Temporal changes in subduction- to collision-related magmatism in the Neotethyan orogen: The Southeast Iran example

Continental-arc igneous rock compositions change in response to the transition from subduction to collision and these changes can reveal how the crust, lithosphere and magma sources evolved. Neotethys-related Late Cretaceous to Pleistocene subduction-and collision-related magmatic rocks from the similar to 350 km long southeast Urumieh-Dokhtar Magmatic Belt (UDMB) of Iran provide an excellent natural laboratory to better understand these changes. These igneous rocks are well-exposed and moderately eroded to reveal a nearly complete record since subduction initiation at similar to 95 Ma. We analyzed new samples for major and trace elements (83 samples), Sr-Nd isotopic compositions (47 samples), and U-Pb zircon ages (26 samples) and compiled geochemical and geochronological data on the southeast segment of the UDMB. The geochronological data reveal two magmatic pulses at similar to 80-70 Ma and similar to 50-0 Ma. Important changes in magmatic compositions reflect initial collision with Arabia at similar to 32 Ma, changing from normal calc-alkaline to increasingly adakitic immediately after collision began. Five stages can be identified: 1) normal continental-arc magmatism during the Late Cretaceous; 2) arc quiescence in Paleocene and Early Eocene time; 3) Middle-Late Eocene extensional arc magmatism related to slab rollback; 4) early collision and crustal thickening during the Early Oligocene; and 5) slab breakoff, asthenospheric up -welling, and associated adakitic magmatism from Middle Miocene onward. Temporal changes in UDMB magmas reflect the response of the overriding plate to changes in the geometry of the subducting Neotethyan lithosphere and to collision between Arabia and Iran. Crustal thickening and arc narrowing during Miocene to Pleistocene post-collisional magmatism caused adakitic magmatism and associated Cu mineralization. Zircon O-Hf and apatite O isotopes as well as bulk-rock Nd isotopes of Cu-bearing adakitic rocks are similar to other barren rocks, but nearly all fertile rocks have higher Hf/Y, Eu/Eu*(n) in zircon and higher Sr/Y, V/Y, Eu/Eu*(n) in apatite than barren rocks.

Automated summary

Continental-arc igneous rock compositions change in response to the transition from subduction to collision, providing insights into the evolution of crust, lithosphere, and magma sources. The Urumieh-Dokhtar Magmatic Belt (UDMB) in Iran offers a natural laboratory to study these changes. Geochemical and geochronological data reveal different stages of magmatic activity, reflecting the processes of subduction, collision, and crustal thickening. The temporal changes in UDMB magmas are related to the response of the overriding plate to changes in the subduction geometry and collision events.