Proefschrift--Utrecht, 1958. / Summary in French and Dutch. Bibliography: p. 116-118.

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This study aims to develop a robust research methodology to examine the evolution of magmatic volatile phases during the cooling of felsic magmas via detailed melt- and fluid-inclusion studies, in particular the investigation of inclusions originally containing both melt and aqueous fluid. Then, using these techniques I will examine fluid immiscibility processes in two felsic magmatic systems, one mineralised, the other barren. In particular, I address the constraints on the exsolution of magmatic vapour and aqueous liquids, and how it is manifested in quartz-hosted inclusions, as well as the nature and composition of the exsolved phases. In developing a research philosophy two factors need to be paramount, it needs to be as widely applicable as possible, and the limitations need to be recognised and explored. Thus, the results deriving from these techniques may provide a test of the methodology. The thesis is based on two case studies, Rio Blanco (Chile) and Okataina (New Zealand). The first case study involves sub-volcanic intrusives and associated extrusives from the La Copa Rhyolite, and intrusives from the Don Luis Porphyry, two post-ore rhyolitic suites from the Los Bronces-Rio Blanco Porphyry Cu-Mo deposit. The second case study involves rhyolitic lavas (< 65 Ka) from the Okataina Volcanic Centre in the Taupo Volcanic Zone in New Zealand. This study is not intended to examine the geology of these systems, but rather to use them as examples of felsic systems, in diverse tectonic settings. Both as test cases for developing robust research techniques and for any information that they can provide regarding late-stage magmatic processes, particularly volatile phase exsolution, and the role of melt/fluid and liquid/vapour immiscibility. At Rio Blanco, the melt inclusion populations consist predominantly of glass inclusions and coexisting dark, inhomogeneous crystalline silicate melt inclusions (CSMI's). An important discovery from this study is the recognition that CSMI's trap volatile-rich melt, probably identical to the melt trapped as glass inclusions, and are crystallised, not "devitrified" or the product of post-magmatic alteration. Heating experiments demonstrate that both the glass and CSMI's from Rio Blanco have decrepitated and degassed post-trapping, notwithstanding the apparent lack of petrographic indicators of degassing in the glass inclusions. This coexistence appears to be a common occurrence; however, its significance seems to have been overlooked in a number of previous studies. From an initial volatile-rich melt, aqueous volatile phases (dominantly vapour) exsolved, forming bubbly magmatic emulsions. Inherently, magmatic emulsions are metastable, and disrupt into discrete melt and vapour phases. The vapour-rich phases separated from the melt and escaped, cooling, condensing, and mixing as they did so. Rio Blanco melt inclusions and fluid inclusions trapped all of these phases, in various combinations, both demonstrating the process in fine detail, and sampling the phase compositions. Analysis of the phases demonstrates partitioning of metals (Cu, Zn, and possibly Pb) into the vapour phase, its transport out of some of the magma bodies, and implies concentration by mixing and condensing to form metal-rich hypersaline fluid inclusions in the carapace of the Don Luis Porphyry. The Okataina case study provided an invaluable counterpoint to Rio Blanco. Phenocryst crystallisation pressures were supercritical, although the evidence suggests that volatile phase exsolution (VPE) occurred post- rather than pre-trapping, so that trapped magmatic emulsions are not observed. Okataina also contains coexisting CSMI's and glass inclusions, although many of the samples contains a complex array of partly crystalline silicate melt inclusions. Importantly for this study, many of the inclusions do homogenise during experimental heating, indicating that decrepitation and degassing were not as pronounced as at Rio Blanco. Heating experiments showed that despite coexisting CSMI's and glass inclusions, there was only a single melt trapped. This provides evidence of the post-trapping behaviour of melt inclusions, lacking at Rio Blanco. Although pre-trapping VPE did not occur to a large degree, post-trapping VPE did. Inclusions in which exsolution of an aqueous volatile phase has occurred provide a measure and sample of the amounts of fluids that were exsolved from a known quantity of melt, and may provide a method of determining the actual amounts of hydrothermal fluids that a magma body may exsolve. In evaluating these results some inevitable limitations of the techniques have been uncovered, particularly those relating to the vagaries of melt inclusion formation and preservation, and these have been evaluated. However, qualitative, and to some extent quantitative results have been produced, some of which have been published in research journals. Together, the case studies demonstrate and sample the fine detail of the exsolution of volatile-rich phases from silicate melts, their escape from those melts, and eventual cooling and condensing to form the kinds of hypersaline hydrothermal fluids found as fluid inclusions in ore-bodies. Further, they provide insights into common post-trapping behaviours of melt inclusions, some aspects of which appear to have been misinterpreted in some published melt inclusion studies.

Proefschrift--Amsterdam. / "Samenvatting": p. [ix]-xiii. "Stellingen": ([3] p.) inserted. "Literature": p. [164]-165.

Inaug.-Diss.-Münster (Westf.). / Lebenslauf. Includes bibliographical references (p. [7]).

Thermobarometry, detailed petrography, electron microprobe analysis, and fluid inclusion microthermometry were used to quantify the history of a high grade Proterozoic terrane exposed within the northeastern Colorado Front Range. Pressure-temperature calculations identified two blocks from different crustal levels exposed adjacent to one another within the Poudre Canyon west of Fort Collins. They are the eastern, higher pressure, block (HPB; 734 degree C, 7.1 kbar) and the western, lower pressure, block (LPB; 655 degree C, 5.2 kbar). The blocks followed a clockwise uplift path and were juxtaposed by ductile shear near the end of the decompressive stage of uplift. Final assembly of the separate blocks to the same crustal level was constrained by mineralogic and textural considerations and by the isochores of identical low density carbon dioxide inclusions trapped by both blocks. Both blocks experienced peak metamorphism within the sillimanite-K-feldspar zone accompanied by partial melting, are characterized by stromatic migmatites, and show textural evidence for localized reactions related to decompression and cooling. Differences between the blocks include the type of melt-generating reactions and the pronounced late muscovite in the LPB. Gibbs' Method calculations indicate that local (outcrop scale) textural and mineralogical differences between HPB Mg-enriched pelites are caused by small differences in bulk composition and locally variable H2O content. The quartzo-feldspathic biotite gneisses in the LPB generated migmatites by wet melting, whereas the pelitic schists and gneisses in the HPB generated migmatites by dehydration melting of muscovite and biotite. Biotite dehydration melting enriched the leucosomes in HPB pelitic migmatites in K-feldspar and garnet. The minor presence of late muscovite in the HPB relative to the LPB was controlled by the different positions of their uplift paths relative to the muscovite breakdown reaction. / Ph. D.

Very high temperature (>900 °C) contact metamorphism and metasomatism of aluminous schist xenoliths in the mafic to ultramafic Cortlandt Complex, New York, resulted in formation of bodies of unusual Fe- and Al-oxide-rich rock called emery. During contact heating, disequilibrium thermal decomposition of the protolith schists in one closely examined xenolith produced two end-member materials: a quartzo-feldspathic water-undersaturated melt which partitioned much of the silica and calcium and all of the alkalis of the original schist; and a highly aluminous fine-grained emery residuum which contained spinel, magnetite, ilmenohematite, sillimanite, and sporadically corundum. During cooling, melt within the xenoliths was injected as cm-scale veinlets into the silica-poor solid residuum. Local increase in silica activity resulted in progressive silication reactions of spinel-rich residuum to several silicates. A simple model of progressive silication would require that reactions should occur from lower to higher silica content of product silicates in stages, e.g., spinel – sapphirine (Si/O=0.10), sapphirine – garnet (0.25), garnet – orthopyroxene (0.28), rather than directly from spinel to higher-silica minerals which would overstep intermediate reaction steps. However, observed reaction textures indicate the latter more complex behavior in which spinel may have reaction rims of, or occur as inclusions within, any of the three silicate minerals. Statistical analysis of several samples has shown the mode to be the spinel-orthopyroxene reaction rim boundary although orthopyroxene is the highest-silica product mineral, based on Si/O ratio. Chi-square test results are significant and show that the textural relations observed among spinel, sapphirine, garnet, and orthopyroxene are dependent. Increased silica activity therefore cannot be the only factor controlling the reaction sequence. Microprobe data has been collected in an attempt to correlate mineral compositions with the different textural occurrences. The effects of local equilibria appear to be the dominant factors in the overstepping of sequential reactions. Qualitative activity-activity diagrams proved useful for examining the effects of bulk composition on the relative stabilities of spinel and the three silicates, including variations in Fe/(Fe+Mg), bulk Mn and Zn contents, and minor local variation in oxygen fugacity. Matrix spinel compositions (i.e., those not modified by reaction to silicates) fall into two groups: a more magnesian one containing spinels with average Fe/(Fe+Mg) (Fe#) of 0.49 and a less magnesian one, average Fe# of 0.67. With regard to this bulk compositional effect, the more magnesian composition should reduce garnet stability due to the strong fractionation of Fe into garnet, thus favoring the reaction of spinel to orthopyroxene within silica-rich areas. In more aluminous areas, spinel will react to form sapphirine, then garnet, then possibly orthopyroxene. A less magnesian composition would expand the stability of garnet at the expense of sapphirine and, to a lesser extent, orthopyroxene. Zinc has a subtle effect on mineral stabilities. Because Zn is strongly partitioned into spinel, higher zinc contents (concentrations in some spinels are as high as 14.9 mol% gahnite) may expand the stability of that mineral considerably. Consequently, spinel stability may increase relative to the three silicates, but this may be quite variable due to variable reaction stoichiometry and different reaction-boundary slopes in the activity-activity diagram. In general, spinels with the highest Zn content occur next to orthopyroxene (ave. 4.9 mol% gahnite in spinels) for which the stability appears to be only slightly affected by this increase in Zn. The greatest decrease in silicate stability is observed in sapphirine. Spinels adjacent to sapphirine contain no more than 1.3 mol% gahnite. The effects of manganese and oxygen fugacity were also examined. Mn increases the stability of garnet due to strong partitioning of Mn into this mineral. It can be inferred using statistical and chemical data that this has some bearing on textural relations in garnet-bearing samples, but the lack of obvious Mn fractionation by other minerals examined makes it impossible to interpret the effects of Mn in the garnet-free samples. Calculated ferric-ferrous ratios in analyzed minerals were examined in an attempt to study the effect of oxygen fugacity on the stabilities of minerals. In the more magnesian compositions, which may correlate with slightly higher fO2 during reactions, spinels should react to form sapphirine, then possibly garnet or orthopyroxene with further silica activity increase. In lower-fO2 environments (perhaps those with higher bulk Fe#), spinel should react directly to form orthopyroxene. The coexistence of magnetite and ilmenohematite dictates T-fO2 conditions very nearly at those of the Hematite-Magnetite buffer. Minor fO2 variations that might have had an effect on silicate-forming reactions would only be recorded by small variations in magnetite and ilmenohematite solid solutions (ulvospinel and ilmenite contents, respectively). These data were not acquired in this study, however, so no definite conclusions could be made. / Master of Science

This dissertation investigates the evolution of continental orogenic systems in Central Asia during and between pre-collisional plate convergence (Cordilleran-style orogenesis), syn-collisional plate convergence (collisional orogenesis), and post-collisional tectonic processes within the scope of closing Paleo-Asian and Tethyan ocean basins. A brief introductory chapter outlines the scope and context of the research. Appendix A focuses on the Late Paleozoic closure of the Turkestan ocean basin and subsequent collision between the Karakum–Tarim and Kazakh–Kyrgyz terranes in the South Tian Shan, within the scope of the final amalgamation of the Mesoproterozoic–Permian Central Asian Orogenic Belt. Appendix B focuses on late Cenozoic syn-collisional exhumation of gneiss domes in the India–Asia collision, which is a component of the Triassic–recent Alpine–Himalayan orogenic belt. Abstracts of the results are provided in the respective appendices.

The results of a combined mineral equilibria and fluid inclusion study show that the Manhattan Prong, southeastern New York, has experienced multiple metamorphic events. Two episodes of intrusion, separated by approximately 100 million years, have superimposed contact aureoles on the Taconic regional metamorphic gradient in the northeastern Manhattan Prong and have modified the regional assemblage to different degrees. The assemblage Sil-Bt-Grt-Qtz-Pl+Ksp+Ms in regionally metamorphosed Manhattan Schist records P-T conditions of 4-5 kbar and 650-700 oC. Garnet porphyroblasts, homogenous with respect to major elements but zoned with respect to P and Y, contain ubiquitous, primary, CO2-rich fluid inclusions which have a Th = 10-24 oC. Manhattan Schist collected adjacent to the Croton Falls and Peach Lake mafic complexes, intrusions thought to be related to the Late Ordovician Cortlandt Complex, record P-T estimates of 4 kbar and 700 oC and 4.2 kbar and 550-600 oC respectively. The lack of fluid inclusions in garnet porphyroblasts indicates that the regional metamorphic assemblage has been completely modified by the contact effects of the mafic intrusions. However, the presence of Ky+Sta along with the slight compositional zoning of garnets in Peach Lake samples suggests that the contact assemblage may have been modified by a later metamorphism. Manhattan Schist collected adjacent to ~350 Ma granites (Brock, 1993) has been partially modified by contact metamorphism and shearing but vestiges of the regional metamorphic assemblage remain. Garnet porphyroblasts contain abundant CO2-rich fluid inclusions and P-T estimates using Bt and Pl inclusions and garnet core compositions are similar to estimates of regional metamorphic conditions. Evidence of modification includes garnet overgrowths that are elevated in Ca and depleted in Mn, Y and Sc, and CO2-rich fluid inclusions that have reequilibrated to higher density (Th = 2-18 oC). Rim compositions of porphyroblasts yield P-T estimates of 5-6 kbar and 550-600 oC. The elevated Ca content of the overgrowths along with the presence of Ky in the matrix suggests that the reaction An = Ky + Grs + Qtz may have been active during the overprinting metamorphism. The increase in pressure recorded in the granite aureoles in the Manhattan Prong is inconsistent with the results of P-T studies of the Rowe-Hawley belt, approximately 20 km to the east across Cameron's Line. This suggests that these two terranes may have been separated in the Devonian. / Master of Science