Oxygen and hydrogen isotope disequilibria in the Landsverk I pegmatite, Evje, southern Norway: Evidence for anomalous hydrothermal fluids

Oxygen isotope analysis of certain quartz, amazonite feldspar, and epidote from the Landsverk I pegmatite near Evje, southern Norway, indicates extreme local 18O depletion. The ?18O values of massive, milky white breccia-filling quartz are as light as -7.4 ‰. Marked oxygen isotope exchange was found for amazonite, but not for fragments of microcline perthite in the breccia. 18O depletion of this
magnitude is characteristic of meteoric-hydrothermally alte red rocks, and the isotopic composition of the appropriate meteoric water is estimated to have been ?18O = 16.0‰ and ?D= -125‰. However, the ?D values of water in only one fluid inclusion sample provide supportive evidence for the presence of
meteoric water, and no large-scale hydrothermal alteration systems are as yet known for the area. The oxygen and hydrogen isotope compositions of Precambrian (?) meteoric water may not correspond to the Epstein-Craig equation for present-day waters. 18O depletion by CO2 exsolution from a late magmatic fluid provides an alternative explanation.