O and H isotopic evidence for a mantle source of water in appinite magma: An example from the late Neoproterozoic Greendale Complex, Nova Scotia

Appinite suite rocks occur as small plutonic bodies, ranging from ultramafic to felsic in composition, that are characterized by abundant idiomorphic amphibole suggesting they the products of water-rich mafic magmas. Appinites also understood record tectono-magmatic processes during waning stages subduction convergent collisional tectonic settings. Measuring D/H and 18O/16O ratios hornblende appinitic offers opportunities constrain sources water (mantle, crustal, sea or meteoric) magma its crystallization, shed light on role arc magmatism shuts down. The ca. 607 Ma Greendale Complex Avalon terrane Nova Scotia, Canada, is spectacular exposures appinite composition. Two populations amphiboles identified: one δ18O values between 4.7 6.8‰ anomalously low δD (ca. < −90‰). These isotopic signatures interpreted represent incorporation mantle-derived fluids into crystal structure, possibly associated with mixing a region mantle upwelling subducting slab. This process allows for hydration ascent overlying lithospheric wedge. Some retain mantle-like values, but others may have partially re-equilibrated T assimilation supracrustal units (e.g. organic-rich sediments) derived such bodies. A second generation yields varying 0.9 4.6‰ −106 −64‰, which supports equilibration crustal sources. Assimilation volatiles sourced previously hydrothermally altered intruded sheets country rock produce these second-generation signatures. Regional syntheses indicate ended transform system, implying potential slab window behind system. In context, been emplaced after cessation failure setting asthenospheric generated juvenile magmas and/or facilitated melting continental mantle. Our data support this model together available Sm-Nd data, suggest triggered was hydrated contributed origin appinites.