Abstract

Repartitioning of rare-earth elements (REE) during the Grenville granulite facies metamorphism of Adirondack anorthosite has produced metamorphic minerals depleted in the heavy REE relative to concentrations predicted by igneous partition coefficients. The heavy- REE depletion is observed in garnet-bearing metamorphosed anorthosites and results from closed-system repartitioning of REE among heavy-REE-rich garnet and other recrystallizing minerals. The resulting heavy-REE-depleted patterns contrast with primary igneous mineral patterns, which conform to predictions from igneous partition coefficients. Whole-rock REE patterns of Adirondack anorthosites are not affected by the local REE rearrangement. Anorthosite REE patterns reflect their primary igneous mineralogy and are independent of any secondary metamorphic minerals formed during the Grenville metamorphic event. Consequently, the REE did not move more than a few centimetres during the granulite facies metamorphism.

You do not currently have access to this article.