Download or read book Early High Cascade Silicic Volcanism written by Daniel W. Eungard and published by . This book was released on 2012 with total page 273 pages. Available in PDF, EPUB and Kindle. Book excerpt: Silicic volcanism in the central Oregon Cascade range has decreased in both the size and frequency of eruptions from its initiation at ~40 Ma to present. The reasons for this reduction in silicic volcanism are poorly constrained. Studies of the petrogenesis of these magmas have the potential for addressing this question by providing insight into the processes responsible for producing and erupting silicic magmas. This study focuses on two extensive and well-preserved ash-flow tuffs from within the ~4-8 Ma Deschutes Formation of central Oregon, which formed after the transition from Western Cascade volcanism to the modern High Cascade. Documentation of outcrop extent, outcrop thickness, clast properties, and samples provide the means to estimate a source location, minimum erupted volumes, and to constrain eruptive processes. Major and trace element chemistry of glass and minerals constrain the petrogenesis and chemical evolution of the system. The tuffs selected for this study, the Lower Bridge and McKenzie Canyon, are the first known silicic units originating from the Cascade Arc following the reorganization from Western Cascade to High Cascade Volcanism at ~8 Ma. These eruptions were significant in producing a minimum of ~5 km3 DRE each within a relatively short timeframe. These tuffs are sourced from some vent or edifices related to the Three Sisters Volcanic Complex, and capture an early phase of the volcanic history of that region. The chemical composition of the tuffs indicates that the Lower Bridge erupted predominately rhyolitic magma with dacitic magma occurring only in small quantities in the latest stage of the eruption while McKenzie Canyon Tuff erupted first as a rhyolite and transitioned to a basaltic andesite with co-mingling and incomplete mixing of the two magma types. Major and trace element concentrations in minerals and glass indicate that the basaltic andesite and rhyolite of the McKenzie Canyon Tuff were well convected and stored in separate chambers. Geothermometry of the magmas indicate that the rhyolites are considerably warmer (~850°) than typical arc rhyolites. Trace element compositions indicate that both the Lower Bridge and McKenzie Canyon Tuff experienced mixing between a mantle derived basaltic melt and a rhyolitic partial melt derived from gabbroic crust. Rhyolites of the Lower Bridge Tuff incorporate 30-50% partial melt following 0->60% fractionation of mantle derived melts. The McKenzie Canyon Tuff incorporates 50-100% of a partial melt of a mafic crust with up to 15% post mixing fractionation. The results of this study suggest that production of voluminous silicic magmas within the Cascade Arc crust requires both fractionation of incoming melts from the mantle together with mixing with partial melts of the crust. This provides a potential explanation for the decrease in silicic melt production rates from the Western Cascades to the High Cascades related to declining subduction rate. As convergence along the Cascade margin became more oblique during the Neogene, the consequent slowing rate of mantle melt production will result in a net cooling of the crust, inhibiting the production of rhyolitic partial melts. Without these partial melts to provide the rhyolitic end member to the system, the system will evolve to the mafic melt and fractionation dominated regime that has existed along Cascadia throughout the Quaternary.

Download or read book Petrogenesis of Compositionally Distinct Silicic Volcanoes in the Three Sisters Region of the Oregon Cascade Range written by Brittain E. Hill and published by . This book was released on 1991 with total page 470 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Three Sisters region of the Oregon High Cascades has developed three compositionally and petrogenetically distinct silicic (i.e., SiO2 [greater than or equal to] 58%) magma systems within the last 600 k.y. These silicic systems evolved from the same High Cascade mafic magma system and developed in the same 20x30 km area of the arc, but did not interact. The Broken Top system (BT) evolved to 71% SiO2 through a combination of plag + px + Fe-Ti oxides ± ap (PPFA) fractionation and 20%-35% mixing of rhyolitic (74% SiO2) crustal melts. In contrast, part of the Three Sisters system (3S) evolved to 66% SiO2 through PPFA fractionation alone, while other parts evolved to 66% SiO2 through PPFA fractionation coupled with [greater than or equal to} 40% mixing of rhyolitic ([greater than or equal to]72% SiO2) crustal melts. The 3S system was intermittently active from [less than or equal to] 340 ka to 2 ka. The petrogenesis of intermediate composition rocks at Middle Sister (340 ka, 100 ka) was controlled by PPFA fractionation to [less than or equal to] 66% SiO2. Rhyolite (72%-76% SiO2) was first erupted in the 3S system at [approximately] 100 ka, at the start of South Sister (SS) volcanism. Major and trace element abundances preclude derivation of 3S rhyolite through crystal fractionation, but are consistent with 20-30% dehydration melting of mafic amphibolite. The petrogenesis of intermediate composition rocks at SS was controlled by PPFA fractionation coupled with 30-40% rhyolitic magma mixing. However, the rhyolitic magma mixed into an essentially mafic system, which limited intermediate differentiation at SS to [less than or equal to] 66% SiO2. The BT system was active from [approximately] 600 ka to at least 200 ka. Major and trace element abundances preclude derivation of BT rhyolite (74% SiO2) through crystal fractionation, but are consistent with [approximately] 30% dehydration melting of older tonalitic intrusions. BT petrogenesis was controlled by PPFA fractionation accompanied by 10-20% mixing of rhyolitic magmas to [approximately] 63% SiO2, with [approximately] 30% rhyolite mixing from 63% to 71% SiO2. In contrast to the 3S system, differentiation proceeded beyond 66% SiO2 because rhyolitic magma was mixed into a more evolved ([approximately] 60%-65% SiO2) system. The observed temporal and spatial variations in petrogenesis were not controlled by regional changes in tectonic setting, crustal thickness or crustal composition. However, small-scale changes in the magnitude of crustal extension occurred in this area, and are thought to have controlled petrogenesis by localizing mid-crustal mafic magmatism and thus crustal heat flow.

Download or read book Open file Report written by and published by . This book was released on 1978 with total page 728 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Geological Survey Professional Paper written by and published by . This book was released on 1994 with total page 102 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Geological Survey Professional Paper written by Geological Survey (U.S.) and published by . This book was released on 1964 with total page 1066 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book U S Geological Survey Professional Paper written by and published by . This book was released on 1984 with total page 642 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Cenozoic Volcanism in the High Cascade and Modoc Plateau Provinces of Northeast California written by Murray Curtis Gardner and published by . This book was released on 1964 with total page 410 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book U S Geological Survey Circular written by and published by . This book was released on 1933 with total page 608 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Geological Survey Circular written by and published by . This book was released on 1983 with total page 954 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Energy Research Abstracts written by and published by . This book was released on 1988 with total page 312 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Emplacement of Silicic Domes and Lava Flows written by Jonathan H. Fink and published by Geological Society of America. This book was released on 1987-01-01 with total page 155 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Cordilleran Section of the Geological Society of America written by Mason L. Hill and published by Geological Society of America. This book was released on 1987 with total page 505 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Earthquakes in the United States January March 1979 written by Carl W. Stover and published by . This book was released on 1980 with total page 496 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Mineral Information Service written by and published by . This book was released on 1967 with total page 572 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Deep Crustal and Mantle Inputs to North Sister Volcano Oregon High Cascade Range written by Mariek Schmidt and published by . This book was released on 2005 with total page 394 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Central Oregon High Cascade Range is an anomalously mafic segment of the Cascade Arc due to ongoing intra-arc extension, which allows most magmas to traverse the crust without stalling and evolving to more evolved compositions. North Sister, a composite volcano in this arc segment, has produced a seemingly monotonous basaltic andesite (52.5-54.0% SiO2) that is depleted in incompatible elements from [aprroximately] 320 ka until 15 ka. This dissertation addresses the volcanic development of North Sister Volcano and deep crustal processes that produced its basaltic andesite. Stratigraphic variation signaling changes in eruptive style, unconformable contacts, 40Ar/39 dating, and geochemical correlations divide North Sister's eruptive history into four stages: (1) the early shield, (2) the subglacial stage, (3) the upper shield stage, and (4) the stratocone stage. Lastly, the north-striking,>1 11-km Matthieu Lakes Fissure (MLF) transected North Sister in three splays. North Sister's eruptive stages correspond to four compositional groups that record a general decrease in compatible elements such as Ni (112 to 35 ppm), while incompatible elements are constant or generally decrease (e.g. Ba 302 to 247 ppm) through time. Isotopic variations at North Sister are small, but systematic; Sr and Nd isotopic ratios become more mantle-like with time. Petrologic modeling places the generation of North Sister's basaltic andesite in the deep crust by a) deciphering upper crustal re-equilibration; b) mixing a primitive, low K tholeiite (LKT) with a silicic, Al-rich partial melt of 5-30 million year old crust; and c) high recharge rates by mantle-derived LKTs and interaction with a refractory crust. The Sr and Nd isotopic ratios of primitive basalts from the Cascade Range define four segments of the arc that reflect separate isotopic reservoirs and mantle melting regimes and correlate with major crustal domains. These segments are 1) north, Mt. Meager to Glacier Peak; 2) Columbia, Mt. Rainier to Mt. Jefferson; 3) central, the North Sister to Medicine Lake, and 4) south, Mt. Shasta to Mt. Lassen. The central segment has Basin and Range in the backarc and is the most restricted in bulk and isotopic composition.

Download or read book Geologic Field Trips in Western Oregon and Southwestern Washington written by Keith Floyd Oles and published by . This book was released on 1980 with total page 262 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Petrography and Petrology of Volcanic Rocks in the Mount Jefferson Area High Cascade Range Oregon written by Robert C. Greene and published by . This book was released on 1968 with total page 60 pages. Available in PDF, EPUB and Kindle. Book excerpt: