Chalcophile element partitioning between Cu-rich sulfide phases and silicate melt and implications for the formation of Earth's continental crust.

To constrain the behavior of chalcophile (sulfide-loving) elements during arc magmatic differentiation and to understand the formation conditions of Earth's continental crust, the partition coefficients (D) of Mn, Co, Cu, Zn, As, Se, Mo, Ag, Cd, Sn, Sb, Te, Re, Au, Pb, and Bi between monosulfide-solid-solution (MSS), Cu-rich sulfide liquid (SL; containing 11–45 wt.% Cu), and hydrous silicate melt (SM) of basaltic to dacitic compositions were determined at 1000–1200 °C, 0.5–1.0 GPa, and f O 2 1–1.5 log units above the fayalite–magnetite–quartz (FMQ) buffer. The D SL / S M values are 16–160 for Co, 1100–8400 for Cu, 50–220 for Se, 1200–5900 for Ag, 50–1800 for Cd, 700–3300 for Te, 15–510 for Re, 5700–90,000 for Au, 20–440 for Pb, and 140–3300 for Bi. The D SL / S M values for Mn, Zn, As, Mo, Sn, and Sb are below 1–40. The D MSS / S M values are 55–260 for Co, 530–1700 for Cu, 74–110 for Se, 30–110 for Ag, 4–40 for Cd, 15–70 for Te, 200–5900 for Re, and 140–270 for Au. The D MSS / S M values for Mn, Zn, As, Mo, Sn, Sb, Pb, and Bi are below 1–3. The D SL / S M of Au increase with increasing Cu content of the sulfide liquid, but the D SL / S M of the other elements little affected by the Cu concentration in the sulfide liquid. Because of their distinct dissolution mechanisms in the silicate melt, the D SL / S M and D MSS / S M of Mn, Co, Zn, Cd, Sn, and Pb are mainly controlled by the silicate melt FeO tot content ([FeO tot); the D SL / S M and D MSS / S M for Re, Mo, As, Sb, and Bi are mainly controlled by [FeO tot and f O 2 ; the D SL / S M and D MSS / S M for Cu, Ag, and Au are mainly controlled by [FeO tot and the content of reduced sulfur in the silicate melt; and the D SL / S M and D MSS / S M for Se and Te are mainly controlled by f O 2. Using all available D SL / S M and D MSS / S M data, a partitioning model was developed for predicting D SL / S M and D MSS / S M of chalcophile elements as a multi-function of temperature, pressure, f O 2 , and silicate melt and sulfide compositions. Sulfide phase relations suggest that the sulfides precipitating from arc magmas containing >100 µg/g Cu in the silicate melt occur as Cu-rich sulfide liquid, whereas the sulfides precipitating from arc magmas containing 30–70 µg/g Cu in the silicate melt occur as mixed MSS and Cu-rich sulfide liquid. Modeling the Cu evolution trends of global arc magmas illustrates that the precipitating sulfides are dominantly MSS in continental arcs with a crustal thickness of >30 km, with the proportion of sulfide liquid being less than 20%; whereas, in island arcs with a crustal thickness of <20 km, the proportion of sulfide liquid may reach up to 90%. Applying the model to predict the evolution trends of Ag, As, Sn, Sb, Se, Mo, Re, Mo, Au, Pb, and Bi in global arc magmas under various f O 2 conditions, we find that when no more than 10% of the precipitating sulfides are sulfide liquid, the chalcophile element patterns of oxidized magmas (0–1 log unit above FMQ) in continental arcs match that of Earth's bulk continental crust, which implies that Earth's continental crust formed mainly in oxidized continental arcs. [ABSTRACT FROM AUTHOR]