Sulfide and sulfate saturation of dacitic melts as a function of oxygen fugacity

Sulfur is a key element in terrestrial magmatic processes yet its geochemical behavior remains one of the most difficult to model due heterovalent chemistry. The maximum amount sulfur silicate melt can dissolve before saturating with sulfide (e.g., pyrrhotite) or sulfate anhydrite) changes redox state system and has important implications for budget system. Several empirical models have been developed predict content at either (under reducing conditions) oxidizing saturation, but only existed that systematically assessed how basaltic as function oxygen fugacity (fO2) across transition from sulfide- sulfate-dominated conditions. applicability intermediate felsic melts rests on assumption composition do not affect dissolves melt. Here, we report new experimental data constrain concentration saturation (SCSS) anhydrite (SCAS) dacitic fO2. experiments were conducted using H2O-saturated natural 1000 °C, 300 MPa, log fO2 varying over four orders magnitude encompassing sulfide-sulfate (log = ΔFMQ−0.7, ΔFMQ+0, ΔFMQ+0.5, ΔFMQ+1, ΔFMQ+1.48, ΔFMQ+1.54, ΔFMQ+1.75, ΔFMQ+2.08 ΔFMQ+3.3). New SCSS SCAS modeling reveals occurs ΔFMQ+1.81 ± 0.56, defined by following equations evolved fO2: SCSSdacitic [S2−] (1 + 10(2.00ΔFMQ – 3.05)) SCASdacitic [S6+] e(1.26 2.00ΔFMQ))