We use triple oxygen isotopes of altered granitic rocks to determine the isotope composition of meteoric waters in a fossil hydrothermal system, the low δ18O Eocene Idaho Batholith, originally studied by Criss and Taylor (1983). In doing so we: 1) test whether meteoric water values estimated from previous δ18O and δD analyses on quartz, feldspar and biotite are robust and 2) determine the palaeoelevation of the Eocene highlands that are presently constrained primarily by the δ18O and δD of paired muscovite and quartz from core complexes and altered granites. Our calculated δ18O values of meteoric water are higher than estimates that use combined feldspar δ18O and biotite δD measurements in these hydrothermally altered granites and δD values from muscovite from nearby core complexes (Mulch et al., 2004). Both methods are consistent with a high elevation (∼3.1 to 4.7 km) Eocene highland in the northwestern U.S. Cordillera.
All Science Journal Classification (ASJC) codes
- Environmental Chemistry
- Geochemistry and Petrology