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Pliocene-Pleistocene sediments in the southeastern Acambay graben, central Mexico have yielded mammal fossils, including Equus simplicidens, cf. Rhynchotherium, ?Camelops, Mammuthus sp., Bison sp., and Antilocapra sp. The fossiliferous sediments include a period of lacustrine sedimentation in the late Pliocene-early Pleistocene that interrupted fluvial and alluvial sedimentation during the early Pliocene and Pleistocene. The sediments deposited in this late Pliocene paleolake record a history of lake level fluctuations, shown by lithologic variations in lacustrine sediments and abundance of vertebrate burrows. Volcanic and tectonic events in the Acambay graben were the major controls on sedimentation during Pliocene-Pleistocene time. Various local volcanic structures produced source rocks for Pliocene-Pleistocene sediments, and intra-arc extensional tectonics caused basin subsidence. Blockage of stream drainages by lava flows or perhaps increased basin subsidence contributed to the appearance of and fluctuations in the lacustrine system during the late Pliocene. Diatom assemblages from lacustrine sediments indicate slightly higher precipitation and humidity than present-day conditions in the Acambay graben. Therefore, climatic forcing may have also contributed to the development of the late Pliocene paleolake in the Acambay graben. Pliocene-Pleistocene volcanic rocks in this part of the Acambay graben range from basaltic andesite to rhyolite. The calc-alkaline composition of these volcanic rocks is similar to others in the modern Mexican Volcanic Belt; they have a continental arc affinity, which is consistent with a tectonic setting within the Mexican Volcanic Belt. The major eruptive episode in the Acambay graben occurred during the early Pliocene, although volcanism, represented by small volcanic structures, continued until the late Pleistocene. This observed decline in volcanism in the Acambay graben correlates with a early Pliocene through Quaternary trenchward migration of volcanism in the Mexican Volcanic Belt.

The Green River Formation was deposited between 53.5 and 48.5 Ma. The Angelo, Fossil Butte, and Lower members of the Green River Formation at Fossil Basin, preserve ash fall tuffs deposited in ancient Fossil Lake. 40Ar/39Ar dating of sanidine yielded eruptive ages of 51.29 ± 1.29 Ma and 52.20 ± 3.08 Ma for two of the tuff beds within Fossil Basin. Immobile element and mineral compositions of Fossil Basin tuffs indicate that most tuffs erupted from a subduction zone originally as rhyolites and dacites. X-ray diffraction analyses reveal that the tuffs' glassy matrices have been altered to illite, calcite, clinoptilolite, analcime, albite, and K-feldspar. The variable alteration of the tuff beds confirms previous studies of Fossil Lake's salinity fluctuation through time. One outcrop (FB-10), which was previously interpreted to represent the K-spar tuff, has biotite of different compositions from that in known K-spar tuff samples (FB-09 and FB-11). Tuff horizons from the Greater Green River Basin have feldspar and biotite compositions similar to those from tuffs in Fossil Basin and are interpreted to have the same eruptive sources. Based on age and proximity, the Absaroka and Challis volcanic fields are the likely sources of tephra deposits in Fossil Basin and the Greater Green River Basin. Calc-alkaline tephras in these lacustrine basins have similar magmatic characteristics to the tuff of Ellis Creek (48.4 ± 1.6 Ma) from the Challis volcanic field. However, major and trace element, and mineral compositions of Absaroka and Challis volcanic rocks are not distinctive enough to definitively determine the source of most Fossil Basin and Greater Green River Basin tephras. Two samples, FB-10 from Fossil Basin and WN-79.15 from the Greater Green River Basin, have compositions similar to calc-alkaline magmas, but have some mineral compositions with A-type chemical affinities; consequently we conclude that they were erupted from volcanoes within the Challis volcanic field. Compositions of Challis volcanic rocks may have important implications for the development of a slab window in western North America during the Eocene. Compositional variation of Challis volcanic rocks through time indicates that calc-alkaline rocks with a slight A-type component erupted early in its history, and as the slab window matured the Challis volcanic field dominantly erupted rocks with a more A-type chemical affinity. A slab window may have developed due to the Farallon slab subducting at a shallow angle beneath the North American plate, and gravity may have caused it to break to the north. Through time the slab could have torn to the south and by 50 Ma the slab window would have been opening beneath the Challis volcanic field. This would have erupted calc-alkaline magmas, but upwelling of the asthenosphere into the mantle wedge (beneath the North American plate) would have introduced A-type magmatism into the magmatic system. By 45 Ma, the slab would have matured and opened sufficiently beneath the Challis volcanic field to replace calc-alkaline magmatism with, first "transitional" magmatism, and then A-type magmatism as evident in the youngest Challis tuffs.

The Wah Wah Springs Tuff (30.0 Ma) is one of several very large volume ash-flow tuffs (>3200 km³ of erupted magma) that were emplaced near the peak of the flare-up of activity in the Great Basin ignimbrite province of western North America. It can be characterized as a "monotonous intermediate" ignimbrite because of its intermediate concentrations of silica (~63 to ~70 wt. %), apparent uniform chemical and mineralogical characteristics, and crystal-rich nature (32 ± 10 % phenocrysts on a dense rock basis). The major phase assemblage found throughout deposit is similar to other monotonous intermediates with a few exceptions (pl > hnbl > bio, qtz >> cpx, opx > mt, ilm, ap, zcn, and po). Based on experiments on the monotonous intermediate Fish Canyon Tuff (Johnson & Rutherford, 1989a) and this phase assemblage, the Wah Wah Springs magma equilibrated between 775°C – 800°C. One hornblende-plagioclase thermometer with or without quartz (Holland & Blundy, 1994) and one Fe-Ti oxides thermometer (Anderson et al., 1993) most consistently yield temperatures within this range. The Fe-Ti oxides oxy barometer (Anderson et al., 1993) yield fO2 estimates 2 – 3 log units above the quartz-fayalite-magnetite buffer. The Al-in-hornblende geobarometer (Johnson & Rutherford 1989b) indicates pressures between 2.0 and 2.5 kb. Detailed compositional profiles across hornblende and plagioclase grains help constrain how intensive parameters changed during the evolution of the magma shortly before eruption. Plagioclase in the Wah Wah Springs displays oscillatory zonation with overall normal zonation (a maximum change of about An5 from core to rim). Hornblende is also zoned in Al2O3 and TiO2 which typically decrease as much as 2.5 wt. % and 1 wt. % respectively from core to rim. These zoning patterns are consistent with a decrease of temperature from core to rim that accompanied progressive crystallization of a large body of magma that closely approached equilibrium. These conditions in the parent magma for the Wah Wah Springs differ from interpretations of mineral compositions in the Fish Canyon Tuff which led Bachman et al., (2002) to propose that the near solidus magma body was "rejuvenated" or reheated immediately prior to eruption. This model cannot be applied to the Wah Wah Springs. Rather, the Wah Wah Springs magma appears to have been cooling and crystallizing prior to eruption.

Geologic structures within the Birdseye 7.5 minute quadrangle Utah County, Utah have been related by previous workers to both the Jurassic Arapien Shale diapirism and to the mid-Cenozoic extensional collapse of the Charleston-Nebo Thrust. Whichever model proves valid, it will have implications for oil exploration and interpretation of the subsurface geologic structure in the region. A detailed map of the quadrangle was constructed to better constrain which mechanism was responsible for the deformation. Exposures of Arapien Shale near, and within the Birdseye quadrangle show no evidence of diapiric movement. Arapien involvement in the deformation of Tertiary rocks in the center of the quadrangle is therefore unlikely. Changes in the pattern of sedimentation of Eocene age rocks suggest a change in tectonics during this time. Restoration of the Eocene strata shows that the most plausible mechanism for this deformation is extension along reactivated thrusts in the Arapien Shale, Thaynes Formation, and Woodside Shale, related to Basin and Range extension. The Moroni Formation, a prominent Tertiary volcanic unit present throughout the Birdseye quadrangle, has been used to justify Eocene extension. Deformation with the formation was found to be present only along the Thistle Canyon normal fault, constraining movement along the fault to the Eocene and later. Dip and facies relationships present within the formation mainly are a result of paleotopography rather than extension. Several distinctive units were mapped within the formation, including lahar and fluvial deposits, as well as two different ash-flow tuffs. A depletion in nickel and chromium, an unusually ferroan composition, and distinctive Fe/Ti ratios suggest that the volcaniclastic rocks of the Moroni Formation are similar to volcanic rocks in the Slate Jack Canyon and Goshen quadrangles which lie about 35 km to the west. This implies that the ignimbrites and volcanic clasts in the Moroni Formation were sourced from the East Tintic volcanic center. It further implies that any mid-Tertiary extension between the East Tintic center and the Birdseye quadrangle did not create barriers to sedimentation and was limited in extent.

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第21968号 / 農博第2358号 / 新制||農||1070(附属図書館) / 学位論文||R1||N5219(農学部図書室) / 京都大学大学院農学研究科地域環境科学専攻 / (主査)教授 北山 兼弘, 教授 小杉 緑子, 教授 舟川 晋也 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DGAM

Forecasts of short term volcanic activity are generated using an event tree process that is driven by a set of empirical statistical models derived through logistic regression. Each of the logistic models are constructed from a sparse and geographically diverse dataset that was assembled from a collection of historic volcanic unrest episodes. The dataset consists of monitoring measurements (e.g. seismic), source modeling results, and historic eruption information. Incorporating this data into a single set of models provides a simple mechanism for simultaneously accounting for the geophysical changes occurring within the volcano and the historic behavior of analog volcanoes. A bootstrapping analysis of the training dataset allowed for the estimation of robust logistic model coefficients. Probabilities generated from the logistic models increase with positive modeling results, escalating seismicity, and high eruption frequency. The cross validation process produced a series of receiver operating characteristic (ROC) curves with areas ranging between 0.78 - 0.81, which indicate the algorithm has good predictive capabilities. In addition, ROC curves also allowed for the determination of a false positive rate and optimum detection threshold for each stage of the algorithm. The results demonstrate the logistic models are highly transportable and can compete with, and in some cases outperform, non-transportable empirical models trained with site specific information. The incorporation of source modeling results into the event tree’s decision making process has begun the transition of volcano monitoring applications from simple mechanized pattern recognition algorithms to a physical model based forecasting system.

Geochemistry plays a vital role in our understanding mechanisms behind major geological systems such as the Earth's crust and its oceans (Albarède, F. 2003). More recently, geo-chemistry has played a vital role in the field of forensic investigation and in period dating. Forensic soil samples have been traditionally analysed via examinations of colour, texture and mineral content by physical or chemical methods. However, these methods leave any organic or water-soluble fractions unexamined. Tephrochronology (the dating of sedimentary sequences using volcanic ash layers) is an important tool for the dating and correlation of sedimentary sequences containing archives and proxies of past environmental change. Its importance in this area has increased since the increased free carbon in out atmosphere has made radio-carbon dating unreliable. Tephrochronology requires successful geo-chemical identification of the tephras, a method reliant on electron probe micro-analysis (EPMA) to analyse major element composition. However, it is often impossible to differentiate key tephra layers using EPMA alone. Raman spectroscopy is commonly used in chemistry, since vibrational information is specific to the chemical bonds and symmetry of molecules, and can provide a fingerprint by which these can be identified. Here, we demonstrate how Raman spectroscopy can be used for the successful discrimination of mineral species in tephra through the analysis of individual glass shards. We further demonstrate how, with the use of oxidative preparation methods, Raman spectroscopy can be used to successfully discriminate between soil types using mineralogy as well as the organic and water-soluble fractions of soils.

<p> A series of shallow intrusive and extrusive silicic volcanic rocks near Mamainse Point, Ontario, were sampled and analyzed for major and trace elements. The rocks are mainly fine grained, silicified rhyolites grading to dacites containing phenocrysts of quartz and feldspar. The analyses performed (XRF, AAS) indicate that many of these rocks have been altered from the normal igneous spectrum of rocks to potassic keratophyres. An enrichment in potash from potash metasomatism has accompanied low grade, burial metamorphism to produce a secondary mineral assemblage including chlorite, carbonate, and sericite. Local intense alteration of some rocks involved the depletion of mobile alkalis and addition of water and co2 to form calcite and kaolin. The overall field and chemical evidence suggest a single magmatic source for these rocks. </p> / Thesis / Bachelor of Arts (BA)

<p> Freegold Mountain is part of a northwesterly trending volcanoplutonic arc comprising the eastern portion of the Yukon Crystalline Terrane. Plutonic rocks in the area intrude Paleozoic metasediments and consist of a Late Triassic to Early Cretaceous granodiorite intruded by the Big Creek Syenite dated at 138 ± 10 Ma. A suite of K-rich intrusive volcanic rocks comprise an early period of basalt-andesite-dacite volcanism and a later rhyolitic volcanism dated at 78 ± 6 Ma. Volcanic rocks at Freegold Mountain can be correlated with Mt. Nansen Volcanics.</p> <p> Two sets of fracture planes, oriented at 165/70E and 18/80W, show dextral and sinistral displacement, respectively. Rhyolite dykes and gold-quartz veins predominantly oriented NNE have been emplaced along the 18/80W extensional fracture systems. These fractures may be modelled as high-angle Reidel shears, although evidence indicates that fracture orientations and fault movement have been complicated by changing stress fields from middle Cretaceous to Tertiary time.</p> <p> The gold-bearing quartz veins at Freegold Mountain are high grade, low-tonnage deposits with grades ranging from 0.4 to 1.0 oz/t. Fluid inclusions from the lower portions of the Laforma mine homogenize at 185° C with salinity ranging between 2 and 4.5 wt. % NaCl equivalent. A boiling zone has been detected above the deeper ore where fluid inclusions show extreme ranges in homogenization temperatures (165-430° C) and salinity (4 - 43 wt. % NaCl). Fluid inclusion waters have stable isotopic signatures indicative of meteoric water with 𝛿D = -138 and 𝛿^18O = -18.4. Boiling of the Laforma fluid has caused a shift towards heavier hydrogen and oxygen isotopic values, mineral deposition and appears to enhance gold precipitation over non-boiling zones. Stable isotopic evidence indicates that the paleolatitude of Freegold Mountain during late Cretaceous time was south of the present day Yukon-B.C. border.</p> <p> The Emmons Hill (Dart) prospect is a gold-bearing vein-breccia with a mineral assemblages of barite, stibnite, marcasite, cinnabar, orpiment, Fe and Mn carbonates and chalcedonic silica. Fluid inclusions from these deposits homogenize between 140-185° with salinities of 0-0.5 wt. % NaCl. This property shows marked similarities to acid-sulphate type precious metal deposits in New Zealand and western United States.</p> <p> Large (x to xx Mt) northwesterly trending diatremes appear to be structurally controlled by small transcurrent faults parallel to and coeval with displacement along the Tintina fault. The Antoniuk diatreme (3.7 Mt @ 1.14 g/t Au) consists of heterolithic and monolithic breccias intruded by dacite and rhyolite dykes. Diamond drilling indicates that a large body of fine to medium grained alaskite is present beneath the auriferous breccia. The deposit formed by the explosive escape of volatile components evolved from the retrograde boiling of a silicic magma chamber. Gold mineralization in the breccia is associated with pyrite and arsenopyrite formed at temperatures around 300°C and salinities of about 4.5 wt. % NaCl.</p> / Thesis / Master of Science (MSc)