Recognition and Significance of Multiple Fluid Inclusion Generations in Telogenetic Calcites

Philippe Muchez1 and Marek Slobodnik1, 2
1 Fysico-chemische geologie, K.U.Leuven, Celestijnenlaan 200C, B-3001 Leuven, Belgium
2 Department of Geology and Paleontology, Masaryk University, Kotlarska 2, 61137 Brno, Czech Republic

Abstract: Ferroan and non-ferroan calcites occur in fractures in the Lower Carboniferous of the Variscan foreland of southern Belgium. These fractures post-date the Variscan orogeny and the calcites have a telogenetic origin. The non-ferroan calcites formed by recrystallization of the ferroan calcites. Two types of monophase aqueous fluid inclusions are present in the ferroan calcite cement. Although both types of inclusions formed at a temperature not exceeding 50°C, one type contains a moderately saline fluid (3.6–16.3 eq. wt.% NaCl) and the other type fresh water (Tm ice = 0°C The fluid inclusions in the non-ferroan calcite also contain flesh water.

Detailed petrography of the fluid inclusions indicate that the flesh water migrated through the crystals along opened cleavage planes and microfractures. Therefore, they have a secondary origin. The recrystallization of the ferroan calcites to non-ferroan calcites occurred in this fresh water. The saline fluid inclusions are not related to the above mentioned microstructures and although their origin remains unknown, they could represent the ambient fluid from which the ferroan calcites precipitated. The study of the relationship between the occurrence of fluid inclusions and the microstructures seems promising for the identification of fluid inclusions representing post mineral formation fluid and temperature conditions in calcite cements.

Keywords: telogenetic calcites • fluid inclusions • fresh water • cleavage planes • microfractures

Mineralogical Magazine; October 1996 v. 60; no. 402; p. 813-819; DOI: 10.1180/minmag.1996.060.402.12
© 1996, The Mineralogical Society
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