Early Cambrian highly fractionated granite, Central Iran: Evidence for drifting of northern Gondwana and the evolution of the Proto-Tethys Ocean

Abstract

The Zarin granitic body is located in the eastern part of the Yazd Block in the Central Iran microcontinent. The granite has variable granular to mylonitic textures. New zircon U-Pb dating shows that the granitic rocks crystallized at 535–530 Ma. The pluton has high SiO2 abundances (72.1–77.5 wt%), K2O (4.4–6.3 wt%) and low MgO (0.2–0.7 wt%) contents, as well as high K2O/Na2O (1.10–1.97) and A/CNK (molar ratio of Al2O3/(CaO + Na2O + K2O)) 0.9–1.1 ratios, and is dominantly peraluminous. The granite is enriched in light rare earth elements (LREEs) relative to heavy REEs (HREEs), has negative Eu anomalies, and is extremely depleted in Nb, Ba, P, Ta and Ti. It is also characterized by variable but commonly high 87Sr/86Sr(i) (0.7018–0.7093) and negative εNd(i) values of −1.1 to −2.6. The geochemical features indicate that the rocks are highly fractionated I-type granite and have undergone extensive fractional crystallization of hornblende, biotite and feldspar. Results are consistent with melting of an evolved lower crust source during the subduction of the Proto-Tethys Ocean. The emplacement of the Zarin granite is contemporaneous with the extension of a Cadomian continental arc on the north side of Gondwana, that rifted away to create the Rheic Ocean to its south. Cadomian basement rocks in Iran are interpreted as an important link between western and eastern sectors of the Late Proterozoic-Early Paleozoic orogenic belts along the northern side of Gondwana, and the histories of the Rheic, Iapetus and Proto-Tethyan oceans