Age and origin of subvolcanic rocks from NE Iran: Link between magmatic “flare-up” and mineralization

Abstract

Paleogene igneous rocks from ∼600 km Quchan-Sabzevar-Torud magmatic belt include a thick pile of volcanic and pyroclastic rocks which intruded by younger felsic-mafic plutons. Various types of mineralization including Iron Oxide-Copper-Gold (e.g., Firouzeh mine) and porphyry Cu-Au deposits (e.g., Jalambadan mine) are associated with the Quchan-Sabzevar magmatism. In this study, we describe new zircon U-Pb ages and geochemical-isotopic data of the subvolcanic rocks from near the Firouzeh mine. The Firouzeh subvolcanic rocks consist of (quartz-bearing) monzosyenites, monzodiorites and monzonites. These rocks have typical calc-alkaline signature and are mainly metaluminous in nature. Subvolcanic rocks display enrichment in Light Rare Earth Elements (LREEs) with negative Eu anomaly. Enrichment in Large Ion Lithophile Elements (LILEs) and depletion in High-Field Strength Elements (HFSEs) are geochemical characteristics of these rocks. The Firouzeh volcanic rocks also display calc-alkaline signature and are metaluminous to peraluminous. Volcanic rocks show both enrichment in LREEs and LILEs, associated with negative Eu anomaly. Zircon U-Pb indicates ages of 43.2 ± 0.4, 42.1 ± 0.4 and 41.8 ± 0.4 Ma for monzosyenites, monzodiorites and monzonites respectively. Zircon epsilon Hf(t) shows average values of −1.49 for monzonites, +9.07 for monzodiorites and −1.06 for monzosyenites. The Hf model ages for these rocks are in the range of 850–730, 270–180 and 3150–450 Ma, respectively. Inherited zircons are abundant in monzonites and have variable Hf isotope values. The wide range of zircon εHf(t) values and abundance of inherited/xenocrystic zircons suggest a multiple source(s) for the generation of the Firouzeh subvolcanic rocks, including a mantle melt and an old crustal component. Xenocrystic zircons indicate complex crustal components. We suggest the NE Iran subvolcanic rocks including the Firouzeh igneous rocks, generated above the Sabzevar subduction zone. This subduction zone was active since Late Cretaceous time.