Geochronology, provenance, and tectonic setting of the meta-sedimentary rocks from the North Shahrekord metamorphic Complex, Iran

Abstract

ABSTRACT The meta-sedimentary rocks from the North Shahrekord metamorphic Complex (NSMC) comprise micaschists, paragneisses, quartz-feldspathic schists, and marbles. Detrital zircons from the paragneisses yield ages of ca. 2811–507 Ma with most of the dated grains belonging to the Late Neoproterozoic to Cambrian, suggesting a maximum depositional age of the sedimentary protolith during the Late Ediacaran to the Early Cambrian times (543 ± 12 Ma). In contrast, detrital zircons from the quartz-feldspathic schists are mostly dominantly 692–577 Ma and a few at ca. 2369–703 Ma, suggesting that the maximum depositional age of 577 ± 9 Ma, Late Neoproterozoic. The age distribution of detrital zircons suggests that their main provenance was located within the Arabian-Nubian Shield and adjacent terranes. Rutiles from a paragneiss give a U-Pb lower-intercept age of 181 ± 3 Ma, indicating the occurrence of a high-pressure metamorphic event during the Early Jurassic. The trace element contents of the two rock units show enrichment in LREE relative to HREE and negative Eu anomalies, indicating upper continental crustal sources. The geochemical evidence (e.g. low to moderate Chemical Index of Alteration (CIA) and Plagioclase Index of Alteration, high Index of Compositional Variability (PIA), and low Th/U) suggests that the quartz-feldspathic schists and paragneisses originated from an immature, and immature to less mature, respectively, intermediate-felsic igneous source and their protolith experienced a simple sedimentary recycling history with relatively weak to moderate chemical weathering. Geochemical and petrographic data also suggest that the precursor to the quartz-feldspathic schists and paragneisses were deposited in a continental island arc and a back-arc basin setting, respectively. Our new data, including depositional age, provenance, and geochemical evidence, provide perspectives on palaeogeographic affinities (provenance of sediments with different weathering and recycling materials), and paleotectonic reconstructions (from arc to back-arc) of the Iranian basement, exposed in the Sanandaj-Sirjan Zone, during Ediacaran.