Sulfur isotope behavior during metamorphism and anatexis of Archean sedimentary rocks: A case study from the Ghost Lake batholith, Ontario, Canada

Coupling sulfur and oxygen isotope ratios in sediment melts across the Archean-Proterozoic transition

“…through assimilation and partial melting of sediments) formed under the anoxic pre-GOE atmosphere. The transfer of sulfur isotope signatures from sediments into the igneous rock record has been documented in previous studies (Bekker et al, 2009;LaFlamme et al, 2018a;Bucholz et al, 2020). A previous study on an Archean sedimentderived granitic batholith and its source rocks demonstrated that during the process of metamorphism and partial melting, d 34 S values are fractionated from the sedimentary protolith values by at most +2‰ to +3‰ and that S-MIF values are preserved (Bucholz et al, 2020).…”

“…This absence of strongly fractionated sulfides in pre-GOE sediments has been linked to low seawater sulfate concentration resulting in small S isotope fractionation during microbial sulfate reduction (Canfield, 2001). Alternatively, the low d 34 S value in this sample could arise during fractionation between S 2in the melt and H 2 S in a vapor phase (produced through metamorphic devolatilization) as documented for other samples from the Superior Craton (Bucholz et al, 2020). Note that at the low oxygen fugacities recorded by some pre-GOE sediment-derived granitoids (Bucholz et al, 2018) H 2 S (as opposed to SO 2 ) is the dominant sulfur-bearing vapor phase (Poulson and Ohmoto, 1989).…”

“…The transfer of sulfur isotope signatures from sediments into the igneous rock record has been documented in previous studies (Bekker et al, 2009;LaFlamme et al, 2018a;Bucholz et al, 2020). A previous study on an Archean sedimentderived granitic batholith and its source rocks demonstrated that during the process of metamorphism and partial melting, d 34 S values are fractionated from the sedimentary protolith values by at most +2‰ to +3‰ and that S-MIF values are preserved (Bucholz et al, 2020). This gives us confidence that we can interpret the S isotope signature of our samples in the context of the bulk sedimentary packages from which they were derived.…”

“…In addition, enhanced oxidative weathering of sulfides and the formation of oceanic sulfates facilitated the production of highly fractionated sulfides by sulfur-metabolizing bacteria supporting the generation of S-MDF signatures (Guo et al, 2009). Recent studies show that fluctuations in atmospheric oxygen levels are also captured in the igneous rock record; namely, through transport of S-MIF into the crust (Bekker et al, 2009;LaFlamme et al, 2018a;Bucholz et al, 2020), and a change in oxygen fugacity of strongly peraluminous granites (Bucholz et al, 2018).…”

“…granitoids that partially or wholly derived from the partial melting of metasediments). The oxygen and sulfur isotope ratios in sediment-derived granitoids are strongly influenced by the isotopic composition of their sedimentary source rocks (Bindeman, 2020;Bucholz et al, 2020). Hence, sedimentderived granitoids provide a high-fidelity record of these isotopic signatures in bulk siliciclastic sediments that can be tied to magmatic crystallization ages.…”