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Grain boundary migration of water and carbon dioxide during uplift of garnet‐zone Alpine Schist, New Zealand
Author(s) -
CRAW D.,
NORRIS R. J.
Publication year - 1993
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/j.1525-1314.1993.tb00154.x
Subject(s) - quartz , geology , schist , fluid inclusions , metamorphic rock , shear zone , inclusion (mineral) , geochemistry , meteoric water , grain boundary , wetting , mineralogy , groundwater , materials science , composite material , geotechnical engineering , paleontology , microstructure , tectonics
Deformed quartz veins in garnet‐zone schist adjacent to the active Alpine Fault, New Zealand, have fluid inclusions trapped along quartz grain boundaries. Textures suggest that the inclusions formed in their present shapes during annealing of the deformed veins. Many of the inclusions are empty, but some contain carbon dioxide with densities that range from 0.16 to 0.80 g cm −3 . No water, nitrogen or methane was detected. The inclusions are considerably more CO 2 ‐rich than either the primary metamorphic fluid (<5% CO 2 ) or fluids trapped in fracture‐related situations in the same, or related, rocks (<50% CO 2 ). Enrichment of CO 2 is inferred to have resulted from selective migration (wicking) of saline water from the inclusions along water‐wet grain boundaries after cooling‐induced immiscibility of a water‐CO 2 mixture. Inclusion volumes changed after loss of water. Non‐wetting CO 2 remained trapped in the inclusions until further percolation progressively removed CO 2 in solution. This mechanism of fluid migration dominated in ductile quartz‐rich rocks near, but below, the brittle‐ductile transition. At deeper levels, hydraulic fracturing is also an important mechanism for fluid migration, whereas at shallower levels advection through open fractures dominates the fluid flow regime.