Decompression-induced crystallization

We are studying the temporal evolution of feldspar crystallization kinetics during isothermal decompression. Rapid decompressions followed by anneal intervals allow evaluation of the kinetics of feldspar crystallization in the groundmass. Growth of pre-existing phenocrysts and newly-formed sparse microlites dominate crystallization at small effective undercoolings, and equilibrium crystal modes are achieved. Microlite nucleation is the dominant transformation process for large effective undercoolings, and chemical equilibrium is not attained under these conditions. Feldspar morphology varies systematically with increasing DT_eff (decreasing final pressure), from euhedral planar faceted to hopper, swallowtail, and dendritic habits.

Hammer, J.E., and M.J. Rutherford, An experimental study of the kinetics of decompression-induced crystallization in silicic melt, Journal of Geophysical Research B: Solid Earth, 107 (1), 8-1 - 8-24, 2002.

Hammer, JE (2004) Crystallization in Hydrous Magmas. Penrose Conference on Neogene-Quaternary Continental Margin Volcanism. Metepec, MX

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