Oxygen fugacity range of subducting crust inferred from fractionation of trace elements during fluid-present slab melting in the presence of anhydrite versus sulfide

Subducted slabs, which include altered-oceanic crust and overlying sediments, impart geochemical redox fingerprints to arc magmas affect long-term evolution of the deep mantle. Yet, oxygen fugacity subducting slab remains poorly constrained. Light Rare Earth Element (LREE) chalcophile element (ChE) ratios may serve as proxies for downgoing slabs because difference in compatibility these groups elements between sulfide (e.g., pyrrhotite: Po) sulfate anhydrite: Anh) whose presence crustal lithologies depend on slab. However, evaluating LREE/ChE magma require a complete understanding partitioning residual phases derived partial melts or fluids. Although previous studies have explored trace silicate melts, similar data are not available anhydrite-melt systems at conditions fluid-present melting. Here we performed laboratory experiments 2 GPa 900–1000 °C investigate 26 lithophile anhydrite hydrous silicic melt. Phases were analyzed using EPMA LA-ICPMS. Sr, Y, Ba, REEs found be compatible while other behave oppositely. Since Ce is Mo Cu not, can use Ce/Cu Ce/Mo near-primary try fingerprint processes involved modifying sub-arc mantle by reduced oxidized melt components. The bulk D (D¯) Ce, Cu, calculated mineralogical modes from melting carried out sediments Altered-Oceanic Crust (AOC). differences D¯Ce/D¯Mo D¯Ce/D¯Cu values anhydrite-saturated sulfide-saturated indicate preferential sediment whereas partitioned into melts. Arc localities featuring signature like Marianas, L. Antilles, Kurile, Cascades, Mexico show that attributed mixing depleted mantle-derived some arcs Cascades), lavas Marianas most needs Our experimental resulting modeling, therefore, suggest crusts likely variable one subduction zone another.