TECTONO-MAGMATIC EPISODES IN IRAN: 32 YEARS AFTER THE PUBLICATION OF BERBERIAN AND BERBERIAN (1981)

The pioneering work of Berberian and Berberian (1981, Tectono-plutonic episodes in Iran: AGU/GSA Geodynamic Series, vol 3) was the earliest attempt to classify the vast plutonic rocks of the Iranian region in terms of geologic setting and from a plate tectonics point of view. The article was an inspiring accomplishment despite the paucity of relevant chemical and isotopic data at the time, and many of its insights and conclusions remain valid to this date.

The tectonic evolution of the Iranian segment of the Alpine-Himalayan orogenic belt reflects the geologically complex and protracted tectonic interactions between the Afro-Arabian (Gondwanan) and Eurasian plates along their Tethyan margins during the Phanerozoic time. Consequently, the bulk of magmatism in this region was associated with plate subduction, active margin development, continent-continent collision and post-collisional tectonism. A wealth of geochemical, petrogenetic and radioisotopic age studies in the past three decades have shed new light on the origin and tectonic setting of magmatism in Iran and adjacent regions. Here we summarize the implications of these studies for the major tectono-magmatic episodes in Iran.

The Neoproterozoic – Early Cambrian plutonic and volcanic rocks of the Iranian region were traditionally attributed to a continental rifting event, whereas modern studies link their origin to a Peri-Gondwanan marginal arc. Localized Late Paleozoic tholeiitic volcanism and intraplate plutonism in the region stemmed from crustal extension associated with the opening of the Paleo-Tethys Ocean. The Late Triassic plutonism remains poorly understood in terms of extent and origin, with recent studies suggesting a collisional setting for at least some intrusions. Middle to Late Jurassic, supra-subduction granitoid plutons in southwestern Iran perhaps mark the most voluminous magmatic episode in the region that locally continued into the Cretaceous. Subduction-related magmatism resumed with an enigmatic pause in Eocene farther inland, concomitant with crustal extension and core complex formation in the back-arc region, and culminated in the Neogene Arabia-Eurasia collision along the Zagros Orogen. Isolated Pliocene-Quaternary volcanism with alkaline affinities is related to the continued post-collisional convergence.