Abstract

Microthermometric measurements of partial or total homogenization to the vapor phase (via liquid disappearance) in fluid inclusions yield erroneously low temperatures resulting from the inability to detect small amounts of liquid remaining in the inclusion at the apparent homogenization point. This "apparent homogenization phenomenon" is quantitatively addressed using specific numerical examples based on published synthetic fluid inclusion data. Synthetic inclusions allow the accurate characterization of the true homogenization temperature, and thus, permit quantification of the error in the observed T h l + v(v) measurements.Apparent total homogenization to the vapor phase has been observed in NaCl-H 2 O and CO 2 -H 2 O inclusions at as much as [asymp]500 degrees and [asymp]25 degrees C, respectively, below the true homogenization temperatures, whereas apparent partial homogenization of CO 2 to the vapor phase has been observed in CO 2 -H 2 O inclusions down to [asymp]4 degrees C below true T (sub h (sub CO 2 ) ) . These observations have been recorded in inclusions with shapes that should facilitate the observation of even small amounts of a liquid phase.In some cases the volume of liquid remaining in the inclusion at the temperature of apparent homogenization was also determined. In CO 2 -H 2 O inclusions, as much as [asymp]25 vol percent CO 2 liquid (relative to CO 2 liquid + CO 2 vapor) may be concealed in inclusions that appear to contain only CO 2 vapor and aqueous liquid. Similar amounts of liquid may also be present in NaCl-H 2 O and CO 2 -H 2 O inclusions that appear to have homogenized totally and contain only vapor.Considerable uncertainty is introduced into the calculation of geochemical parameters when these calculations are based on T h l + v(v) measurements--particularly those recorded on inclusions having near-critical densities. Specific examples of errors in geothermometry, geobarometry, and determinations of bulk fluid compositions based on T (sub h (sub CO 2 ) ) measurements from CO 2 -H 2 O inclusions are discussed.

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