Collision Timing and Provenance Shifts from the Late Oligocene to Middle Miocene in the Southeasternmost Zagros Orogen.

Determining the timing of the initial continental collision is a fundamental step in accurately reconstructing the paleogeodynamic evolution of orogenic belts. This process necessitates a comprehensive integration of evidence gathered through various analytical techniques, both in the field and in the laboratory, to achieve a conclusive understanding. We here use comprehensive methods, including sandstone petrography, U-Pb dating, trace element and Hf isotopic compositions of the detrital zircon, in the Haji Abad (eastern Zagros Orogen) and the Shamil areas (west of the Minab-Zendan Fault) to constrain the timing of the initial collision between Arabia and Eurasia. Zircon U-Pb dating in the Haji Abad area reveals that detritus predominantly originates from the Arabia Pan-African basement (∼640 - 539 Ma, Ɛ (t): -10 to + 10) at the base of the Upper Oligocene-Lower Miocene Razak Formation. This is subsequently replaced up-section by detritus from Cenozoic and Mesozoic Eurasia magmatic-arc sources (~ 54 - 10 Ma, Ɛ (t): -2 to + 16; ~110 - 89 Ma, Ɛ (t): -2 to + 20, and ~ 175 - 163 Ma, Ɛ (t): -4 to + 10). In contrast, the Shamil area shows that detritus from the Pan-African Arabia basement remained dominant until the Early Miocene. The minimum age of continental collision is characterized by a significant change in provenance, transitioning from detritus sourced from the Arabia lower plate to that derived from the Eurasia upper plate. This transition is documented from the Late Oligocene in the Neyriz and Haji Abad areas along the Main Zagros Thrust, to the Middle Miocene (Langhian) in the Shamil area along the Minab-Zendan Fault.