TY - JOUR
T1 - Isotopic and petrological evidence for the infiltration of water-rich fluids during the Miocene M2 metamorphism on Naxos, Greece
AU - Baker, Judy
AU - Bickle, M. J.
AU - Buick, I. S.
AU - Holland, T. J.B.
AU - Matthews, A.
PY - 1989/8
Y1 - 1989/8
N2 - A detailed carbon and oxygen isotopic study, in conjunction with petrological work, has been carried out across calcite-dolomite marble layers in the high-grade metamorphic sequence on the island of Naxos, Greece. The purpose of this study is to examine fluid flow during the Miocene Barrovian metamorphic event. Individual marble bands show two dominant styles of isotopic alteration from core values of 22 to 29‰ in δ18O and 1 to 3‰ in δ13C. Firstly, contacts between the marble bands and surrounding pelitic rocks have altered isotopic ratios across a metre wide boundary layer. The isotopic values of the marble along the contacts drop to 15 to 17‰ in δ18O and 1 to -5‰ in δ13C. Secondly, there is a drop in the isotopic composition of the marbles along vein networks associated with the development of calc-silicates. The isotopic compositions in these veins drop to 14 to 16‰ in δ18O and -3 to -4‰ in δ13C. Cross-cutting relationships observed between these two alterations allow the relative timing of infiltration to be determined. The development of boundary layers is shown to result from the infiltration of fluids with isotopic signatures of 12 to 16‰ in δ18O and -3 to -12‰ in δ13C, and an XCO2 less than 0.3. These fluids are derived from dehydration of graphite-bearing pelites during the prograde metamorphism. These conclusions are at odds with those of previous workers who suggested that the prograde metamorphism was a result of the pervasive influx of mantle-derived fluids with XCO2 greater than 0.5. The alteration associated with vein networks results from peak to post-peak infiltration of fluids which drive decarbonation reactions. At least some of these fluids have an XCO2 less than 0.05, but this is obscured by the production of CO2 during the decarbonation reactions. These fluids were most probably produced from the crystallising partial melts formed during the prograde metamorphism. These infiltrating fluids are thought to have δ18O ≤ 10‰ and δ13C of -5 to -7‰.
AB - A detailed carbon and oxygen isotopic study, in conjunction with petrological work, has been carried out across calcite-dolomite marble layers in the high-grade metamorphic sequence on the island of Naxos, Greece. The purpose of this study is to examine fluid flow during the Miocene Barrovian metamorphic event. Individual marble bands show two dominant styles of isotopic alteration from core values of 22 to 29‰ in δ18O and 1 to 3‰ in δ13C. Firstly, contacts between the marble bands and surrounding pelitic rocks have altered isotopic ratios across a metre wide boundary layer. The isotopic values of the marble along the contacts drop to 15 to 17‰ in δ18O and 1 to -5‰ in δ13C. Secondly, there is a drop in the isotopic composition of the marbles along vein networks associated with the development of calc-silicates. The isotopic compositions in these veins drop to 14 to 16‰ in δ18O and -3 to -4‰ in δ13C. Cross-cutting relationships observed between these two alterations allow the relative timing of infiltration to be determined. The development of boundary layers is shown to result from the infiltration of fluids with isotopic signatures of 12 to 16‰ in δ18O and -3 to -12‰ in δ13C, and an XCO2 less than 0.3. These fluids are derived from dehydration of graphite-bearing pelites during the prograde metamorphism. These conclusions are at odds with those of previous workers who suggested that the prograde metamorphism was a result of the pervasive influx of mantle-derived fluids with XCO2 greater than 0.5. The alteration associated with vein networks results from peak to post-peak infiltration of fluids which drive decarbonation reactions. At least some of these fluids have an XCO2 less than 0.05, but this is obscured by the production of CO2 during the decarbonation reactions. These fluids were most probably produced from the crystallising partial melts formed during the prograde metamorphism. These infiltrating fluids are thought to have δ18O ≤ 10‰ and δ13C of -5 to -7‰.
UR - http://www.scopus.com/inward/record.url?scp=0024873358&partnerID=8YFLogxK
U2 - 10.1016/0016-7037(89)90323-2
DO - 10.1016/0016-7037(89)90323-2
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AN - SCOPUS:0024873358
SN - 0016-7037
VL - 53
SP - 2037
EP - 2050
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
IS - 8
ER -