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- Title
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.
- Authors
Németh, B.; Török, K.; Kovács, I.; Szabó, Cs.; Abart, R.; Dégi, J.; Mihály, J.; Németh, Cs.
- 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 a clinopyroxene-plagioclase vein and patches with primary silicate melt inclusions (SMI). The samples have non-equilibrium microtexture in contrast with the 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 and the fluid and melt inclusion study suggest that at least three fluid events occurred in the deep crust represented by these xenoliths. 1. Primary CO-dominated ± CO ± HS fluid inclusions were observed in the wall-rock part of Sab38 xenolith. 2. The crystallization of new clinopyroxene from melt, with CO + HO fluid. 3. The crystallization of new plagioclase occurred in a heterogeneous fluid-melt system with additional N and CH 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.
- Subjects
GARNET; GRANULITE; MELTING; VOLCANIC fields; PLEISTOCENE Epoch; INCLUSIONS in igneous rocks; UPLANDS; THERMOMETRY
- Publication
Mineralogy & Petrology, 2015, Vol 109, Issue 2, p217
- ISSN
0930-0708
- Publication type
Article
- DOI
10.1007/s00710-015-0366-6