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

摘要

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 +/- 10.0 Ma and 148.3 +/- 3.6 Ma, respectively, based on U-Pb zircon dating. The SiO2 contents of the Kangareh and Taghiabad rocks are similar and range from 45.5 to 51.5 wt.%, and the Al2O3 contents vary from 14 to 24 wt.%, 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 15 wt.%, whereas those of the Kangareh rocks range from 5 to 9 wt.%. The TiO2 concentrations of the Taghiabad samples are high (1-3 wt.%), and these rocks can be classified as high Ti and Fe rocks. The chemical compositions of the two bodies show some clear differences. Positive sNd(t) values (+ 3 to +8) and low initial Sr-87/Sr-86 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 (87)sr/(86)sr-Nd-143/Nd-144 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. (C) 2015 Elsevier B.V. All rights reserved.