Microstructural and Geochemical Controls on the Crystallization of Garnet and Staurolite: An Example From the Meguma Terrane, Nova Scotia

Nagurney, Alexandra B.; Caddick, Mark J.

doi:10.1130/abs/2020se-345391

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“…In each case, garnet overgrows a foliation which is defined by the shape preferred orientation of prograde chlorite and muscovite. This persistence of primary chlorite and muscovite is consistent with calculated phase assemblages for the Nelson aureole samples at apparent peak temperatures of ~ 530 °C and 3.5 kbar 24 and for the Mosher's Island formation sample at 550 ºC and 4.1 kbar 27 . Sample 2018PPGrt_01 also contains staurolite and late-stage chlorite overgrowths that are texturally distinct from the primary chlorite (Supplemental Fig.…”

Section: Sample Descriptionsupporting

confidence: 86%

Preferred orientations of garnet porphyroblasts reveal previously cryptic templating during nucleation

Nagurney

Caddick

Pattison

et al. 2021

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Electron back scattered diffraction data of garnet crystals from the Nelson Aureole, British Columbia and the Mosher’s Island formation, Nova Scotia, reveals that 22 garnet crystals are all oriented with one of three crystal directions parallel to the trace of the foliation plane in thin section. Structural models suggest that these relationships are due to preferential garnet nucleation onto muscovite, with the alignment of repeating rows of Al octahedra and Si tetrahedra in each leading to inheritance of garnet orientation from the muscovite. These results highlight that epitaxial nucleation may be a prevalent process by which porphyroblast minerals nucleate during metamorphism and carry implications for the role that non-classic nucleation pathways play in the crystallization of metamorphic minerals, the distribution of porphyroblasts in metamorphic rocks, and, in cases in which nucleation is the rate limiting step for crystallization, the energetics of metamorphic reactions.

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Section: Sample Descriptionsupporting

confidence: 86%