Deep CO2 and N2 emissions from Peruvian hot springs: Stable isotopic constraints on volatile cycling in a flat-slab subduction zone

Supplemental Material: Roadblocks and speed limits: Mantle-to-surface volatile flux through the lithospheric-scale Denali fault, Alaska

“…The Cext at Soda Springs on the Totschunda fault, is the highest of any in this study (nearly 0.14 molal), and near the upper end observed in the literature (e.g., Chiodini et al, 2000;Crossey et al, 2009;Hiett et al, 2022). The Cext is dominated by an endogenic endmember with a d 13 C value of ~0 ‰, with is consistent with metamorphic decarbonation of marine carbonates.…”

“…Figure S2 shows the relationship between δ 13 Cext values and mCext for the investigated springs. Previous authors employing this method have observed trends explained by binary mixing between a low mCext endmember with low δ 13 Cext value, reflecting small contributions carbon from organic sources, with high mCext endmembers with δ 13 Cext values from marine carbon sources such metamorphic decarbonation or a subducting slab (~0 ‰), mantle (~-6 +/-3 ‰), or other "deep crustal" sources (-14 to -7‰) (Chiodini et al, 2000;Chiodini et al, 2004;Crossey et al, 2009;Hiett et al, 2022). In this study, we compare the calculated δ 13 Cext values and Cext to binary mixing curves between an organic endmember (-30 ‰) and metamorphic decarbonation of marine carbonates (~0 ‰) and a range of mantle (or deep crustal) end members (-6 +/-3‰).…”

“…where x is the mole fraction of H2CO3(aq) and (1-x) is the mole fraction of HCO3 -(aq) determined using PHREEQC (Hiett et al, 2022). The temperature specific ε 13 CH2CO3(aq)-CO2(g) and ε 13 CHCO3(aq)-CO2(g) are calculated using the relationships in Deines et al (1974).…”

Tectonic settings influence the geochemical and microbial diversity of Peru hot springs

“…FSS water stable isotopic values suggest derivation from local meteoric water infiltration with minimal high-temperature water-rock isotopic exchange. In contrast, δ 18 O and δ 2 H values for BAS indicate varying degrees of isotopic exchange at elevated temperatures between infiltrating meteoric water and bedrock and/or mixing with deep geofluids 30 . In both regions, the helium isotope ( 3 He/ 4 He) ratios and the δ 13 C values of dissolved CO 2 derive from a mixture of mantle and crustal sources 29,30 .…”

“…In contrast, δ 18 O and δ 2 H values for BAS indicate varying degrees of isotopic exchange at elevated temperatures between infiltrating meteoric water and bedrock and/or mixing with deep geofluids 30 . In both regions, the helium isotope ( 3 He/ 4 He) ratios and the δ 13 C values of dissolved CO 2 derive from a mixture of mantle and crustal sources 29,30 . BAS geochemistry requires a higher flux of mantlederived volatiles than the FSS, attributed to the presence of an asthenosphere directly below the continental lithosphere and associated higher heat flow.…”