Figure 7.
Ranges in carbon isotopic compositions of CH4 from whole-rock samples in this study, Zambales gas seeps, mid-ocean ridge (MOR) vent fluids and Southwest Indian Ridge (SWIR) gabbros. δ13CCH4 values in mafic and ultramafic rocks from Cayman encompass the δ13C value of dissolved CH4 in Von Damm endmember fluids (−15.4‰), suggesting that CH4 budgets at Von Damm may be influenced by interaction with olivine-rich rocks in the subsurface. δ13C values of CH4 issuing from Zambales gas seeps at Los Fuegos Eternos (−7.0 ± 0.4‰) and Nagsasa (−5.6‰) lie in between the ranges of δ13CCH4 in serpentinized dunite and peridotite from the ophiolite, suggesting that CH4 gas in Zambales may be sourced from these two rock types. See text for discussion. Data are from [13,14,16,17,19,21,22,71–82].