Stable isotope evidence for a massive hydrothermal system related to the Coryell Intrusive Suite, British Columbia

Stable isotopic analysis of thirty-five samples from the alkaline Coryell Intrusive Suite (CIS) indicate that huge meteoric-hydrothermal systems affected these plutons during emplacement into the shallow crust near the end of Eocene extension in southeastern British Columbia. Significant lowering of delta 18O and deltaD values and 18O/16O disequilibrium among mineral assemblages from the Arrow Lake, Renata, and Coryell plutons indicate that hydrothermal activity was intense and was active over a ∼300,000 year duration. The absence of geographic trends in delta 18O and deltaD values indicates that this hydrothermal system was pervasive over a large area (∼3500 km2). Quartz delta 18O values suggest a lower crustal source for the CIS magmas. Melting was triggered by decompression of the lower crust, as it was unroofed during Eocene extension. The overlapping of amphibole and biotite delta 18O values from the CIS and Penticton Group Volcanics suggest a cogenetic relationship between these two units.