Upper Neoproterozoic garnet-bearing granites in the Zeber-Kuh region from east central Iran micro plate: Implications for the magmatic evolution in the northern margin of Gondwanaland

Abstract

This paper reports, for the first time, on a garnet-bearing granite body at Zeber-Kuh and interprets its petrogenesis, age and tectonic setting within the context of the evolution of the Cadomian subduction system. The primary minerals imply an origin at pressures greater than 8–6 kbars (~ 25 km depth) and at temperatures above 700 °C with >10 % water. The Zeber-Kuh granite is in tectonic contact with neighboring rocks. This igneous body has average SiO2 of 71 wt. %, average Al2O3 of 14 wt. %, 3.1–3.6 wt. % Na2O, 3.0–6.2 wt. % K2O and 3.3–0.1 wt. % MgO. The granite is characterized by light rare earth element (LREE)-enrichment, relatively flat heavy rare earth element (HREE) patterns with a small negative Eu anomaly and moderately fractioned REE patterns [average (La/Yb)N = 11.32]. Decreasing Fe2O3T, MgO, CaO, TiO2, Ba, Eu and Sr with increasing SiO2 contents are consistent with fractional crystallization and can be related to fractionation of plagioclase, clinopyroxene, hornblende, and apatite. Two granite samples yielded U–Pb zircon ages of 533±3 and 534±6 Ma, which regionally correspond to the younger Cadomian magmatism. Cathodoluminescence images of zircon grains from the studied samples show well-developed oscillatory bands, typical of felsic magmas zircons, and Th/U ratios range from 0.79 to 0.45 with an average of 0.60. The REE patterns of the zircons show progressive enrichment from LREE to HREE with a positive Ce anomaly and a negative Eu anomaly.The garnet-bearing granite of Zeber-Kuh represents the final stage of Cadomian magmatism along an extensional continental arc adjacent to the northern active margin of Gondwanaland.