Publication Type:

Journal Article

Authors:

Piilonen, Paula C.; McDonald, Andrew M.; Lalonde, Andre E.

Source:

The Canadian MineralogistThe Canadian Mineralogist, Mineralogical Association of Canada, Ottawa, ON, Canada, Volume 36, Part 3, p.779-791 (1998)

ISBN:

0008-4476

Keywords:

aegirine, augite, Canada, chain silicates, chemical composition, Clinopyroxene, crystal chemistry, crystal fractionation, crystal zoning, crystallization, crystals, eastern canada, enrichment, metals, Mont-Saint-Hilaire Quebec, Mossbauer spectra, peralkalic composition, pyroxene group, quebec, rare earths, Rouville County Quebec, silicates, spectra

Abstract:

In the peralkaline East Hill suite at Mont Saint-Hilaire, clinopyroxenes range from aegirine-augite (Ae (sub 38) Di (sub 39) Hd (sub 23) ) to end-member aegirine (Ae (sub 97) Di (sub 1.5) Hd (sub 1.5) ). All samples show complex chemical and optical zonations; cores are greatly enriched in Ca + Zr, whereas rims are enriched in Na + Ti. Moessbauer, Fe titrations and structural formulae all indicate that > 85% of the total Fe is present as Fe (super 3+) and is presumably restricted to the M1 site. The aegirine in this suite is enriched in REE relative to chondrite, and shows a strong, negative Eu anomaly; two patterns are noted, one concave with enrichments in both HREE and LREE, and the other (in aegirine with a fibrous habit) with a steep negative slope, enriched in LREE. Fractionation trends lie along the Di-Ae tieline as a result of low Fe (super 2+) /Fe (super 3+) values, unlike those observed in geochemically similar intrusions. Aegirine at Mont Saint-Hilaire is the result of fractionated, late-stage, volatile-rich melts enriched in Na,Fe (super 3+) , and incompatible elements such as Zr, Ti and the REE. An evolutionary scheme is discussed.

Notes:

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