Geochemical and Isotopic Evolution of Late Oligocene Magmatism in Quchan, NE Iran

Magmatic activity that accompanied the collision between Arabia and Eurasia at similar to 27 Ma, provides unique opportunities for understanding the triggers and magma reservoirs for collisional magmatism and its different styles in magmatic fronts and back-arcs. We present new ages and geochemical-isotopic results for magmatic rocks that formed during the collision between Arabia and Eurasia in NE Iran, which was a back-arc region to the main magmatic arcs of Iran. Our new zircon U-Pb ages indicate that collisional magmatism began at similar to 24 Ma in the NE Iran back-arc, although magmatism in this area started in the Late Cretaceous time and continued until the Pleistocene. The collisional igneous rocks are characteristically bimodal, and basaltic-andesitic and dacitic-rhyolitic components show significant isotopic differences; epsilon Nd(t) = +4.4 to +7.4 and epsilon Hf(t) = +5.4 to +9.5 for mafic rocks and epsilon Nd(t) = +0.2 to +8.4 and epsilon Hf(t) = +3.4 to +12.3 for silicic rocks. The isotopic values and modeling suggest that fractional crystallization and assimilation-fractional crystallization played important roles in the genesis of felsic rocks in the NE Iran collisional zone. Trace element and isotopic modeling further emphasize that the main triggers of the magmatism in NE Iran comprise a depleted to the enriched mantle and the Cadomian continental crust of Iran. Our results also emphasize the temporal magmatic variations in the NE Iran back-arc from Late Cretaceous to Pleistocene.

Automated summary

The study reveals that collisional magmatism in the NE Iran back-arc began around 24 million years ago, with magmatism starting as early as the Late Cretaceous and continuing until the Pleistocene. The collisional igneous rocks exhibit bimodal characteristics, with significant isotopic differences between basaltic-andesitic and dacitic-rhyolitic components, suggesting a role of fractional crystallization and assimilation-fractional crystallization in the genesis of felsic rocks. Trace element and isotopic modeling point to triggers of magmatism in NE Iran being a depleted to enriched mantle and the Cadomian continental crust of Iran, with temporal magmatic variations observed from Late Cretaceous to Pleistocene.