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

Many of the large igneous provinces during the Phanerozoic have been temporally linked to mass extinction events. The intrusion of magma into country rock has been hypothesized to facilitate the release of carbon and sulfur bearing volatiles and has been proposed as one of mechanisms that drove these mass extinctions. In this study I examine a dike of the Central Atlantic Magmatic Province and its interaction with adjacent sedimentary rocks in the Culpeper Basin of Virginia. Sampling was done at the 0.5 m scale along transects of sedimentary lithologies perpendicular to the ~170 m wide diabase intrusion. The observed mineralogical and geochemical changes in sedimentary rocks occur in a much narrower zone from the intrusion than predicted by the applied thermal model. Carbon isotopes of organic matter within the sedimentary rocks are enriched in 13C toward the intrusion indicating the generation of thermogenic methane within the first meter from the intrusion. Additionally, geochemical and petrologic textures suggest both the addition of magmatic sulfur into the country rock, shown through the isotopic signatures of sulfide minerals with mantle compositions. The possible thermal break down of sedimentary pyrite is evidenced by highly negative isotopic composition of sulfide minerals and general lack of pyrite. I suggest that sedimentary pyrite initially reacted to pyrrhotite, which was then converted to chalcopyrite through reactions with copper in fluids derived from the magma. These reactions also allowed for the formation of magnetite, which is elevated near the dike-sedimentary contact and at the end of the transect. A simple illustrative model of a hypothesis of fluid flow along the bed is used to explain the observed isotopic signatures and mineralogical changes along the transect. This study highlights how models for volatile generation through magma-country rock interaction may have overestimated the volatile fluxes from these environments and the roles that heterogeneity of sedimentary rocks and kinetic factors may have in the variance in these fluxes. / Master of Science

Krkonose-Jizera plutonic complex is one of the largest composite plutonic bodies in the Czech massif. The emplacement of this pluton relates to the origin of the structural and thermal aureole. The processes of contact metamorphism are most evident in the northern and southern part. The topic of this work is to find influence of the contact metamorphism in the host rocks. Partial information about contact metamorphism in this area could be found in several papers, but there aren't work which discuss this topic in detail. Goal of this work is to make complex interpretation of contact metamorphic processes connected with intrusion of the Krkonose-Jizera plutonic complex and use this interpretation for discussion about model of magma intrusion. In rocks of contact aureole of Krkonose-Jizera plutonic complex (KJPC) were identified relicts of Variscan regional metamorphism, connected to creation of regional metamorphic fabric S1 and S2. Original mineral associations and deformation fabrics were in near-contact zone of KJPC 1 km in average in width heterogeneously overprinted by effects of the contact metamorphism, which intensity increases towards the intrusive contact. In the mineral associations of contact-metamorphic rocks appears characteristic minerals such as cordierite and andalusite, rarely...