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Late Archaean/Early Proterozoic CO 2 streaming through the lower crust and geochemical segregation
Author(s) -
Newton R. C.
Publication year - 1987
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl014i003p00287
Subject(s) - geology , geochemistry , metamorphism , crustal recycling , proterozoic , archean , gneiss , lile , continental crust , granulite , petrology , craton , crust , partial melting , tectonics , metamorphic rock , paleontology , facies , structural basin
Considerable evidence exists for large‐scale migration of CO 2 ‐rich fluids through the lower continental crust in the Late Archaean and Early Proterozoic, with transfer of heat producing elements and H 2 O to higher levels. The evidence manifest in the large charnockitic terrains of this age includes deformation‐related charnockitic alteration of gneisses, nearly ubiquitous CO 2 ‐rich fluid inclusions in minerals, depletion of large‐ion‐lithophile elements (LILE), particularly Rb, relative to typical upper crustal rocks, similar depletion of 18 O in paragneisses and petrographic and geochemical evidence of open‐system replacement of amphibole gneiss by charnockite. A conveyor‐belt upper mantle source appears to have been necessary for prolonged CO 2 supply in high‐grade crustal metamorphism, most plausibly by deep subduction of marine carbonate under continental interiors. This plate tectonic mode seems consonant with crustal thickening and orogenic patterns inferred for most charnockitic terrains and with CO 2 transport mechanisms constrained by experimental petrology.