Metamorphic Patterns of Aluminous Rocks from High and Mid-pressure Crustal Segments of the Central Grenville Province- a Review
Aphrodite Daphnee Indares, Memorial University of Newfoundland, Earth Sciences, St John's, NL, Canada and Greg Dunning, Memorial University of Newfoundland, Earth Sciences, St John's, NF, Canada
Contact First Author: Aphrodite Daphnee Indares; aindares@mun.ca
Previously Published Material: This is a review paper that summarizes work done ande published between 2005 and 1014
English Abstract:
Anatectic aluminous rocks in the Manicouagan area (central Grenville province) provide a record of partial melting, P–T evolution and the timing of metamorphism in granulite-facies crustal segments that were metamorphosed at different times and/or different depths during the Grenvillian orogeny: the southern part of the Parautochthonous belt (SPB), and the high-P and mid-P portions of the hinterland (HPH and MPH respectively).In all segments the aluminous rocks consist of the assemblage garnet , ± biotite ± plagioclase, K-feldspar, and kyanite (in the HPH and in most of the SPB) or sillimanite (in the MPH), with textures suggestive of anatexis by breakdown of micas. The preservation of peak assemblages is consistent with melt migration, but widespread textural evidence of former melt at the sample scale suggests that a melt fraction was retained in most rocks at all levels. Textures and mineral chemistry, in conjunction with phase equilbria modeling, suggest that the rocks in the different segments followed contrasting P–T paths, with: (a) steep dP/dT gradients in the kyanite stability field, up to ~16 kbar and 850–900oC in the HPH; (b) moderate dP/dT gradients limited between the ky-sil transition and the crd-in boundary with a peak at 9–11 kbar and 820–860oC in the MPH; and (c) moderate dP/dT gradients in the kyanite field with a peak at 12–14 kbar and 800–850oC in the SPB. In both the HPH and the SPB, the anatectic melt crystallized in the kyanite field. Monazite U-Pb data indicate that the granulite-facies metamorphism occurred during the Ottawan phase of the Grenvillian orogeny in the HPH (1.05–1.03 Ga) and the MPH (1.08–1.05 Ga; down to 1.02 Ga), and during the Rigolet phase (0.98–0.97 Ga) in the SPB. In addition, ages of 1.0–0. 98 Ga were also recorded by a texturally distinct generation of monazite rims in the SPB, and these ages are coeval with widespread ultrapotassic magmatism in the same crustal segment.
