U–Pb zircon ages and geochemistry of Kangareh and Taghiabad mafic bodies in northern Sanandaj–Sirjan Zone, Iran: Evidence for intra-oceanic arc and back-arc tectonic regime in Late Jurassic

Abstract

The northern Sanandaj–Sirjan Zone (SaSZ) in northwestern Iran contains several granitoid and gabbroic bodies that are parallel to the Zagros Suture zone in a northwest–southeast direction. The fine-grained Taghiabad gabbro and coarse-grained Kangareh gabbroic bodies southwest of the Ghorveh in the northern SaSZ were crystallized at 158.0±10.0Ma and 148.3±3.6Ma, respectively, based on U–Pb zircon dating. The SiO2 contents of the Kangareh and Taghiabad rocks are similar and range from 45.5 to 51.5wt.%, and the Al2O3 contents vary from 14 to 24wt.%, with high Mg number (Mg#=61–72% and 46–63%, respectively). The Taghiabad body has higher contents of TiO2, Fe2O3, and P2O5 than the Kangareh rocks. The Fe2O3 contents of the Taghiabad rocks vary from 6 to 15wt.%, whereas those of the Kangareh rocks range from 5 to 9wt.%. The TiO2 concentrations of the Taghiabad samples are high (1–3wt.%), and these rocks can be classified as high Ti and Fe rocks. The chemical compositions of the two bodies show some clear differences. Positive εNd(t) values (+3 to +8) and low initial 87Sr/86Sr ratios (0.7034 to 0.7054) indicate a depleted mantle source for both bodies. The variation and distribution of trace elements, REEs patterns, and initial 87Sr/86Sr–143Nd/144Nd ratios show that the Kangareh and Taghiabad bodies have high affinities to tholeiitic and alkaline magmatic series. These results suggest an arc and back-arc system regime in an intra-oceanic system than the Andean magmatic type regime for the origin of these bodies in the Middle to Late Jurassic period. These complexes merged with the northern SaSZ during accretion-type continental growth in the Late Jurassic.