Fluid inclusions in cavity quartz crystals in rapakivi from Luumäki, southeastern Finland

POUTIAINEN, MATTI, 1991. Fluid inclusions in cavity quartz crystals in rapakivi from Luumäki, southeastern Finland. Bull. Geol. Soc. Finland 63, Part 2, 87—93. Fluid inclusions in selected cavity quartz crystals in rapakivi granite from Luumäki, southeastern Finland, were studied by microthermometric methods. Two different compositional types of fluid inclusions were identified: (I) lowto intermediate-salinity mixed H 2 0-C0 2 inclusions (1.8—5.9 eq.wt.% NaCl) and (II) intermediate-salinity aqueous inclusions (3.6—5.2 eq.wt.% NaCl). The different fluid inclusion types occur in different stages of the host crystal growth allowing their paragenetic classification as primary, pseudosecondary and secondary. The temperatures of total homogenization of Type I primary, pseudosecondary and secondary inclusions range from 343 to 372°C, 221 to 236°C and from 160 to 174°C, respectively. The pseudosecondary inclusions of Type II composition show filling temperatures of 214 to 251°C.