Inaug.-diss.--Berlin. / From Neues jahrbuch für mineralogie etc., beilageband IX. Vita. Includes bibliographical references.

Inaug.-diss.--Berlin. / From Neues jahrbuch für mineralogie etc., beilageband IX. Vita. Includes bibliographical references.

Inaug.-diss.--Giessen. / Each plate accompanied by guard sheet with explanatory letterpress. Lebenslauf. "Benutzte literatur": p. [75]-76.

Thesis (M.S.)--University of Missouri-Columbia, 2005. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (July 11, 2006) Includes bibliographical references.

No description available.

Explosive, caldera forming "super-eruptions" (an eruption of VEI 8 or larger, resulting in 1000+ km³ of volcanic ejecta in ignimbrite sheets) are the single most destructive natural disaster native to Earth. Super-eruptions require three elements to occur: 1-crustal magmatic fluxes above background solidification rates, 2-growth of a batholith scale magma chamber, and 3-an eruption trigger. This study addresses these requirements with new petrographic and geochemical analyses and numerical simulations of crustal magma bodies. Crustal magmatic fluxes up to 10x steady-state arc rates are required to form volcanic provinces that host super-eruptions. Super-eruptions can occur in continental hot-spots or rift environments. Why arcs "flare-up" is the subject of active debate. Arcs may follow a regular cycle of lithospheric thickening, delamination, and asthenospheric upwelling (the Andean cycle); alternatively fertilized lithospheric mantle may undergo rapid melting. Targeted sampling (n = 165) of mapped but unsampled mafic and lamprophyric magmas in the San Juan magmatic locus of Colorado, an archetypical ignimbrite province, over three years identified both the lithospheric mantle reservoir and the most primitive San Juan magmas using optical petrography, whole rock geochemistry (n = 50) and Pb, Sr, and Nd isotope geochemistry (n = 32). These mafic magmas more closely resemble the continental lithosphere geochemically. Mixing models based on Energy Constrained Assimilation/Fractional-Crystallization (EC-AFC) indicate that the San Juan magmatism is the product of lithospheric melts and 30-40% crustal assimilation rather than asthenospheric upwelling. The Farallon flat-slab "pre-fluxed" and refrigerated the Colorado lithospheric mantle; removal of that slab at around 40 Ma triggered the SJVF "flare-up." Numerical simulations of crustal magma chamber growth indicate giant magma chambers form when high magma fluxes raise upper crustal temperatures to 300-400 °C at 5-10 km depth. These simulations focus on chamber growth, convection, and cooling at the expense of geometry or chamber mechanical failure with realistic sill-like geometry at the expense of thermal modeling. New 3D finite difference simulations emphasize the importance of geometry on chamber lifespan and crustal heating. A spherical chamber (i.e. model construct) requires 10x the cooling time of a 2km caldera footprint sill of same volume. Increasing sill thickness by 1km can double chamber longevity. Focused intrusions (i.e. 1D modeling) locally produce higher thermal gradients and preserve larger primary basalt volumes. Random intrusions in 3D yield basalt to crust ratios of 3-4:1 (required in the EC-AFC models). Random intrusion in 3D into the upper crust at "flare-up" fluxes ([greater than or equal to]10 km³ per k.y.) elevate average crustal geotherms by 10 °C / km, allowing for growth of batholithic scale magma chambers a wider footprint. Once situated in the upper crust, sub-caldera magma chambers cool inward forming moving crystallization and fluid saturation fronts. If the saturation front propagates faster than the crystallization front, nucleating fluid bubbles have the opportunity to grow, ascend, and collect at the chamber roof. New 2D finite difference models couple magma chamber cooling to fluid production to explore the conditions of fluid escape and collection. Less silicic magma composition, equant geometry, high ambient thermal gradient, and a stock all aid in fluid pocket growth by slowing the advance of the crystallization front (a fluid trap) and triggering saturation at lower fluid concentrations. Fluid pockets that grow to certain sizes ( > 500 m hemispherical bubble) have the potential to trigger an eruption by propagation of a fluid fracture to the surface. This mechanism possibly triggered the eruption of the 5000+ km³ Fish Canyon Tuff as well as smaller, recent eruptions (Pinatubo, El Chichón). Caldera forming super-eruptions occur in regions that meet these three requirements: 1-high magmatic flux, 2-rapid growth to batholithic size, and 3-a delayed eruption trigger. For the SJVF of Colorado melting of the "pre-fluxed" lithosphere provided the magmatic pulse which melted and heated the crust, forming a broad batholith. As magmatism peaked and began to wane, upper crustal magma chambers started to crystallize, exsolving fluids. These fluids ascended, collected, and fractured their way to the surface, triggering the Fish Canyon Tuff and other eruptions. / text

Proefschrift--Amsterdam. / Summary in German. "Stellingen": 2 leaves inserted. "Literatuurlijst": p. 138-141.

Solidified igneous intrusions from originally liquid magma chambers display a large number of different sedimentary features. These features include the gravitational collapse of sidewalls producing slumps and the layering produced by gravitational settling of crystals. In the chamber fluid-dynamic processes such as convection are expected to occur due to cooling at the roof producing dense gravitationally unstable liquid, and the crystallisation of interstitial liquid changing the composition of the remaining liquid possibly reducing the density causing the liquid to rise up. The crystals which form in basaltic magma chambers have a high propensity to be mobilised due to convection and other fluid-dynamic processes including replenishment by a secondary intrusion. Convective mobilisation of plagioclase grains in vertical, tabular intrusions is seen from flat profiles of apparent aspect ratio as a function of dyke width. These flat profiles were formed due to scouring of gravitationally unstable sidewall mushes, and these crystals then become entrained in the convecting liquid. Convection only ceases once the volume of crystals in suspension reaches a critical volume fraction leading to an increase in viscosity, which dampens the vigour of convection. The majority of this study is performing and analysing a number of different experiments to look at the behaviour of different styles of analogue particle piles. Particle piles that are formed of inert, plastic particles are subjected to convection in the particle layer and in the bulk overlying fluid, and different styles of mobilisation depending on the heat flux driving convection and the density profile of the pile are observed. The mobilisation style goes from rolling of particles on the surface, to puffs of particles from the surface being lofted into the interior, followed by large particle fountains and then the entire particle pile being completely disaggregated and lofted into the interior of the chamber as the force driving convection is increased. The initiation of mobilisation can be explained by the fluidisation of a particle pile, whilst the high degrees of mobilisation seen in some high Rayleigh number regimes can be explaining by resuspending particles. In experiments where particle piles have a positive density profile (dense particles overlying low density particles) the underlying low density particles can break through the overlying layer in particle fountains and can be explained by a modified fluidisation parameter. These experiments lack the reactivity and cohesion that realistic crystal piles would have. To try and quantify this, I have also performed a series of experiments looking at the rheology of an ice-sucrose suspension, where ice crystals can sinter and aggregate together. Under sheared conditions the forces required to disaggregate ice aggregates can be calculated, with the viscosity of an ice-sucrose suspension being described by a power-law relationship of shear rate and crystal radius. The particle pile experiments show that mobilisation of equivalent crystal piles in magma chambers should be readily observed. As it is not observed, except in replenished magmatic systems, this suggests that the additional forces coming from cohesion and aggregation in crystal piles prevent mobilisation of magmatic crystals. The replenishment by secondary intrusions can lead to forces which overcome the strength of the pile.

Eocene magmatism in the Great Basin is spatially and temporally associated with major gold mineralization and with the early stages of the westward retreat of magmatism from its eastern-most advance. The Battle Mountain Mining District in north-central Nevada is one of the more prominent areas of Eocene intrusive activity and Au-(Cu) mineralization. The district hosts Jurassic dikes, three centers of Cretaceous magmatism, as well as the major magmatic event of the late Eocene. This study, however, focuses on the youngest of the three events and looks in depth at the Eocene igneous centers across the district and their associated hydrothermal alteration and mineralization. The major areas of late Eocene magmatism and hydrothermal activity are at Elder Creek in the north, Copper Basin in the east, and Copper Canyon in the south, along with the smaller occurrences and deposits such as Buffalo Valley, Modoc, Long Peak, and Timber Canyon. New U-Pb ages on zircons were determined for 38 igneous rocks from around the district. These ages along with the 67 previously published U-Pb, Ar-Ar, and K-Ar ages were used to constrain the timing of emplacement of all of the igneous centers of Eocene age to a contracted period beginning around 42 Ma and ending between 39 and 38 Ma. The internal consistency in the resulting U-Pb ages requires that many of the previous dates in the district, especially the K-Ar ages, should be viewed with caution. Inherited cores were found in the zircons from 37 of the 38 samples analyzed in this study. This includes both abundant Jurassic and Cretaceous cores that are likely derived from older igneous rocks in the subsurface, as well as abundant cores of other ages that resemble but do not fully match the reported detrital zircon populations of the allochthonous sedimentary rocks from the Roberts Mountains and Golconda allochthons. Populations of zircons that are not known from surficial exposures imply that other rocks may be present at depth provided the some of the inherited zircons to the magmas. To better characterize the Eocene magmas, intrusive rocks were analyzed for major and selected trace elements, and their constituent minerals were analyzed by electron microprobe. Rock compositions are broadly calc-alkaline, metaluminous to weakly peraluminous, and range from quartz monzodiorites to high-silica rhyolites, with the majority of the rocks being granodiorites. Based on their titanite + magnetite ± ilmenite mineralogy and the compositions of biotite and hornblende, the igneous rocks are relatively oxidized with average ΔNNO values of +1.16 at 500 bars, +1.74 at 1000 bars and +2.29 at 2000 bars. Aluminum-in-hornblende with plagioclase thermobarometry on mineral rims indicates that the magmas were emplaced in the upper 5 km of the crust. Data from certain phenocryst interiors and from porphyritic dike swarms, however, reflects higher equilibration pressures and may indicate the position of an underlying source at a depth of 10-15 km. Overall these data characterize the Eocene magmatic system over ~10 km vertical extent. Hydrogen isotopic evidence suggests a minimum of two major fluids sources in these hydrothermal systems to explain the origin of the diverse mineralization and alteration in the district. The Na-Ca(-K) types of alteration, which are observed in many parts of the district, suggest there is a large influx of external saline fluids that contained isotopically heavy hydrogen in all of the major Eocene deposits. The range of δD values for all actinolite samples associated with the Na-Ca(-K) types is from -19‰ to -59‰. These values represent a significant shift from the δD values of hydrous minerals in the magmas and in the associated potassic alteration where the range of δD values for biotite is from -35‰ to -82‰, for amphiboles it is from -55‰ to -92‰, and for secondary biotite is from -34‰ to -90‰. The values for unaltered igneous hornblende and biotite are akin to those of magmatic water, whereas the heavier isotopic compositions from actinolite plot in the fields of either basinal brines or metamorphic fluids. In contrast, the sulfur isotopic compositions from these systems are surprisingly homogeneous across the district. Alteration assemblages characterized by petrographic and electron microprobe studies. Alteration of siliciclastic and igneous rocks includes: potassic, sericitic, sodic-calcic, calcic, and potassic-calcic alteration. Two types of skarn occur in the district. Fortitude-type skarns replace carbonate rocks and consist of hedenbergite + diopside + andradite + pyrrhotite with Au+Cu, mineralization whereas Labrador-type, potassic-calcic and calcic-ferric alteration and skarns replace feldspathic, silicic, and carbonate rocks, respectively, and consist of andradite + diopside + hematite + magnetite with Au+Cu mineralization. Taken together, the volume and distribution of these assemblages, along with fluid inclusion data, hydrogen isotope compositions, and petrologic considerations indicate two fluid sources: magmatic fluids generated potassic, sericitic, and Fortitude-type skarns, and moderately saline, non-magmatic fluids produced Na-Ca(-K) alteration mineral assemblages and Labrador-type skarns. Those features inferred to be magmatic-hydrothermal are restricted in their extent and related to particular intrusive phases, whereas the Na-Ca(-K) alteration features typically extend over several kilometers and are not correlated with any particular intrusive phase. Observations within the Battle Mountain district and regionally indicate that a variety of fluids – magmatic and non-magmatic – played significant roles in Eocene intrusion-centered hydrothermal systems. Consequently both fluid types need to be considered in interpreting Cenozoic metallogeny in the northern Great Basin.

Instances of fault-controlled monogenetic volcanism across the subduction arc of the Central Andes at ~ 23°S illuminate the nature of different parental melts being delivered to the crust. Evidence of magmatic history is preserved in bulk rock geochemistry, the content of melt inclusions, and mineral compositions. Volcanism in this region is dominated by felsic and intermediates lavas as the thickened crust (55 – 65 km) and vast volumes (> 500,000 km3) of mid-crustal magma beneath the Altiplano-Puna high plateau region prevent mafic magmas from reaching the surface (Davidson & De Silva, 1991; Beck et al., 1996; Perkins et al., 2016). However, small volumes of relatively undifferentiated lava have been delivered from the lower crust to the surface along zones of crustal weakness without extensive processing by crustal assimilation and/or extended storage in sub-volcanic magma chambers. Monogenetic eruptions of less-differentiated lava provide important constraints on compositions normally obscured by crustal processing in the Central Andes. Basaltic andesite sampled within the frontal arc (Cerro Overo maar) is a regional mafic end-member and approximates the composition of parental arc magmas derived from partially-molten lower crustal regions where mantle-derived magmas interact with the surrounding lithosphere and undergo density differentiation (MASH zones). Basaltic olivine-hosted melt inclusions from Cerro Overo provide a glimpse of less-evolved melt composition from this region and suggest mobilization of MASH magma by injection of basaltic melt. Basaltic andesite sampled from the eastern (back) margin of the frontal arc (Puntas Negras – El Laco) is another regional mafic endmember, representing a mantle-derived magma composition that is transitional between subduction arc magmatism and intraplate magmatism of the back-arc. The internal crystal architecture revealed by major and trace element zoning of olivine phenocrysts indicates Cerro Overo magma experienced continuous ascent, while Puntas Negras magma experienced a brief period of stalling or storage near the brittle-ductile transition zone (~ 25 km). Aphyric intermediate monogenetic lavas sampled west of (before) the frontal arc display Adakite-like signatures (e.g. high Sr/Y and Sm/Yb) represent small amounts of melt generated with a significant contribution from direct melting of the metabasaltic slab or delaminated lithospheric root at high pressure. These three magmatic regimes sampled at monogenetic centers approximate different end-member compositions being delivered to the lower crust of the Central Andes from which the range of intermediate main arc volcanism in the Altiplano-Puna region is ultimately derived.