High-pressure to ultrahigh-pressure metamorphism of Pohorje eclogites : master thesis = metamorfoza pohorskega eklogita v visokotlačnih do ultravisokotlačnih pogojih : magistrsko delo
Vrabec, Mirijam
Kyanite eclogites from the Pohorje Mountains, Slovenia, are providing the first evidence of ultrahigh-pressure Eo-Alpine metamorphism in the Eastern Alps. Polycrystalline quartz inclusions in garnet, ...omphacite and kyanite are surrounded by radial fractures and exhibit microtextures diagnostic for the recovery after coesite breakdown. The non-stoichiometric supersilicic omphacites found in Pohorje eclogites contain up to 5 mol % of Ca-Eskola molecule. Such clinopyroxenes are known to be stable exclusively at high-pressure conditions exceeding 3.0 GPa. Their breakdown during decompression resulted in exolution of quartz rods and needles that are oriented parallel to omphacite c-axis. The absence of coesite is a consequenceof near-isothermal decompression during the first stages of exhumation. Pressure and temperature conditions for the formation of the peak metamorphic mineral assemblages have been assessed through a consideration of a) Fe2+-Mg partitioning between garnet and omphacite pairs, based on differentcalibrations; b) the equilibrium between garnet+clinopyroxene+phengite kyanite quartz/coesite assemblage. Estimated peak pressure and temperature conditions of 3.0-3.1 GPa and 762-839°C are well within the coesite, i.e. the ultrahigh-pressure stability field. The continental crustal rocks of the Lower Central Austroalpine unit of the Pohorje Mountains were subducted to depths of at least 90-100 km, indicating that UHP metamorphism occurred in the Alps also during Cretaceous orogeny. The southward increase in peak pressures from approximately 2 GPa in the Koralpe and Saualpe to 3 GPa in the Pohorje suggests the south to south-eastern dip of the Cretaceous intra-Alpine subduction zone.
Type of material - master's thesis
; adult, serious
Publication and manufacture - Ljubljana : [M. Vrabec], sep. 2004
Geologija M VRABEC Mirijam High-pressure IN: 000013829
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