Academic literature on the topic 'Rocks, Metamorphic'

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.<br>Doctor of Philosophy<br>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.

Geometric analyses of three mylonite zones, including two metamorphic-core-complex SC-mylonite zones, show that the mylonitic foliation surfaces (S-surfaces) are consistently discordant to the margins of the shear zones. Finite-strain analyses show that the foliation surfaces in each zone are consistently oriented parallel to the XY-plane of the finite strain ellipsoid. The shear bands within the mylonites (C-surfaces, C'-surfaces, extensional crenulations, and shear-band cleavages) are uniformly oriented subparallel to the margins of the shear zones. The finite lengths and discontinuous natures of the shear bands require that the displacement along them be accommodated by the S-surfaces at the tips of the shear bands. Thus the S-surface elongations and orientations represent the total bulk rock strain, rather than some minimum measure of inter-C-surface strain. General stress and strain considerations indicate that the shear bands are planes of maximum shear stress, and that they are not only simple-shear slip planes. This interpretation implies that in simple-shear deformation, a single, irrotational set of shear bands will develop parallel to the shear-zone boundaries. In deformations involving significant components of coaxial strain, however, shear bands may develop in other orientations or in conjugate sets and rotate with progressive deformation.

Fluids, mainly H2O and CO2, are released from H- and C-bearing phases during prograde metamorphism. Because of the buoyancy of these fluids, they rise within the crust towards the surface of the Earth. Metamorphic fluids take advantage of permeable horizons, shear zones, fold hinges, fractures, and are channelled into high-flux zones. Fluid fluxes for channelized fluid flow may exceed background pervasive fluxes by several orders of magnitude. Metamorphic fluids react with the surrounding rock during fluid flow, and altered zones are commonly observed adjacent to high-flux conduits. Fluid-altered rock is texturally, mineralogically, chemically, and isotopically different from rock unaffected by fluid flow. In this thesis, fluid-rock interaction is studied at two localities in the Scottish Highlands: Glen Esk and the Isle of Islay. Glen Esk is one of the type localities used by George Barrow (1853-1932) to propose the concept of metamorphic zones and metamorphic index minerals as an approximate determination of metamorphic grade. In several of the metamorphic zones in Glen Esk, index mineral distribution is highly dependent on proximity to veins. The occurrence of index minerals is therefore not only controlled by pressure and temperature, but also by the availability of metamorphic fluids. Evidence of a retrograde fluid flow event from the North Esk Fault is observed in Glen Esk, for which a time-averaged fluid flux of 0.0003 – 0.0126 m3∙m-2∙yr-1 is calculated. The duration of the fluid event is estimated to between 16 and 334 kyr. On the Isle of Islay, kyanite is observed in rocks of chlorite or lower-biotite metamorphic grade, i.e. much lower temperatures than usually associated with kyanite formation. The favoured explanation for this is retrograde infiltration of extremely high-CO2 fluids, at least locally XCO2 &gt; 0.7, at ~340°C, which altered these rocks and stabilised kyanite in a carbonate-bearing assemblage. Oxygen and carbon stable isotope profiles across the Islay Anticline reveals highly channelized fluid flow along the axial region of this fold, with fluid:rock ratios at least four times higher than in rock farther away from the fold. Although carbon and oxygen isotope ratios of metacarbonate rocks were altered along the Islay Anticline, negative anomalies observed below and above the Port Askaig Tillite Formation cannot solely be attributed to metamorphic fluid flow, which implies that these rocks to varying degree retain their primary paleoclimatological isotopic signatures.<br>Stora volymer H2O och CO2 frigörs som fluider under prograd metamorfos. Metamorfa fluider har lägre densitet än det omgivande berget, varför de stiger genom jordskorpan mot jordytan. Metamorfa fluider kanaliseras i permabla lager, skjuvzoner, veckaxlar, sprickor och andra högflödeszoner. Kanaliserade fluidflöden kan vara flera storleksordningar högre än bakgrundsvärdet för fluidflöde inom en bergart. Metamorfa fluider reagerar under transport med det omgivande berget och bildar fluidomvandlade zoner i anslutning till högflödeskanaler. Fluidomvandlat berg uppvisar texturella, mineralogiska, kemiska och isotopsammansättningsmässiga skillnader i jämförelse med berg som inte utsatts för fluidomvandling. I denna avhandling behandlas reaktioner mellan fluid och berg som studerats i två lokaler i de skotska högländerna: Glen Esk och Islay. Glen Esk är en av de typlokaler som George Barrow (1853-1932) använde för att lägga fram konceptet om metamorfa zoner och metamorfa indexmineral som används för att ungefärligt uppskatta metamorf grad. I flera av de metamorfa zonerna är förekomsten av indexmineral i hög grad beroende av närhet till kvartsådror, vilket visar att bildandet av indexmineral inte bara styrs av tryck och temperatur, utan också av åtkomst till metamorfa fluider. I Glen Esk finns också spår av ett fluidflöde från North Esk-förkastningen, under retrograda metamorfa förhållanden, för vilket mededfluidflödet över tid uppgår till 0.0003 – 0.0126 m3∙m-2∙år-1. Denna fluidflödeshändelse beräknas ha pågått mellan 16 000 och 334 000 år. På ön Islay i de sydvästra högländerna återfinns bergarter, som trots sin låga metamorfa grad i klorit- eller biotitzonen innehåller mineralet kyanit, dvs. temperaturer långt under vad som vanligen associeras med kyanitbildning. Detta förklaras med infiltration av fluider med extremt hög CO2-halt, åtminstone lokalt så högt som XCO2 &gt; 0.7, vid ca. 340°C. Fluidomvandling av dessa bergarter stabiliserade kyanit tillsammans med karbonatmineral. Syre- och kolisotopprofiler över Islayantiklinen påvisar hög kanalisering av fluider längs dess veckaxeln. Förhållandet mellan fluid och berg var mer än fyra gånger så högt i närheten av veckaxeln jämfört lokaler längre ifrån densamma. Påverkan av metakarbonatbergarters isotopförhållanden har skett längs Islayantiklinen, men fluidpåverkan kan inte ensamt förklara de isotopanomalier som observerats under och ovan Port Askaig-tilliten, varför dessa bergarter kan ha bibehållit sin primära paleoklimatologiska isotopsignatur.<br><p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: Manuscript.</p>

Appendix 4 and 5 in pocket on back cover. Bibliography: p. 123-130. The isotopic data indicates the Harts Range Metamorphic Complex formed within a previously unrecognized intracratonic tectonic province in Central Australia