Magma Composition Changes Over The 13 Million Year History Of The Izu-Bonin Volcanic Arc, Erin Benson

Geology Graduate and Undergraduate Student Scholarship

International Ocean Discovery Program Expedition 350 recovered 2000 meters of volcanic rock core in spring, 2014 at the Izu-Bonin-Mariana Rear Arc. The core has been divided into seven lithostratigraphic units, from age 0 at the top to at least 13 million years at the bottom. The major and trace element geochemistry of representative mineral grains in volcaniclastic rocks throughout the core from top to bottom were analyzed and used as a proxy for interpreting magma compositional changes through time. The clinopyroxene from all units and the glass from Unit I were analyzed for major elements (by SEM and electron microprobe) …

The Stratigraphy And Geochemistry Of The Crescent Formation Basalts And The Bedrock Geology Of Associated Igneous Rocks Near Bremerton, Washington, Kenneth P. Clark

WWU Graduate School Collection

A stratigraphic section developed for the Bremerton rocks in the Kitsap Peninsula suggests formation by rifting in a marine environment. Basal gabbro, dated by 40Ar/39Ar at 49.8 Ma plus or minus 0.8 Ma, and associated mafic to felsic plutonics, appear to be the source of a mafic dike complex that composes 100% of the stratigraphic level above the plutonics. These dikes are the apparent feeders to overlying submarine and subaerial volcanics. The previously unrecognized submarine sequence consists of interbedded basaltic breccia, tuffs, basalt flows, and basaltic sandstone, siltstone, and conglomerate. Approximately 1 km of columnar basalt flows cap the sequence. …

Petrology And Major Element Geochemistry Of Albite Granite Near Sparta, Oregon, Robert Brayton Almy Iii

WWU Graduate School Collection

Albite granite near Sparta, Oregon occurs in an igneous complex containing serpentinite, gabbro, diorite, tonalite and granite with overlying keratophyric and spilitic volcanic rocks. This igneous suite is overlain by Triassic limestones of reef origin. In all the igneous rocks primary hypidiomorphic and porphyritic textures predominate but a metamorphic overprint of the prehnite-pumpellyite facies is widespread. Whole rock chemical analyses show that albite granite has relatively high Si0₂ (69-81%) and Na₂0 (4-7%) and low K₂O (0.1-1%). Rare plagioclase potassium-feldspar granite contains up to 3.6% K₂O.

Although local isochemical alteration is demonstrable and local …