TY - JOUR
T1 - Oxygen-isotope geochemistry of the Scourian complex, northwest Scotland
AU - Cartwright, I.
AU - Valley, J. W.
PY - 1992/12/1
Y1 - 1992/12/1
N2 - The Scourian complex of northwest Scotland underwent granulite-facies metamorphism at 2.7 Ga. Granulite-facies orthogneisses have whole-rock δ18O values similar to those of igneous rocks of comparable compositions (ultrabasic gneisses 5.5-5.9‰, basic gneisses 6.4-6.8‰, tonalitic gneisses 9.5-9.7‰), and steep 180 gradients of up to 3‰ in 10cm are recorded at two lithological contacts. These data suggest that large volumes of pervasive metamorphic fluids have not infiltrated the rocks, but do not preclude localized fluid-rock interaction. Scourian paragneisses have lower δ18O values (8.5-9.9‰) than typical metasediments, and may have undergone fluid-hosted isotopic exchange with the surrounding orthogneisses. Felsic sheets within tonalitic and basic gneisses have simillar δ18O values to their hosts: these data, combined with petrological and geochemical information, suggest that the sheets were formed by local anatexis during granulite-facies metamorphism. Fluid infiltration during the 2.5 Ga amphibolitefacies Inverian retrogression caused homogenization of δ18O values of the Scourian gneisses. Unaltered tholeiitic Scourie dykes have low δ18O values of 2.0‰. It is unlikely that heated, surface-derived fluids infiltrated the Scourian complex, and these dykes were probably emplaced as low-δ18O magmas.
AB - The Scourian complex of northwest Scotland underwent granulite-facies metamorphism at 2.7 Ga. Granulite-facies orthogneisses have whole-rock δ18O values similar to those of igneous rocks of comparable compositions (ultrabasic gneisses 5.5-5.9‰, basic gneisses 6.4-6.8‰, tonalitic gneisses 9.5-9.7‰), and steep 180 gradients of up to 3‰ in 10cm are recorded at two lithological contacts. These data suggest that large volumes of pervasive metamorphic fluids have not infiltrated the rocks, but do not preclude localized fluid-rock interaction. Scourian paragneisses have lower δ18O values (8.5-9.9‰) than typical metasediments, and may have undergone fluid-hosted isotopic exchange with the surrounding orthogneisses. Felsic sheets within tonalitic and basic gneisses have simillar δ18O values to their hosts: these data, combined with petrological and geochemical information, suggest that the sheets were formed by local anatexis during granulite-facies metamorphism. Fluid infiltration during the 2.5 Ga amphibolitefacies Inverian retrogression caused homogenization of δ18O values of the Scourian gneisses. Unaltered tholeiitic Scourie dykes have low δ18O values of 2.0‰. It is unlikely that heated, surface-derived fluids infiltrated the Scourian complex, and these dykes were probably emplaced as low-δ18O magmas.
UR - http://www.scopus.com/inward/record.url?scp=0001082202&partnerID=8YFLogxK
U2 - 10.1144/gsjgs.149.1.0115
DO - 10.1144/gsjgs.149.1.0115
M3 - Article
AN - SCOPUS:0001082202
SN - 0016-7649
VL - 149
SP - 115
EP - 125
JO - Journal of the Geological Society
JF - Journal of the Geological Society
IS - 1
ER -