A Mélange of Subduction Ages: Constraints on the Timescale of Shear Zone Development and Underplating at the Subduction Interface, Catalina Schist (CA, USA)

The presence of mélange at the subduction interface influences numerous geochemical and geophysical processes. However, relationship between timescales development, deformation, resultant mass transport is poorly understood. Here, we use Sm-Nd garnet geochronology to elucidate timing peak metamorphism for five amphibolite tectonic blocks from amphibolite-facies zone Catalina Schist (Santa Island, CA). Ages range 108 116 Ma do not appear correlate with metamorphic temperature recorded by each block (between 640 740°C). lack correlation age favors mixing model previously proposed unit. These ages overlap previous estimates 111–114 but are predominately younger than an estimate structurally lower coherent unit ca. 115 Ma. White mica 40Ar/39Ar studies suggest that units cooled asynchronously 400–425°C 106 97 rates 18 43°C/Ma. Collectively, these results demonstrate formation occurred over least 8 Myr was followed cooling. structural chronologic underlying lower-grade indicates cooling in conjunction underplating event 109 discrepancy may indicate two were juxtaposed either during or after event.