Petrology and thermobarometry of eclogite rocks in the Krasnaya Guba dike field,belomorian mobile belt |
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| Authors: | V M Kozlovskii L Ya Aranovich |
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| Institution: | 1.Institute of the Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry (IGEM),Russian Academy of Sciences,Moscow,Russia |
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| Abstract: | A sequence of mineral associations was examined in eclogitized basites of the Krasnaya Guba dike field in the Belomorian Mobile
Belt. Two morphological types of eclogite and eclogite-like rocks were recognized: (1) eclogite rocks that developed after
ferrogabbro dikes and completely replaced these dikes from contact to contact and (2) eclogite-like rocks that developed after
gabbronorites in zones of ductile deformations and shearing. According to data mineral geothermobaromety, both rock types
were formed within temperature and pressure ranges corresponding to high-pressure and high-temperature amphibolite facies
at T = 700 ± 40°C and P = 10.0 ± 0.5 kbar. The peak metamorphic parameters of the host gneisses are analogous. The decompressional stage, which is
unambiguously identified by reaction textures, occurred at 630–660°C and 7.9–8.2 kbar. As the temperature and, first of all,
pressure decreased, the SiO2 activity in the fluid systematically varied. The eclogitization of the basites took place locally in relation to fluid fluxes,
which were restricted to zones of intense deformations, at variable SiO2 activity. The rocks show evidence of two stages of post-eclogite amphibolization. Older amphibolization 1 was coeval with
the late prograde metamorphic stage (T = 650°C, P = 10–11 kbar). Younger amphibolization 2 affected eclogitized basite dikes and unaltered gabbronorites (together with their
host gneisses) over large areas. This process coincided with decompression (T = 580°C, P = 7–8 kbar) and was likely accompanied by the exhumation of deep zones of BMB to upper-middle crustal levels. |
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