INTEGRATING COMPLIMENTARY ACCESSORY PHASES (APATITE, RUTILE, ZIRCON) IN ISOTOPIC AND TRACE-ELEMENTAL PROVENANCE STUDIES: RECONSTRUCTING THE PROTO-ZAGROS OROGENY, NW IRAN

Detrital zircon (DZ) U-Pb geochronology is a powerful provenance tool but has recognized limitations in particular geologic settings due to variable zircon fertility among different rock types, the potential of non-unique source terrane ages, or complex recycling and mixing. However, integration of multiple analytical techniques and accessory phases can significantly improve resolution and amplify uniqueness of provenance signals and allow for a more detailed source characterization by utilizing multiple criteria such as crystallization age, cooling history, and petrogenic and geodynamic environment. In this study, U-Pb, trace-element, and (U-Th)/He analyses were applied to detrital zircon, rutile, and apatite from the Proto-Zagros foreland basin, which formed as a result of Cretaceous ophiolite obduction onto Arabia and was subsequently overprinted in the Arabia-Eurasia collision. These new integrated provenance results are used to test competing paleogeographic models and delineate the timing and nature of Protozagros unroofing. They reveal that Lower Cretaceous siliciclastic deposits in northern Arabia were strictly sourced from the Arabian-Nubian shield and East African orogenic belt. Maastrichtian-Paleocene strata record a major provenance shift; DZ trace-elements indicate major sediment influx from Triassic oceanic crust, whereas other proxies document arrival of detritus with diverse metamorphic and igneous signatures from the Eurasian continent, inverted Arabian rift margin, and a Cretaceous island arc. DZ thermochronometry constrains the major cooling and exhumation phase of these source units as late Campanian-Maastrichtian. Based on these new results, we present a reconstruction of the tectonic elements associated with the Proto-Zagros collision and discuss potential mechanisms for the occurrence of Eurasian sediments on Arabia ~30-40 myrs prior to the commonly-accepted timing for continental collision with Eurasia. Overall, the integration of complimentary detrital accessory phases and analytical techniques in the Proto-Zagros significantly enhances provenance reconstructions beyond traditional zircon U-Pb data and provides multiple criteria to assess the tectonic evolution of source terranes that have been eroded or overprinted by later events.