http://hdl.handle.net/1957/7889 Search the Channel search http://ir.library.oregonstate.edu/jspui/simple-search http://hdl.handle.net/1957/13003 Title: Stratigraphy, sedimentology, and eruptive dynamics of the 2-ka eruption of Misti Volcano, southern Peru<br/><br/>Authors: Harpel, Christopher J.<br/><br/>Abstract: The 2-ka eruption of Misti volcano produced voluminous flowage deposits and a wide-spread tephra-fall deposit. The flowage deposits form large terraces within channels draining the south side of the volcano. All the channels drain into the city of Arequipa. Arequipa's city center is ~16 km from the summit of the volcano. The large proximal population and historical unrest make volcano hazards assessment critical at Misti.The 2-ka flowage deposits are previously identified as pyroclastic-flow deposits. Abundant sedimentological and textural evidence suggests that 0.04 km³ (~80%) of these deposits are lahar deposits. Pyroclastic flows melted ~0.06 km³ of snow and ice on the volcano triggering ≤0.02-km³ lahars that inundated the southern channels and some interfluves.The downstream evolution of the lahars is represented by four facies. Small, bulking debris flows from the upper flanks of the volcano emplaced the proximal facies. Several large debris flows both bulking and debulking resulted in the terrace facies.Deposition upstream progressively thinned and diluted the flows resulting in the medial facies. Debulking and dilution continued until the flows became hyperconcentrated flows and deposited the distal facies.The 2-ka eruption was a VEI 4 that produced a 1.4-km³ tephra-fall deposit and 0.01 km³ of pyroclastic-flow deposits in ~3–5 h. Pyroclastic flows descended the southern flanks of the volcano. Column heights ≤27 km and winds dispersed the tephra fall southwest, resulting in ~20 cm of tephra in Arequipa.Pyroclastic flows and tephra fall of the same magnitude as the 2-ka eruption could occur again. Few people live in the high pyroclastic-flow hazard area but a large population live within the low hazard zone. Significant tephra fall could occur in Arequipa and would severely affect the city. There is not enough water available under modern climate conditions to generate lahars as voluminous as the 2-ka lahars. Water available under modern conditions suggests that lahars with volumes ≤1x10⁵–3x10⁶ m³ are possible. Lahars ≤1x10⁷ m³ would be possible if the Rio Chili were dammed during an eruption. Lahar hazards zones evaluated on the basis of these volumes, suggest that the largest of these lahars could enter Arequipa.<br/><br/>Description: Graduation date: 2010 http://hdl.handle.net/1957/12700 Title: Development of continental magmatic systems : insights from amphibole chemistry of the Altiplano Puna Volcanic Complex, Central Andes<br/><br/>Authors: Abot, Manggon<br/><br/>Abstract: The pressure history of a continental magmatic system can be deciphered by analyzing the composition of amphiboles in the eruptive products where the pressure of equilibration correlates with the depth of the magmatic system. This can reveal vertical evolution of the magma as amphibole composition varies significantly with temperature and pressure. The Altiplano Puna Volcanic Complex (APVC) is a long-lived and large continental magmatic system that has produced episodic ignimbrite eruptions during the last 10 m.y. The amphiboles from ignimbrites of the various stages during the 10 Ma history have been analyzed, classified and the pressure and temperature calculated using thermodynamic calculation. The APVC amphiboles are calcic amphiboles and are magnesiohornblende, tschermakite, magnesiohastingsite, and edenite based on the Leake et al. (1997) classification and based on the Deer et al. (1992) scheme. The amphiboles are also calcic, namely, hornblende, tschermakite, pargasite, and edenite. They are broadly similar to amphiboles from other calc-alkaline dacitic systems through space and time. The calculated P-T conditions range from 0.2 to 2.5 kbar and 765°C to 871°C. The P-T conditions are generally similar throughout the 10 Ma time frame of the APVC, although higher minimum and maximum pressures are recorded in the most voluminous 4 Ma pulse. The APVC magmas are representative of calc-alkaline dacitic magmas associated with subduction and therefore it is a useful model for how large calc-alkaline dacitic systems might evolve. The lack of an obvious trend in P and T with time during the 10 million years history of the APVC, suggests that evolution of dacitic magmas prior to eruption is limited to a narrow depth range in the crust, which is probably primarily controlled by the density of the magmas.<br/><br/>Description: Graduation date: 2010 http://hdl.handle.net/1957/12620 Title: Volcanism and faulting along the northern margin of Oregon’s High Lava Plains : Hampton Butte to Dry Mountain<br/><br/>Authors: Iademarco, Michael J.<br/><br/>Abstract: Oregon’s High Lava Plains Province (HLP) has strongly bimodal basalt and rhyolitic volcanism. The Province caps the northern margin of the Basin and Range Province and serves as a transitional region between westward extension of the Basin and Range Province and unextended crust to the north . The High Lava Plains overlap an area dominated by abundant minor northwest-striking faults of the Brothers Fault Zone. About 10 million years ago, silicic volcanism began at the eastern end of the HLP and spread west, younging towards the Cascade arc. Basalts erupted along the HLP are not age progressive. Most work in the High Lava Plains and Blue Mountains has left the interface between the two provinces as a nondescript region with few data capable to provide insight into processes active within this transitional region. This thesis focuses on the transition near Hampton Butte. New 40Ar-30Ar ages for Hampton Butte and adjacent Cougar Butte definitively assign both to volcanism during the emplacement of the John Day Formation and indicates a common origin. These units underlie basalts and an andesite that have ages consistent with a pulse of basaltic volcanism along the High Lava Plains around 8 Ma. An ignimbrite with composition and age (3.8 ± 0.6 Ma) consistent with outcrops at Espeland Draw, near the town of Hampton, has a probable origin at Frederick Butte and is grouped here as the Hampton Tuff. Further east, along the northern margin of the HLP, an age of 4.18 (± 0.14 Ma) was obtained for the basaltic andesite scoria cone of Grassy Butte. At Dry Mountain a summit sample produced an age of 7.91 ± 0.12 Ma and is basaltic, a contradiction with previous reports. A sample of rhyolite from Potato Hills, adjacent to Hat Butte, yielded an age of 6.52 ±.07 Ma.Basaltic melts of this study appear to be near direct partial melts of the mantle and are part of the volcanism of the High Lava Plains related to fault propagation and extension. More evolved magmas of the High Lava Plains originate from isobaric fractionation in isolated small magma chambers with little if any assimilation. The eruption of these lavas may be a result of the timing between northeast to southwest extension and Basin and Range east to west extension. The older (> 20 Ma) high silica rocks of Hampton Buttes are the result of diverse fractional crystallization paths from a common basaltic source with little or no assimilation.<br/><br/>Description: Graduation date: 2010 http://hdl.handle.net/1957/11963 Title: Geology and geochemistry of the Oregon mountain area, southwestern Oregon and northern California<br/><br/>Authors: Vail, Scott Garret<br/><br/>Abstract: The Oregon Mountain area contains an ophiolitic assemblage of rocks which can he divided into two major zones on the basis of lithology: (1) spilite and diabase, with minor chert, and (2) plagiogranite, hornblende gabbro, cumulate gabbro and cumulate ultramafic rocks. The two zones have a total estimated thickness of about 4.6 km. The lower contact of the cumulate zone is gradational into the Josephine Peridotite, an extensive body of alpine-type harzburgite. The uppermost spilites are depositionally overlain by the Galice Formation (Jurassic, Kimmeridgian). Rocks in the diabase-spilite zone haveundergone metamorphism similar to sea-floor burial metamorphism.Metamorphic grade progresses from zeolite facies through chlorite,epidote and actinolite zones of the greenschist facies to amphibolite facies. Prehnite-pumpellyite facies metamorphism has been superimposed on the lowest temperature assemblages, probablyowing to later burial by the Galice Formation. The plutonic zoneconsists of a sequence of ultramafic and mafic cumulate rocks which culminates in a residue of granophyric plagiogranite. Hornbiende gabbro, in part cumulate and in part intrusive, occurs near the top of the sequence.The Josephine Peridotite consists of olivine-rich harzburgiteand minor amounts of dunite, chromitite and pyroxenite, all withtectonite textures. It is essentially indistinguishable from otheroccurrences of alpine-type harzburgite.The Galice Formation is predominantly slaty shale. Lithicgraywacke and pebbly conglomerate are volumetrically minor components. The graywacke contains abundant quartz, volcanic fragments with minor feldspar, mafic minerals and metamorphic fragments which indicate a mixed continental and volcanic arc provenance.Rocks of the Oregon Mountain area chemically resemble otherwell known and well studied ophiolites. Major element variations in the diabase-spilite zone are interpretable in terms of sea water interacton with mid-ocean ridge tholeiite. Increases in SiO₂, Na₂O, H₂O and FeO and decreases in CaO and MgO relative to mid-ocean ridge basalts were observed in most specimens. Less consistent changes occur in K₂O, Al₂O₃, TiO₂ and MnO.Titanium and zirconium abundances suggest affinities to mid-oceanridge basalts, but there is some evidence of mobilization ofthese elements.Rare earth element distributions in rocks from the diabasespilitezone appear to have been generally unchanged during metamorphismalthough modification of Ce abundance has evidently occurredin one specimen. The distribution patterns are typically flat(La/Lu = 1 - 1.5) with low abundances (av. La = 15x chronditic abundance) indicating that basaltic rocks from the Oregon Mountain area have affinities with mid-ocean ridge basalts and arc tholeiites.Theoretical models indicate that a 15 to 20 percent melt of mantlesource rock with a REE abundances about 2 to 3 times those ofchondrites is a reasonable mechanism to produce the observed REEdistributions.The ophiolite exposed in the Oregon Mountain area apparentlyformed as oceanic crust in a marginal basin environment duringJurassic time prior to the Nevadan Orogeny. The marginal basinprobably lay between the Rogue-Galice island arc and the westerncontinental margin. Nevadan deformation telescoped the arc-marginal basin terrain and caused accretion of the Jurassic rocks onto the continental margin.<br/><br/>Description: Graduation date: 1977