Computer Science
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995e%26psl.134..319f&link_type=abstract
Earth and Planetary Science Letters, vol. 134, Issue 3-4, pp.319-328
Computer Science
1
Scientific paper
Migmatites at Brattstrand Bluffs, East Antarctica, comprise granulite-facies mineral assemblages produced by high-temperature metamorphism of pelitic sediments. These rocks preserve an advanced stage of partial melting, with recrystallized melt accounting for ~ 25% of outcrop area. Many of the melt veins contain cordierite, which traps volatile molecules within open channels in its mineral framework and can be used to monitor the syn-metamorphic volatile contents of the melts. We have analysed the isotopic composition of cordierite channel CO 2 by step-heating mass spectrometry. Channel CO 2 in cordierite from Brattstrand Bluffs has not been significantly affected by retrograde isotope exchange as it preserves high-temperature carbon fractionations with coexisting graphite. Cordierite samples from the same locality have similar isotope compositions (±0.6 ), reflecting efficient mixing of partial melt and dissolved volatiles on a metre scale. However, samples from different localities have distinct 13 C values (-10 to -20 ), and indicate that there was little mixing of melt or volatiles on a scale of ~ 100 m despite the high degree of partial melting. The 10 variation between localities reflects mixing of variable proportions of isotopically light biogenic carbon with carbon from a heavier reservoir. Although this mixing can be interpreted in terms of carbon influx from an external source, CO 2 was not a driving force for granulite metamorphism in this case as granulite assemblages occur at all localities irrespective of isotope systematics. CO 2 played a complex but passive role during metamorphism and melting at Brattstrand Bluffs, where the dissolution of H 2 O into partial melt bodies was the dominant dehydration mechanism.
Fitzsimons C. W. I.
Mattey David P.
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