CONSONORM_HG: a new method of norm calculation for mid- to high-grade metamorphic rocks

French Title: CONSONORM_HG : une nouvelle méthode de calcul normatif pour les roches métamorphiques de grades intermédiaires à élevés

Lucie Mathieu, CONSOREM (Consortium de Recherche en Exploration Minérale - mineral exploration research consortium), Département des sciences appliquées, UQAC, Chicoutimi, QC, Canada, Sylvain Trépanier, Mines Virginia, 300 Saint-Paul, suite 200, Québec, QC, Canada and Réal Daigneault, Centre d'études sur les Ressources minérales (CERM), Département des sciences appliquées, UQAC, Chicoutimi, QC, Canada

Contact First Author: Lucie Mathieu; mathiel@tcd.ie

Abstract ID#: 34262

 

English Abstract:
The CONSONORM_HG norm provides a standardised solution to approximate metamorphic parageneses for mid- to high-grade metamorphic rocks. This norm integrates ternary phase diagrams computed using the Perple_X software developed by J. Connolly and collaborators (cf. http://www.perplex.ethz.ch/). What the CONSONORM_HG losses in precision, when compared to pseudo-sections and other types of diagrams abundantly used by metamorphic petrologists, it gains in simplicity and universality, as the CONSONORM_HG can be applied to any type of metamorphic rocks, whether their protoliths have the mafic or felsic composition of sedimentary, magmatic or hydrothermally altered rocks.

The CONSONORM_HG is designed for silicate, Fe-Ti oxydes and/or carbonate-dominated rocks, and it approximates the main parageneses of metamorphic rocks for pressures < 10 kbars and for the greenschist, blueschit, amphibolite and granulite facies. For each of the 17 P-T conditions modelled and depending on the Fe-Mg-Mn composition of the sample, the norm calculates silicate assemblages using one among three Al-Ca-NaK-FeMgMn tetrahedrons that are a convenient way to represent a large amount of silicate assemblages. In addition to silicates, the CONSONORM_HG calculates accessory minerals, Fe-Ti oxides, sulphides from analysed sulfur and/or from analysed metals and carbonates from analysed CO2 or from normative CO2 estimated from the LOI, following the NORMAT method. The CONSONORM_HG also integrates many reactions to address silicon deficits, as well as quartz-carbonates reactions, to better approximate natural parageneses.

The CONSONORM_HG was initially intended to facilitate the recognition of hydrothermally altered rocks in high-grade metamorphic area. This tool has also the potential to serve for the classification of metamorphic rocks, as the CIPW norm served the classification of magmatic rocks. This presentation will focus on the calculation sequence of the CONSONORM_HG.

Back to: Using Computational Thermodynamics to Model Natural Systems: Recent Advances and Challenges for the Future I