Petrogenesis of Dehsard felsic rocks in the southwest of Kerman, Iran: Inference for the evolution of Sanandaj-Sirjan zone

Abstract

The Upper Triassic Dehsard felsic rocks (DFR), leucocratic to hololeucocratic granitic rocks, are exposed in the southernmost of the Phanerozoic Sanandaj-Sirjan zone in the Zagros orogenic belt of south-Central Iran. They intruded into the Paleozoic Khabr and Rutchun metamorphic complexes that consist of marble, greenschist, calcschist and micaschist rocks. The DFR are cut through by monzonitic and dioritic dikes. Comprehensive petrological and geochemical studies disclosed DFR as a plagiogranite. They are calc-alkaline, metaluminous to slightly peraluminous I-type granitoids and exhibit enrichment in large ion lithophile elements (LILEs; e.g. Na, K, Rb, Ba) in contrast to the depletion of high field strength elements (HFSEs; e.g. Nb, Ta, P, Ti). Their chondrite normalized REE patterns show LREE enrichment [(La/Yb)N = 4.41–23.77] and unfractionated HREE [(Gd/Yb)N = 0.60 to 2.23] that suggest the lack of garnet during partial melting processes. The positive Eu anomalies advocate plagioclase accumulation. The low Nb, Ta, P2O5, TiO2 content, isotopic data, LREEs enrichment, various tectono-magmatic discrimination diagrams may point out the formation of DFR in a mature island arc environment through partial melting of metabasic source with contribution of some greywacke sediments and subduction-related volatiles. The partial melting occurred above garnet stability field. The involvement of variable amounts of oceanic sedimentary rocks especially greywackes in the melting processes in a mature island arc setting, as characterised by εNdt results ranging from +0.93 to −5.19 at 220 Ma, could also cause the DFR inclination toward active continental margin environment. It seems that the development of an island arc in an intra-oceanic setting must be happened prior to the Late Jurassic–Early Cretaceous time, while northward subduction of Neotethys oceanic crust was in progress under southern margin of the Central Iranian Microcontinents. Subsequent collision of the island arc with SSZ led to the tectonic proximity of the DFR into SSZ constituents. This approach gives us new intuition for the renovation of the geodynamic history of Sanandaj–Sirjan zone.