EXPLORING THE PETROCHRONOLOGY OF SUBDUCTION-RELATED MAGMATISM IN THE ROSS OROGEN: A CASE STUDY FROM THE DRY VALLEYS, SOUTHERN VICTORIA LAND, ANTARCTICA

Granitoids associated with the early Paleozoic Ross Orogeny are extensively exposed in the Dry Valleys region of southern Victoria Land, Antarctica, affording an exceptional opportunity to gain insight into the temporal and spatial scales of subduction-related magmatism. Although the current geochronologic dataset is sparse, it suggests a complex magmatic history that spanned at least 45 Ma in the southern Victoria Land segment of the Ross Orogen. Further U-Pb and Hf analysis of zircon, coupled with whole rock elemental and isotope geochemical data quantify (1) the time scale over which this subduction related magmatic system persisted, (2) spatial (both along and across orogenic strike) and temporal shifts in magma sources, and (3) variations in the magnitude of magmatic activity over time. A suite of over 30 new U-Pb zircon and titanite ages from the Dry Valleys area was obtained using the LA-MC-ICP-MS facility at the University of California, Santa Barbara. These ages more than double the existing data set for the crystallization and cooling ages of granitoids in the Dry Valleys area. Along- and across-strike sampling of distinct plutons yields a high density age dataset that spans ca. 495-505 Ma, indicating that the most voluminous pulse of magmatism in southern Victoria Land occurred over a relatively short geologic time-period of 10 Ma. Several samples yield individual concordant analyses that span > 40 Ma. Some age dispersion may be attributed to protracted crystallization of the granitoids, but such a large range likely indicates inheritance and complex multi-phase pluton emplacement. Work in progress is aimed at analyzing Hf isotopes in zircon to determine likely source components of the granitoids and track compositional shifts through time. This high-density sample set from geochemically diverse suites of igneous rocks greatly expands our knowledge of the dynamics of the Ross Orogeny and provides a unique opportunity to refine and elaborate upon existing models for subduction zone magmatism.