首页|Modeling the chemical heterogeneity of tonalite-trondhjemite-granodiorite intrusive suites
Modeling the chemical heterogeneity of tonalite-trondhjemite-granodiorite intrusive suites
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NSTL
Insights into the source and partial-melting conditions of tonalite-trondhjemite-granodiorite (TTG) and other tonalite-dominated intrusive suites provide essential constraints on die tectonic regimes prevailing before 2.5 Ga. Most petrogenetic interpretations rely on whole-rock chemical data and neglect the role of differentiation on primitive melt composition. Indeed, the processes of mineral separation from residual melt (fractionation) and of mineral sorting in a low-melt-fraction mush are rarely evaluated for tonalite-dominated magmatism. Here, numerical modeling provides quantitative constraints on fractional crystallization and mineral sorting for tonalite-dominated suites of the Abitibi greenstone belt, Superior craton, Canada. It is concluded that differentiation can be responsible for most within-suite chemical heterogeneity. The modeling shows that amphibole fractionation alone is sufficient to explain the range of HREE observed in the studied intrusive suites, indicating that the relationship between HREE content and partial-melting depth is not always straightforward. The modeling also shows that mineral sorting can explain chemical heterogeneities as well as primitive melts produced at distinct pressures. Also, the fractional crystallization of amphibole under various temperature conditions explains the contrasting Nb and Ti contents of the studied intrusive phases. The chemical heterogeneity of TTG suites can be explained using different modeling assumptions (e.g., fractional crystallization, mineral sorting, melts produced at distinct pressures) and Neoarchean tonalite-dominated magmatism likely results from a diversity of petrogenetic processes. The petrogenesis of individual intrusions should thus be interpreted with caution before drawing conclusions on source processes and, by extension, the geodynamic settings.
CERM (Centre d'Etude des Ressources Minerales), DSA (Departement des Sciences Appliquees), VQAC (Universite du Quebec a Chicoutimi), 555 boul de VUniversite, Chicoutimi G7H 2B1, Canada
NSTL
