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Melting, fluid migration and fluid-rock interactions in the lower crust beneath the Bakony-Balaton Highland Volcanic Field: a silicate melt and fluid inclusion study

Németh, Bianka and Török, K. and Kovács, István János and Szabó, Csaba and Abart, R. and Dégi, Júlia and Mihály, Judith and Németh, Csaba (2014) Melting, fluid migration and fluid-rock interactions in the lower crust beneath the Bakony-Balaton Highland Volcanic Field: a silicate melt and fluid inclusion study. Mineralgy and Petrology. (Submitted)

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Abstract

Plio-Pleistocene alkali basalt hosted mafic garnet granulite xenoliths were studied from the Bakony- Balaton Highland Volcanic Field (BBHVF) to trace fluid-melt-rock interactions in the lower crust. Two unique mafic garnet granulite samples were selected for analyses (optical microscopy, microthermometry, electron microprobe, Raman and IR spectroscopy), which contain clinopyroxene-plagioclase vein and patches with primary silicate melt inclusions (SMI). The samples have non-equilibrium microtexture in contrast with overwhelming majority of previously studied mafic garnet granulite xenoliths. Primary silicate-melt inclusions were observed in plagioclase, clinopyroxene and ilmenite in both xenoliths. The SMI-bearing minerals located randomly in Mi26 and in a clinopyroxene-plagioclase vein on the edge of Sab38 granulites. Petrography, fluid and melt inclusion study suggests that at least three fluid events occurred in the deep crust represented by these xenoliths. 1. Primary CO2-dominated±CO±H2S fluid inclusions were observed in the wall-rock part of Sab38 xenolith. 2. The crystallization of new clinopyroxene from melt, with CO2+H2O fluid. 3. The crystallization of new plagioclase occurred in a heterogeneous fluid-melt system with additional N2 and CH4 during crystallization. A local reaction was observed between sphene and acidic melt, which formed ilmenite+clinopyroxene+plagioclase±orthopyroxene. The ‘water’ content of the rock forming minerals was determined by infrared spectroscopy. The calculated bulk ‘water’ content of the Mi26 xenolith is 171±51 ppm wt. %. The bulk wall rock part of the Sab38 granulite contains 55±17 ppm wt. % of ‘water’, whereas the bulk plagioclase-clinopyroxene vein contains 278±83 ppm wt. %. These results imply a very dry lower crust, locally hydrated by percolating fluids and melts.

Item Type: Article
Subjects: Q Science / természettudomány > QE Geology / földtudományok > QE02 Geochemistry / geokémia
Q Science / természettudomány > QE Geology / földtudományok > QE06 Petrology. Petrography / kőzettan, petrográfia
Depositing User: Dr. István János Kovács
Date Deposited: 24 Sep 2014 12:06
Last Modified: 24 Sep 2014 15:47
URI: http://real.mtak.hu/id/eprint/16441

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