Clays and Clay Minerals, Vol. 60, No. 1, 1–17, 2012.
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Authors
Miron, George Dan
Neuhoff, Philip S.
Amthauer, Georg
Issue Date
2012
Type
Article
Language
Keywords
Periodicals , Geology , Chlorite/smectite , Low-temperature Hydrothermal Metamorphism , Prehnite , Pumpellyite , Romania , South Apuseni Mountains , Zeolites
Alternative Title
Low-temperature Hydrothermal Metamorphic Mineralization Of Island-arc Volcanics, South Apuseni Mountains, Romania
Abstract
The island-arc volcanics situated in the eastern part of the Capılnas-Techereu nappe (South Apuseni Mountains, Romania) were studied to evaluate the temperature, fluid properties, and mineral chemistry during low-temperature metamorphism. Detailed observations of metamorphic mineral assemblages were conducted using powder X-ray diffraction and electron microprobe. The metamorphism involved albitization of plagioclase feldspar and the formation of mafic phyllosilicates, zeolites, and other hydrous Ca-Al-silicate minerals. Mafic phyllosilicates consisted of transitional dioctahedral-trioctahedral smectites, mixed-layer chlorite-smectite (C/S, 6-96% chlorite), and discrete chlorite. The zeolites were analcime, stilbite - stellerite, heulandite, laumontite, epistilbite, and mordenite. Also present, as secondary minerals filling amygdales and veins, are prehnite, pumpellyite, and secondary amphibole. Two mineral assemblages were identified which provide important information about metamorphic conditions (temperature, reaction progress, and fluid properties): (1) heulandite + analcime + quartz; and (2) laumontite + albite + quartz + prehnite + pumpellyite - amphibole. The types of and relations between minerals in the first assemblage suggest the occurrence of low-temperature hydrothermal metamorphism in the zeolite facies at ~125ºC, whereas the second assemblage was metamorphosed at 200ºC. The composition and variability of the mineral assemblages in the study area suggest that, due to slow reaction rates, the low-temperature transformations and mineral assemblages were influenced not only by temperature but also by local rock composition, fluid-rock ratio, and fluid chemistry.
Description
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Citation
Clays and Clay Minerals, Vol. 60, No. 1, 1–17, 2012.
Publisher
The Clay Minerals Society
License
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