A MINERALOGICAL AND GEOCHEMICAL INVESTIGATION OF THE INFLUENCE OF TECTONIC SETTING ON SULFUR CYCLING DURING SERPENTINIZATION ALONG THE WESTERN NORTH AMERICA MARGIN

Serpentinites are metamorphic rocks typically produced by hydration of mantle peridotites to form assemblages containing one or more serpentine minerals. They occur in a variety of tectonic and geologic settings, e.g., submarine hydrothermal systems, ophiolite sequences, and the forearc mantle. Because accessory sulfide minerals are commonly found within serpentinites, and because serpentine minerals themselves can also contain structurally bound sulfur, serpentinization likely plays a role in sulfur cycling in the lithosphere. Previous investigations of sulfur geochemistry have focused on abyssal oceanic serpentinites, e.g., along the Mid-Atlantic ridge system. However, no study has been conducted to investigate whether and how sulfur geochemistry varies between serpentinites from different tectonic settings. To address this, we collected serpentinites from the wide variety of tectonic settings available in Western North America, including the New Idria forearc diapir, Canyon Mountain island arc complex, Josephine ophiolite, and the Franciscan accretionary prism complex. We present initial petrographic, geochemical, and bulk stable isotopic analyses of serpentinites from each of these settings. Our results may permit the development of petrological and geochemical markers for constraining the tectonic origins of serpentinites in the rock record. Constraints provided by analyses of forearc serpentinites may increase our understanding of the fate of sulfur in subduction zones.