Bulk chemistry and Hf isotope ratios of the Almogholagh Intrusive Complex, western Iran: a consequence of an extensional tectonic regime in the Late Jurassic

Abstract

ABSTRACT The Almogholagh Intrusive Complex (AIC) in the central part of the Sanandaj-Sirjan zone (C-SaSZ) includes gabbros to granites. Zircon U-Pb dating of mafic, intermediate, and felsic intrusions yield age of 146 to 141 Ma (Late Jurassic-Early Cretaceous). Bulk chemistry shows a wide range for SiO2 (46.8 to 73.3 wt.%), MgO (0.08 to 8.95 wt.%), and Fe2O3(T) (0.47 to 9.25 wt.%) and also alkali elements ranging from 3.59 to 10.12 wt.%. These rocks are characterized by a high content of large-ion lithophile elements (LILEs; e.g. Rb, U, Th, and K) and LREEs with weak Nb and Ta negative anomalies, showing many similarities to an extensional setting. The 176Hf/177Hf ratios vary from 0.282802 to 0.282985 with positive εHf(t) values from + 1.67 to +10.74 (avg: 7.85). Trace-element and isotope ratios modelling indicate that the AIC mafic-intermediate rocks were generated by partial melting of spinel lherzolite and then underwent considerable crustal contamination. The present work in combination with previous data confirm an extensional tectonic regime for the northern part of the C-SaSZ during the Late Jurassic to Early Cretaceous. Magmatic differentiation with crustal contamination played a fundamental role in the wide compositional range from mafic to felsic types that formed the AIC.