Marin, Marco (2015) Deformazione del granato in eclogiti UHP della Norvegia. [Laurea triennale]
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In south-western Norway emerges the Western Gneiss Region, an area generated during the Paleozoic through the Caledonian orogeny. The tectonic event begins approximately 490Ma during the Ordovician, and ends at 400mA in the Lower Devonian. In this thesis we analyzed two samples of eclogites from this metamorphic region. The samples come from mafic material of the continental crust, reaching subduction to depths greater than 100km. The peak in eclogite facies is reached at 760 ° C and 3.0GPa. Rocks shows a series of mineralogical associations, containing garnet, plagioclase, biotite, clinopyroxene. Garnets in the rocks are characterized by very stretched and deformed aspect. Optical microscope shows a mosaic structure constituted by the presence of many grains at sub-millimeter scale. The SEM analysis providing insight into the microstructure and the EBSD is used to observe the deformation process that has interested the garnet. With a microscopy is evident that the garnet is present in mosaic structures, with grains united by joints triple and regular limits. Inside the grains are absent secondary mineral phases, there is no zoning chemistry and there is a edge of decomposition in amphibole around the mosaic. Results of EBSD indicate has been active the mechanism of grain boundary sliding, that causes a random orientation of the crystal lattice with each other. The microstructures also suggest that they may have been active mechanisms of ductile deformation, such as dislocation creep.
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