Abstract

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 δ 18 O and 1 to 3‰ in δ 13 C. 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 δ 18 O and 1 to −5‰ in δ 13 C. 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 δ 18 O and −3 to −4‰ in δ 13 C. 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 δ 18 O and −3 to −12‰ in δ 13 C, and an X CO 2 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 X CO 2 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 X CO 2 less than 0.05, but this is obscured by the production of CO 2 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 δ 18O ≤ 10‰ and δ 13 C of −5 to −7‰.

Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call