Low-^(18)O meteoric-hydrothermal signatures in groundmass and fiamme of fossil fumaroles of the 0.76 Ma Bishop Tuff, California

A 150-m thick δ^(18)O profile of whole-rock (WR) samples from an area of fossil fumaroles in the Bishop tuff at Owens River Gorge shows a low-^(18)O horizon sandwiched between an essentially unwelded upper portion and a densely-welded lower part displaying magmatic ^(18)O/^(16)O (see figure). Shallow-dipping columnar joints (sdcj) are correlative with the low-^(18)O horizon, the base of which is extremely sharp (~3 per mil per meter).