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The duration of near‐peak metamorphism from diffusion modelling of garnet zoning
Author(s) -
Spear F. S.
Publication year - 2014
Publication title -
journal of metamorphic geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.639
H-Index - 114
eISSN - 1525-1314
pISSN - 0263-4929
DOI - 10.1111/jmg.12099
Subject(s) - kyanite , geology , chlorite , metamorphic rock , metamorphism , staurolite , diffusion , biotite , geochemistry , mineralogy , closure temperature , isograd , tectonics , quartz , geomorphology , seismology , thermodynamics , paleontology , metamorphic facies , structural basin , physics , facies
Garnet in a staurolite–kyanite zone sample from central Vermont displays a bell‐shaped Mn growth zoning with diffusional modification over the outer 100 μ m. The diffusion is driven by the prograde net transfer reaction garnet + chlorite = kyanite + biotite as is evidenced by a well‐defined resorption zone on the rim. Analysis of the reaction history and resorbed garnet composition suggests that the peak temperature attained was 620–660 °C. Diffusional modelling of the rim diffusion provides an estimate of the duration of the metamorphic episode over which significant garnet diffusion occurs. The duration is a function of the assumed peak temperature and garnet diffusivities and range from a few hundred thousand years to a few million years. Such short durations require rapid tectonic burial and exhumation of relatively thin tectonic slices.