The Proto‐Zagros Foreland Basin in Lorestan, Western Iran: Insights From Multimineral Detrital Geothermochronometric and Trace Elemental Provenance Analysis

Abstract

AbstractDetrital zircon (DZ) U‐Pb geochronology is a widely used provenance tool that leverages bedrock age signatures of hinterland source terranes. However, complex sediment recycling of multicycle zircon and hinterland provinces with nondiagnostic U‐Pb ages represent possible pitfalls for provenance reconstructions. Additional biases pertain to source rock zircon fertilities and insensitivity to low‐ and medium‐grade tectonothermal events that do not result in zircon generation. To bridge these inherent biases and gaps in DZ U‐Pb provenance data sets and derive more comprehensive tectonic reconstruction, this study combined U‐Pb and trace element analyses on DZ, apatite, and rutile as well as zircon (U‐Th)/He analyses from the Proto‐Zagros foreland basin in western Iran to shed light on Late Cretaceous tectonic accretion along Arabia. Integrated multimineral, multimethod data sets record formation of a 110‐ to 85‐Ma island arc within Triassic mid‐oceanic ridge crust of the Neotethys ocean, simultaneous obduction starting in Santonian‐Early Campanian times, and inversion of the Arabian rift margin. Overall, integration of these techniques constrains provenance based on multiple independent criteria including crystallization age, cooling history, and petrogenic‐geodynamic environment. This approach not only more completely described provenance signatures but also helped avoid significant pitfalls. For example, while Triassic DZ U‐Pb ages might be mistaken as input from Eurasia, zircon trace element analysis reveals a MORB signature and attributes these DZ to Neotethyan oceanic rather than Eurasian continental origin, having fundamentally different paleogeographic/tectonic implications for the Arabia‐Eurasia collision. Moreover, detrital rutile and apatite resolve and characterize multiple Paleozoic‐Mesozoic thermotectonic events not recorded by DZ U‐Pb due to their largely amagmatic nature.