Two stages of magmatism at the northern edge of Gondwana (SE Iran): New insights into tectono-magmatic evolution from UPb zircon geochronology

Abstract

The magmatic and geochemical evolution of the Golgohar granitoids in the southern Sanandaj-Sirjan Zone (SE Iran) were investigated through zircon UPb ages, Hf isotopic analyses, and whole-rock chemistry, providing insights into their petrogenesis and tectonic context. The geochronological results revealed two distinct stages of magmatism: the late Neoproterozoic-early Cambrian (568.4 ± 7.3–535.9 ± 9 Ma) and the late Carboniferous (311.8 ± 5–305.8 ± 3.9 Ma). The Precambrian rocks are predominantly composed of granite, and the late Carboniferous rocks are primarily monzonite; both sheared, deformed and strongly shuffled together. The bulk-rock chemical characteristics of these rocks overlap to some extent, predominantly displaying peraluminous and calc-alkaline signatures with similar element abundances, though with subtle distinctions. Both rock suites show positive anomalies in Cs, Rb, Pb, U, and Th, and negative anomalies in Ba, Eu, Sr, Nb, and Ta, with the late Carboniferous samples exhibiting relatively greater enrichment in Cs, Ba, Sr, and Eu. The Precambrian rocks are characterized by arc-like affinities, whereas the late Carboniferous samples can be categorized as within-plate rocks. Despite the geochemical similarities, the zircon Hf isotopic compositions reflect different source materials. The Precambrian samples mostly yield negative Ɛ_Hf(t) values, with some positive inputs (−6.24 to +17.74) indicating a crustal contribution in their source. In contrast, the late Carboniferous zircon grains show dominant positive Ɛ_Hf(t) values (+5.86 to +12.93), suggesting a juvenile mantle source. The obtained isotopic data and geochemical results correspond the Precambrian rocks to the Prototethyan subduction along the northern edge of Gondwana and plausibly attribute the late Carboniferous samples to the early stages of Neotethyan rifting. The observed uniform geochemical characteristics suggest that the late Carboniferous rocks formed from a hybrid parental magma created by mixing the late Carboniferous mantle-derived melts with the Precambrian crustal materials.