Mantle-derived high-K magmatic fluxes in northeast Iran arc: Constraints from zircon U-Pb-O-Hf and bulk rock major-trace elements and Sr-Nd-Pb isotopes

Most continental arcs are built up over a long time (>= 100 myr), and while subduction may be ongoing throughout this interval, magmatism appears to be highly episodic. This episodic behaviour is character-ized by high-flux magmatic events but an overall low rate of magmatism. The causes of high-flux mag-matic events (flare-ups) are enigmatic in many continental arcs. Bulk-rock Sr, Nd, and Pb isotopes, as well as zircon O and Hf isotopes, imply that the mantle and the continental crust can be involved in mag-matic flare-ups. However, the relative contributions of mantle vs. crust with changes in eruption rates can differ from arc to arc. The Cenozoic magmatic arcs of Iran, built on mature continental crust, are an excel-lent candidate for studying the geochemical-isotopic feedback of magmatic pulses to understand the trig-gers for a flare-up. Our new data constrain the timing of the flare-up in NE Iran to the Early to Middle Eocene (51-43 Ma). This flare-up is characterized by the outpouring of high-K calc-alkalic to shoshonitic magmas at -110 +/- 8 km3/myr -km. Geochemical modelling using the Arc Basalt Simulator version 300 shows that the high-K trachybasalts, moderately to extremely depleted in high-field strength elements, can be derived from the shallower (3.0 GPa; 870 degrees C) to deeper parts (5.0-5.4 GPa; 965-980 degrees C) of a sub -ducting slab with -1.0 to 5.5 % slab melt flux. Mixing modelling using Sr, Nd, and Pb isotope data indi-cates that the Torud mafic-intermediate magmatic rocks can be generated by adding -1% to <6% of slab components (50% AOC: 50% sediment) to an Indian MORB-like mantle. Our results suggest that the high magmatic fluxes in NE Iran were instigated mainly by Eocene slab steepening after Paleocene flat-slab subduction, resulting in enhanced upwelling and melting of a volatile-enriched asthenospheric mantle.(c) 2023 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

Automated summary

Most continental arcs have episodic behavior with high-flux magmatic events and overall low rate of magmatism. The causes of these events are still enigmatic. The Cenozoic magmatic arcs of Iran provide a good opportunity to study the geochemical and isotopic feedback of magmatic pulses. The high magmatic fluxes in NE Iran were mainly caused by Eocene slab steepening after Paleocene flat-slab subduction. Rating: 8/10