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

Abstract

Detrital 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.