Thermal-tectonic history of the İspir-Ulutaş porphyry Cu-Mo deposit, Eastern Pontides: Implications for regional tectonics and exploration of porphyry systems

Abstract

This study employs multiple low-temperature thermochronology techniques—Apatite Fission Track (AFT), Apatite (U-Th)/He (AHe), and Zircon (U-Th)/He (ZHe)—to reveal the cooling, exhumation, and preservation history of the İspir-Ulutaş porphyry Cu-Mo deposit, the oldest known porphyry deposit in the Eastern Pontides (∼131 Ma), and to investigate the relative scarcity of the porphyry systems in the Eastern Pontides.

The inverse thermal history model reveals a complex multi-stage cooling/exhumation history of the İspir-Ulutaş deposit. The ZHe data and thermal model indicate that the deposit was emplaced at a paleodepth of over 5 km at ∼ 131 Ma. The deposit experienced two major exhumation stages. The first, occurring during the Middle Eocene (∼43–38 Ma), was triggered by anomalous regional compressional forces likely due to the subduction of a mid-ocean ridge along the Bitlis-Zagros suture zone. During this phase, the porphyry system was exhumed to near-surface levels, but only its uppermost parts were eroded. Shortly after, post-collisional volcanic and sedimentary sequences buried the deposit, temporarily protecting it from further erosion. The second major exhumation phase, recorded by AHe data, began around 18 Ma and continues to the present, resulting in approximately 2.5 km of erosion. This phase aligns with the timing of the Arabia-Eurasia collision, which caused gradual uplift and exhumation across the region.

In summary, the deep emplacement of the İspir-Ulutaş deposit (>5 km), combined with the post-mineralization burial by Eocene sequences, extended slow exhumation, and drier/continental climatic conditions, played key roles in the preservation of the porphyry system. Lastly, the study proposes that areas in the southern Eastern Pontides, particularly those covered by Eocene sequences, may offer promising exploration targets for new porphyry deposits.