Metamorphic hydrous, CO2-bearing fluids play a critical role in the global carbon cycle. However, how big this influence is on the global carbon cycle and therefore on global climatic processes, is unknown. The actual amount of CO2 which is released into the atmosphere due to metamorphic processes is still debated. For this purpose, fluid-driven reactions in metamorphic rocks must be studied by tracking fluid-rock interactions along pathways of ancient fluids. In the study presented in this thesis, we study fluid-rock interaction in the southeastern part of the Greek island Syros in the Cycladic Archipelago (Aegean). On Syros fluid-rock interaction is recorded by the preservation of blueschist facies assemblages at greenschist facies conditions along a normal shear zone. Blueschist preservation is caused by a combination of metasomatic addition of SiO2 and Na2O and elevated XCO2 which is maintained by high fluxes of a CO2-bearing, hydrous fluid along the shear zone. This research aims to provide a better understanding of the role of mountain building in the carbon cycle. Flux estimates for climate-forcing fluid components (e.g. carbon) require that their concentration in the fluid, fluid volumes and velocities are known. This will be the focus of future work. Further, whole rock chemistry and the availability of specific minerals will be studied to achieve knowledge about which kind of parameters influence and enhance the propagation of fluids through rocks.

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

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Geology and Geophysics, 1967. / Vita. / Bibliography: leaves [179]-[187]. / by William Howard Blackburn, Jr. / Ph.D.

No description available.

Sensing systems for mid-infrared wavelengths (2 to 5 μm) have important applications in biomedical, atmospheric and process gas monitoring systems. For lack of a suitable substrate, the full potential of GaSb-based materials, which are particularly suitable for operating in these wavelengths, are not completely realized. Hence, metamorphic growth technology, that allows the growth of semiconductor epilayers of arbitrary composition on any substrate, has been explored for antimony materials in this research. This makes the growth of device layers, containing arbitrary composition of GaSb-based materials, possible on commercially available 6"-GaAs substrates, and thereby reducing fabrication cost. Metamorphic growth of In(0.15)Ga(0.85)Sb was achieved using gas-source molecular beam epitaxy by growing compositionally graded ln(x)Ga(1-x)Sb buffer layers on a GaSb substrate. The effects of growth temperature on the quality of the metamorphic buffer layers along with the etching issues (both wet and dry) of GaSb-based materials were studied. Homo-junction n-i-p and p-i-n diodes were fabricated on In(0.15)Ga(0.85)Sb metamorphic layers. The dark current and its temperature dependence were measured and the extraction of area and perimeter components of dark current was done. The modeling of the components of dark current suggests that the diode currents were dominated by surface leakage. Surface passivation by silicon nitride and polyimide were investigated and our findings suggest that the former resulted in a better passivated surface. Responsivity measurements show that In(0.18)Ga(0.82)Sb diodes, metamorphically grown on GaSb substrates, have a cut-off wavelength of 2270 nm. Finally, hole (β) and previously unreported electron (α) ionization coefficients, at room temperature and 90° C, were extracted from these structures. The results show that α>β for ln(0.10)Ga(0.90)Sb for both temperatures. These photodetectors can be implemented m practical receiver systems for mid-infrared applications, such as atmospheric CO2 and methane detection at 2.0 μm. The possibility of growing antimony-based device layers on larger substrates, paves the way for future optoelectronic receiver systems operating at longer wavelengths, where both the photodetector and the amplifier can be integrated in the same module. / Thesis / Doctor of Philosophy (PhD)

<p> Oxygen and hydrogen isotopic distributions have been studied for rocks from a 100 km transect in the central Superior Province of Ontario, Canada. The transect represents progressively deeper terrains of the Michipicoten Greenstone Belt (MGB), the Wawa Gneiss Terrane (WGT), and the Kapuskasing Structural Zone (KSZ), which correspond to an increase of metamorphic grade and are interpreted as an oblique section through approximately 20 km of crustal thickness. The rocks in the terrains range in age from ~2.76 to ~2.60 Ga, with fewer later intrusions.</p> <p> Equivalent lithologic types have similar δ18O range at middle and lower crustal levels (WGT and KSZ). Tonalitic to granodioritic rocks range from 6.4%o to 9.5o/oo; Dioritic and anorthositic rocks range from 5.5o/oo to 7.6o/oo; a majority of the mafic gneisses (group 1) range from 5.7o/oo to 7.1o/oo, while group 2 mafic gneisses range from 8. 1o/oo to 9.5o/oo. δ18O values of the rocks exhibit a remarkable correlation with SiO2 values, similar to that observed in unaltered plutonic rocks of equivalent composition. Paragneisses have significantly higher δ18O values, 9.3o/oo to 12.2o/oo. Low-grade metavolcanic and metasedimentary rocks of the MGB are 18O-enriched compared to their high-grade equivalents in the KSZ and WGT, 7.4o/oo to 13.3o/oo for mafic to felsic metavolcanic rocks and 11.4o/oo to 14.7o/oo for clastic metasediments.</p> <p> Coexisting minerals from high-grade rocks exhibit 18O-fractionation closely consistent with isotopic equilibrium, suggesting that the isotopic system has not been grossly disturbed. Isotopic thermometers give uniform apparent temperatures, about 553°C to 584°C, across the entire transect, which are lower than the inferred metamorphic temperatures in the highest-grade (KSZ) terrane.</p> <p> The lack of distinctive isotopic differences between equivalent rock types in the KSZ and WGT suggests that there is no significant gradient in δ18O with depth in the crust or with metamorphic grade. The majority of mafic gneisses (Group 1) have δ18O values similar to fresh basalts and appear to have been emplaced either as subaerial extrusives, intrusive sills, or, less likely, as submarine extrusives that were hydrothermally altered at high temperatures. The less abundant Group 2 mafic gneisses have δ18O values typical of greenstones that were altered at low temperature by sea-water, and isotopically resemble low-grade rocks in the Michipicoten and Abitibi belts. In general, no major changes in whole-rock isotopic composition appear to have occurred during granulite facies metamorphism, implying limited flux of water or CO2.</p> <p> The continuous linear gradient in δ18O vs SiO2 in the high-grade rocks cannot be due to differentiation of a mafic source magma. A model involving an association between mantle-derived mafic magma and 18O-enriched crustal materials is more consistent with the oxygen isotopic data.</p> <p> Hydrogen isotope composition of hornblende and biotite has been analyzed from selected rocks. Mafic and anorthositic rocks from the KSZ have δD values from -58 to -62o/oo, suggesting a possible mantle-derived origin of fluid in the system. Two mafic gneisses, which are 18O-enriched, show lower δD values, -89 and -101o/oo. The depletion of deuterium is consistent with the model of low temperature alteration with seawater in a submarine environment. Mafic and tonalitic gneisses from the WGT are also depleted in deuterium, -87 to -109o/oo. Since these rocks intruded into relatively higher level of the crust and commonly contain secondary alteration minerals, it is possible that hydrothermal alteration took place at late- or post-metamorphism stage, and the source of the fluid is likely meteoritic water, The amount of water involved in the exchange was restricted, and was not enough to disturb the oxygen isotopic system in the rocks.</p> / Thesis / Master of Science (MSc)

This thesis is missing either page 57 or 58. The other copies of this thesis do not have this page either. -Digitization Centre / This study is an investigation of two regions which were once part of the same Proterozoic margin: the Frontenac Axis in the Southeastern Grenville Province of Ontario, and the island of Islay in Scotland. Shieh (1985) performed an oxygen isotopic study on the granitic plutons and surrounding metasediments in the Frontenac terrane. For the granites south of the Rideau Lake Fault, he observed extremely high 18O/16O ratios of +14.0%o (relative to SHOW), whereas north of the fault, the plutons gave ratios of around 10%o. Five of the plutons in Shieh's study have been dated using U-Pb zircon geochronology, with the following results: Battersea -1165 ± 3 Ma, Lyndhurst -1166 ± 3 Ma, Perth Road -1166 ± 3 Ma, Crow Lake -1176 ± 2 Ma, and Westport -1076 ± 2 Ma. The zircon ages are younger than the depleted mantle Nd model ages obtained (1211 to 1480 Ma) and signify that the plutons may be derived from a mantle source with contamination by the older surrounding metasediments which have an average Nd model age of 1790 Ma. Correlation between initial Nd (ENd(t) from +1 to +3) and initial Sr (Esr(t) from +9 to +21) also shows a mixed origin for the plutons. However, oxygen isotopes show that contamination by marble may also have occurred. Two features distinguish the Frontenac terrane southeast of the Rideau Lake Fault (RLF) from the Central Metasedimentary Belt (CMB) to the northwest: 1) the anorogenic (i.e. within plate) chemical signatures of the plutons, which are similar to the Hid-Proterozoic anorogenic granites that occur throughout North America (Anderson, 1983); and 2) the unique zircon ages for the plutons south of the RLF (1166 to 1176 Ha) that occur nowhere else in the CMB. This implies that the two areas define different crustal terranes. However, since Penokean (ca. 1800 Ha) crustal extraction ages are found in both terranes they may represent displaced segments of a single Penokean continental margin. In Scotland, a gneiss terrane on Islay was always inferred to be part of the Archean Lewisian complex. However, isotopic evidence shows that the Islay terrane is early Proterozoic in age (1782 Ha by U-Pb zircon geochronology) and that it is juvenile mantle-derived material, not a reworking of Archean crust during the Proterozoic. As a result, two major implications for the crustal evolution of Northern Britain are: 1) the Grampian terrane, an area directly adjacent to the newly defined Proterozoic Islay block, is probably underlain by Proterozoic basement; and 2) Northern Britain can be included in the Lower Proterozoic reconstruction of the Laurentian Shield. The similar crustal extraction ages observed in the Grenville of Ontario and on Islay give proof that these areas were part of a major 1.8 to 1.9 Ga crustal formation event, stretching from the southwestern U.S. to Finland. / Thesis / Master of Science (MS)

The timing, duration, and pressure-temperature (P-T) conditions of metamorphism provide a direct record of the physical and chemical evolution of the crust and inform our knowledge and understanding of plate tectonics. The characteristic timescales and length-scales of metamorphism vary by orders of magnitude, depending on the driving tectonic process. Two fundamental problems with the retrieval of this information from the metamorphic rock record are insufficient temporal resolution and processes that overprint or obscure the full record of metamorphism. Understanding what processes are recorded, and why they are recorded, is critical for accurate models of tectonics. This dissertation examines these processes in the metamorphic rock record in two settings: the central Appalachian orogen and the Western Alps fossil subduction zone. Chapters 2 and 3 focus on poly-metamorphic migmatites from the Smith River Allochthon (SRA) in the central Appalachians. A combination of petrography, thermodynamic modeling, and geochemistry is used to document and quantify the metamorphic evolution of the SRA and determine the petrologic processes that control metamorphic re-equilibration in high-temperature metamorphic systems. Chapter 2 presents new constraints for Silurian high-temperature (~750℃, 0.5 GPa) contact metamorphism in response to mafic magmatism and a cryptic Alleghanian metamorphism (~600℃, 0.8 GPa). A combination of extensive and highly variable melt loss followed by H2O-flux melting during contact metamorphism is shown to produce a range of modified bulk rock compositions and domains with variable fertilities for metamorphic re-equilibration during the Alleghanian. In chapter 3, monazite, allanite, and zircon laser ablation split-stream petrochronology are used to constrain the timing of poly-metamorphism and develop a tectonic model for the SRA. The SRA preserves evidence for at least three orogenic events, each with a relatively short duration (< 10 Myr.), likely due to repeated magmatic heating. The full record of this punctuated heating is obscured by dissolution-reprecipitation reactions that variably recrystallize monazite and decouple trace element chemistry from isotopic age and significantly restrict equilibrium length-scales. Chapters 4 and 5 examine the dynamic interplay between transient fluid flow, episodic metamorphism, and deformation in subduction zones. In chapter 4, diffusional speedometry is applied to eclogite breccias from the Monviso ophiolite to quantify the periodicity of transient deformation and metamorphism at eclogite facies P-T conditions. The maximum timescale for repeated fracturing is constrained to ~1 Myr., likely caused by cyclic variations in fluid pressure and strain rate (not necessarily seismicity). While difficult to preserve and detect in the rock record, this periodic metamorphism may play an important role in detachment and exhumation processes in subduction zones worldwide. Finally, in chapter 4 a combination of thermodynamic modeling and Sm-Nd garnet geochronology are used to construct a model for subduction and exhumation of the Voltri ophiolite. Garnet growth occurs rapidly and close to peak P-T conditions (~520℃, 2.4 GPa) across the ophiolite, with large (>10 km2) areas preserving near-identical ages, suggesting that the Voltri ophiolite was exhumed as several large coherent units, aided by the presence of buoyant serpentinites. / Doctor of Philosophy / Metamorphism provides a direct record of the physical and chemical evolution of Earth's crust and informs our knowledge and understanding of how plate tectonics works on Earth. Differences in the physical conditions (e.g. pressure, temperature) and timescales of metamorphism can provide clues for the operation of unique tectonic processes, such as the intrusion and cooling of magma deep underground or the collision of two tectonic plates and formation of a mountain range. The key is to correctly "read" the metamorphic rock record. One inherent difficulty in reading and interpreting metamorphic rocks is that few current methods are able to resolve very short timescale events (much less that 1 million years (Myr.) in duration), such as earthquakes, in the rock record. Moreover, metamorphic rocks experience numerous distinct 'events', which partly overprint one another and produce a complicated and near impossible puzzle for geologists to unravel. Solving this puzzle is critical to fully understand how plate tectonics works on Earth. This dissertation addresses these problems and examines metamorphism in two locations: the core of the ancient supercontinent Pangea (central Appalachians) and a fossil subduction zone (the Western Alps). Chapters 2 and 3 focus on the central Appalachians. Chemical and textural analysis of metamorphic rocks are used to understand the major heat sources that operated in the crust during the formation of the Appalachians and determine the processes that control metamorphic re-crystallization at extremely high temperatures. Chapter 2 presents new constraints for high-temperature (~750℃) metamorphism in response to magmatic heating and provides evidence for a younger metamorphic event that is cryptically recorded. A combination of compositional changes caused by earlier high-temperature metamorphism and the later addition of water along reactive grain boundaries are shown to be important factors in the cryptic record of the younger metamorphic event. In chapter 3, U-Pb geochronology is used to the determine the timing of metamorphism and construct a tectonic model for the central Appalachians, which preserves evidence for at least three tectonic events over ~200 Myr, but with each occurring over a relatively short duration (< 10 Myr.). These events are interpreted to represent repeated magmatic heating 'pulses' during the formation of Pangea. However, the full record of this punctuated heating is partly obscured by subsequent fluid alteration. Chapters 4 and 5 examine the dynamic interplay between transient fluid flow, earthquakes, and metamorphism deep in subduction zones. In chapter 4, fracture sets within metamorphic garnet crystals from the French Alps (Monviso) are used to determine the timescale of repeated fracturing and recrystallization during subduction. The fracture timescales are estimated to be much less than 1 Myr. and are interpreted to record repeated fluid "pulses" and possibly deep earthquakes. While difficult to preserve and detect in the rock record, this process may play an important role in bringing metamorphic rocks back from deep in subduction zones to Earth's surface. In chapter 4, a combination of mineral chemistry and geochronology are used to construct a tectonic model for the subduction and exhumation of a portion of the Italian Alps (Voltri). Metamorphic reactions occur synchronously and immediately before exhumation across a wide area (> 10 km2). This suggest that large (> 10 km2) pieces of oceanic crust can metamorphose, detach, and exhume deep in subduction zones.

Microstructural data on the orientation and distribution of minerals can be utilized to better understand the processes controlling mineral crystallization during metamorphism and the extent to which equilibrium versus kinetic factors control the evolution of metamorphic rocks. Four studies in this dissertation address this, finding that: i) garnet crystals crystallize via epitaxial nucleation in which garnet crystallizes by templating on the crystal structure of muscovite; ii) the distribution of grain boundary void space at quartz-quartz and garnet-quartz grain boundaries is a function of the orientation of quartz crystals on either side of the grain boundary. There are more voids, and in some cases larger voids, at grain boundaries in which the a-axis of a neighboring quartz grain is perpendicular to the grain boundary than any other orientation; iii) the chemical potentials of garnet-forming components evolve differently in samples in which garnet growth either significantly or minimally overstepped equilibrium garnet-forming reactions; iv) the southwestern Meguma Terrane, Nova Scotia, experienced peak metamorphic conditions of ~630ºC and 4.0 kbar, likely resulting from regional metamorphism during the Neoacadian orogeny. A case study on the mechanisms controlling garnet crystallization in one Nova Scotian sample reveals that the rate limiting step of garnet crystallization was probably the diffusional transport of Al through the intergranular matrix. Taken together, this work has implications for understanding: i) the properties of grain boundaries in metamorphic rocks and ii) the extent to which equilibrium versus kinetic factors impact metamorphic petrogenesis. / Doctor of Philosophy / A fundamental question in the development of metamorphic rocks, or rocks that form due to changes in pressure and temperature conditions deep in the Earth's mountain belts, is: what controls the crystallization of new minerals? While pressure, temperature, and bulk composition likely play a major role in this, it is also possible that the distribution of reactant minerals and the transport of elements through the rock may also play a role in mineral crystallization. This dissertation explores several projects related to this broad topic. In one example, garnet, an important metamorphic mineral, was found to crystallize by utilizing the atomic structure of another mineral in the rock. This creates a favorable pathway for the crystallization of garnet, which preferentially grows on this 'parent' mineral. Further, the distribution of porosity, or void space, at the interfaces between mineral grains in metamorphic rocks is found to be controlled by the orientation of those minerals. This porosity likely formed when the rocks were exhumed from deep in the Earth towards its surface. Metamorphic rocks can also tell the story of continental plates colliding millions of years ago. In an example from the formation of the Appalachian Mountains ~400 million years ago, a combination of collisional tectonic forces and the heat from magmas in the shallow crust resulted in metamorphic rock, which make up much of southern Nova Scotia today. This work has important implications for understanding: i) porosity in metamorphic rocks and ii) how minerals crystallize during metamorphism.

Garnet porphyroblasts are commonly used to determine P-T conditions in metamorphic rock assemblages. However, the actual process of porphyroblast nucleation is still poorly understood and garnet growth may occur at different conditions than those predicted by equilibrium thermodynamics. It is typically assumed that the Gibbs free energy of a system can be used to predict the growth of garnet at a given P and T, but here a new idea is proposed that in nature, growth does not occur until the chemical potential of each garnet-forming component departs from its equilibrium (pre-nucleation) state. Similar thermodynamic modeling results from a variety of metamorphic settings, rock types and apparent degrees of overstep indicate these deviations likely control the extent of overstep in the garnet-forming reaction in many natural samples. The process of metamorphic differentiation is then used to explain microstructures observed in the Haimanta Group, NW India that contain quartz-rich and mica-rich layers, with numerous garnet porphyroblasts appearing solely in the quartz-rich layers. This process is deformation-controlled, allowing the microstructures to be used as kinematic indicators to determine the deformation history of the Haimanta Group. The Elle Microstructural Modeling Program, the Basil deformation code and observed chemical zoning of garnets are used to prove metamorphic differentiation as the process responsible for garnet growth, meaning a singular, prograde event resulted in garnet growth in the Haimanta Group, in agreement with published monazite data for theses samples. / Master of Science