Nadeau, Olivier; Stevenson, Ross et Jébrak, Michel
(2016).
« Evolution of Montviel alkaline–carbonatite complex by coupled
fractional crystallization, fluid mixing and metasomatism — part I:
Petrography and geochemistry of metasomatic aegirine–augite and biotite: Implications for REE–Nb mineralization ».
Ore Geology Reviews, 72, pp. 1143-1162.
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Résumé
Magmatic volatiles are critically important in the petrogenesis of igneous rocks but their inherent transience hampers the identification of their role in magmatic and mineralization processes. We present evidence that magmatic volatiles played a critical role in the formation of the 1894 Ma Paleoproterozoic Montviel alkaline–carbonatite complex, Canada, and the related carbonatite-hosted REE–Nb deposit. Field and drill core relationships indicate that lithological units of the complex were emplaced in the following order: clinopyroxenites, melteigites, ijolites, melanosyenites, leucosyenites, granites, lamprophyric silicocarbonatites, rare magnesiocarbonatites, calciocarbonatites, ferrocarbonatites, late mixed carbonatites, kimberlitic silicocarbonatites and polygenic breccias.
...
The results presented herein suggest that the mantle magmas evolved through 4 distinct mantle pulses by fractional crystallization, mixing of depleted mantle fluids with crustal fluids, and metasomatism. Some of the silicate rocks also show evidence of assimilation of wall rock as part of their petrogenetic evolution. During the last stages of its evolution in carbonatites, the fluid source transited from the depleted mantle to the crust and we speculate that this resulted in a violent explosive eruption creating the diatreme-shaped, HREE-rich polygenic breccia.
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