Isochoric phase diagrams in the systems CO 2CH 4 and CO 2N 2: Application to fluid inclusions

Abstract

The phase behaviour between −180 and +35°C at constant volume in CO 2CH 4N 2 inclusions includes some newly described phase transitions. All transitions can be [classified] ^ initial or final melting, homogenization, partial homogenization, sublimation or metastable homogenization. Phase sequences are classified in 9 groups, distinguished by the order and number of phase transitions. The variety of phase behaviour is explained by differences in fluid composition and molar volume. Phase assemblages are illustrated by isochoric (constant volume) phase diagrams of the binary systems CO 2CH 4 and CO 2N 2, covering the full range of compositions and molar volumes of interest for natural fluid inclusions. The topologies of V̄TX diagrams for the two binary systems are different and explain the unique phase behaviour of both systems, which can often be distinguished by their phase behaviour only. Both isochoric TX and isothermal V ̄ X sections are discussed. The diagrams allow the determination of molar volumes from microthermometric data and Raman analysis. Phase diagrams for the ternary system CO 2CH 4N 2 could only semi-quantitatively be established.