Deep to Shallow Sulfide Saturation at Nisyros Active Volcano.

We report new petrographic and geochemical observations on magmatic sulfides occurring in different enclave types, including hornblende and/or clinopyroxene‐rich cumulates, and in the host lavas, in Nisyros (South Aegean volcanic arc). We discuss our findings in the context of pre‐existing petrological and thermobarometry studies. Our results indicate that sulfides become less abundant and Cu‐richer (Cu median values) with magma differentiation at progressively lower pressure/P‐temperature/T‐depth conditions. Starting with high T‐P sulfide‐free pillow lavas and wehrilitic cumulates still representing a sulfide undersaturated system, passing to high T and lower P, deep‐forming sulfide‐rich and hornblende‐rich gabbroic enclaves (SiO2 = 53–55 wt.%, 4–5 × 10−5 area %, Cu = 260 μg/g) at the base of the crust (∼25–30 km), then to clinopyroxene‐rich gabbroic micro‐cumulates (2–3 × 10−5 area %, Cu = 570 μg/g) forming in shallower crustal levels (∼10 km), then to more evolved sulfide‐poor hybrid enclaves (SiO2 = 56–70 wt.%, 1 × 10−5 area %, Cu = 602 μg/g), and finally to even more sulfide‐poor rhyodacitic host lavas (SiO2 = 66–76 wt.%, <0.5 × 10−5 area %, Cu = 6.4 wt.%) differentiating at even shallower crustal levels (∼7 km). Sulfide‐free quenched basaltic andesitic enclaves differentiating near surface levels, carry no textural evidence of pre‐existing magmatic sulfides suggesting that the system returned to a sulfide‐undersaturated state. Finally, we point out two important processes for sulfide evolution, a reaction replacement of clinopyroxene by amphibole observed in the deep‐forming hornblende‐rich gabbroic enclaves triggering the onset of sulfide saturation, and an increased mafic input followed by magma mingling and enclave disaggregation leading to sulfide dissolution and Cu‐enrichment of the magmas. Plain Language Summary: In this study we investigate the occurrence and chemistry of magmatic sulfide minerals found within volcanic lavas, and within smaller rock inclusions (‐enclaves), of Nisyros active volcano, located in the Aegean arc. Sulfides are the main repositories of Cu and other precious metals and thus determine their availability in the residual ascending melt which in turn affects the potential of a system to produce an economic ore deposit. Meanwhile, enclaves offer a unique possibility to "access" different parts of a plumbing system, as they preserve the information corresponding to a specific depth range. Our results are discussed in the context of previous studies which have extensively studied the plumbing system of Nisyros. Understanding what triggers the formation of these sulfides, as well as how do they evolve from the roots to the surface of a well‐studied plumbing system can help to further constrain metal transport and concentration through the crust. Our results suggest that sulfides: (a) form at the base of the crust with the first occurrence of amphibole, (b) become less abundant and Cu‐richer with magma evolution at progressively lower crustal depths, and (c) dissolve, thus causing the release of metals back in the system. Key Points: Magmatic sulfide saturation is triggered at the base of the crust due to the replacement of clinopyroxene by amphiboleMagmatic sulfide abundance and composition vary according to magma evolution and the T‐P‐depth of magma differentiationIncreased mafic input followed by magma mingling and enclave disaggregation lead to sulfide dissolution and Cu‐enrichment of the magmas [ABSTRACT FROM AUTHOR]