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Showing 1 to 20 of 56 for “"Andesite"”.
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The timescales of andesite generation at Mount Ruapehu, New Zealand
Intermediate composition arc volcanoes present some of the most serious natural hazards because of their tendency towards violent, explosive eruptions. Very little is known about the long term processes which produce such magmas and the timescales over which they operate. U-series systematics have …
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A field, petrologic, and geochemical study of the Callahan Lava Flow, a basaltic andesite for Medicine Lake Shield Volcano, California
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1985.
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PETROLOGIC AND GEOCHEMICAL ANALYSIS OF INTERMEDIATE TO MAFIC MAGNETITE-BEARING VOLCANIC FLOWS AND ASSOCIATED DIKES IN THE KNIGHT RANGE, GRANT COUNTY, NEW MEXICO
… magnetite in two mapped units (the JPM Mountain Andesite; the Malpais Latite and Andesite). In these units, magnetite is disseminated and found in a foliated texture in areas of presumed fluid alteration near joints.</p> <p>Samples of the Proterozoic diabase dikes, the JPB Mountain Andesite, the …
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Petrography of Four Rock Units Exposed in the Campbell Red Lake Mines, Ontario
… four main rock units recognized at the mine: “andesite”, “altered rock”, “siliceous rock”, and “Campbell diorite”. These units have been presumed to be igneous in origin and intruded by lamprophyre, quartz-feldspar porphyry, and grey dikes. Samples of the four rock units were taken from the …
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Geochemical and petrological investigation into the magmatic system at Soufrière Hills Volcano, Montserrat.
Andesite lavas from the current eruption of the Soufrière Hills Volcano, Montserrat exhibit evidence for magma mingling, related to the intrusion of mafic magma at depth. The processes of mass transfer and flux of material involved in the interaction between mafic and silicic magmas are crucial for …
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Origin of net-veined and mixed-magma ring intrusions
… compositional range and is dominated by basaltic-andesite and andesite. Detailed petrographical and geochemical (major, trace element and strontium isotope) analyses show these intrusions represent commingling of highly evolved tholeiitic magmas ranging from ferrobasalt through basaltic-andesite …
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Petrogenesis of Eocene-Oligocene magmatism of the Sulphur Springs Range, central Nevada: The role of magma mixing
… ranges compositionally through rhyolite, dacite, andesite and basaltic andesite but is less alkaline than the Bingham volcanic suite. However, the alkali content of the Sulphur Springs suite is similar to other Eocene igneous rocks along the Carlin Trend. The unusual geochemical signature of the …
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Magmatic processes that generated the rim andesites of Medicine Lake Volcano, N. California
… the compositionally distinctive high-Na andesite lavas at Medicine Lake Volcano that erupted at ~100 ka and that built most of Medicine Lake's caldera. These high-Na lavas define a compositional trend that formed by fractional crystallization in a shallow magma chamber (~ 4 to 8 km). …
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Evidence From High Ni Olivine For Diverse Primitive Magmas In Cascade Volcanism
… and northern California, primitive basaltic andesite from central and southern Oregon, and for primitive andesite from northern California and southern British Columbia. Phenocrysts in nearly all samples show normal core-to-rim compositional zonation, with no evidence for significant …
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Deciphering the Signature of Magma Mixing: Examples from the Castle Creek Eruptive Period, Mount St. Helens, Washington
… On limited occasions, the volcano has produced andesite lava flows, and during one short-lived period, basaltic lava flows. This time interval has been termed the Castle Creek eruptive period and occurred between approximately 2500 and 1700 years B.P. The Castle Creek period erupted dacite, …
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Petrogenesis of the False Bay dyke swarm, Cape Peninsula, South Africa
… from olivine-tholeiite basalt to ferro-tholeiite andesite. This thesis presents detailed field observations of each dyke in the False Bay - Cape Peninsula region and the focus of the study is on the finer details of the differentiation process to define combined assimilation and fractional …
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Permeability modifying processes : thermal cracking and crack healing of geomaterials
… of thermal cracking experiments was performed on andesite plugs from the geothermal field in Awibengkok, Indonesia. Permeability (k) and specific storage capacity were measured by the oscillating flow method in a wide range permeameter, at room temperature, with effective pressures between 15 MPa …
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Stratigraphic and Geochemical Insights into Explosive Volcanism in Northwestern Nicaragua: Case Studies from the Momotombo-Monte Galán Volcanic System and Cosigüina Volcano
… Early erupted dacite pumice and later erupted andesite scoria was sampled at fine scale and a combination of multiple geochemical approaches were applied to characterize matrix glass, plagioclase phenocrysts, and melt inclusions. The textures of the sampled clasts were also characterized using …
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Geologic setting, Mineralization, and Detailed Underground Mapping of the Fire Creek Low-Sulfidation Epithermal Gold-Silver Deposit, Nevada
… veins (Type I ore) hosted in a Miocene basaltic andesite hypabyssal intrusive rock locally known as Tertiary equigranular basalt (Tbeq). The most recent development and mining has focused on ore associated with intense argillic alteration, fault gouge, and abundant sulfides. This refractory and …
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Volcanic stratigraphy and lithochemistry of the lower Jurassic Hazelton group, host to the Eskay Creek precious and base metal volcanogenic deposit
… recorded by fine elastic sedimentary rocks; andesite - hiatus 1 - dacite - rhyolite - dacite - hiatus 2 (peak alteration and 21 Zone mineralization) -basalt. Volcanism occurred in an extensional basinal environment. Consistent mineralogy, calc-alkaline affinities and fractionation trends, …
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THE PETROLOGY AND GEOCHEMISTRY OF HIGH CASCADE VOLCANICS IN SOUTHERN WASHINGTON: MOUNT ST. HELENS VOLCANO AND THE INDIAN HEAVEN BASALT FIELD (TRACE ELEMENT, ISOTOPES, MINERALOGY)
… The major and trace element compositions of some andesites and dacites are broadly consistent with their derivation from a basaltic andesite parental magma by fractional crystallization processes involving the observed phenocryst assemblages. However, the strontium and oxygen isotopic compositions …
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The contribution of manganese oxides to redox buffering in selected soils of the South African Highveld
… lacked the expected redoximorphic features. The andesite soils collected as a sample of intermediary Mn content greater than the quartzite and granite but less than the vertic and dolomite soils also showed an appreciable TED. Results from the study show that the dolomite derived soils, with …
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Evolution of a small silicic system: The McCullough Pass Caldera, Clark County, Nevada
… The topographic high prohibited Hidden Valley andesite, which erupted from a cinder cone field surrounding the McCullough Pass caldera, from flowing into the caldera. After volcanism had ended, preferential erosion of the McCullough Pass rhyolites produced the present topographic low known as …
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The Muddy Creek Formation: Depositional environment, provenance, and tectonic significance in the western Lake Mead area, Nevada and Arizona
… in the Muddy Creek Formation are composed of andesite, dacite, basalt, rhyolite, quartz monzonite, and granite. Paleocurrent data for the basal River Mountain conglomerate suggest that the transport direction was to the southeast, parallel to the regional strike of high-angle normal faults. …
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