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

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 Fe₂O_3(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.

KEYWORDS:

• Hf isotopes
• extensional setting
• almogholagh batholith
• Sanandaj-Sirjan zone
• Jurassic magmatism

Highlight

• Almogholagh Complex crystallized at 145–141 Ma (western Iran)

• Almogholagh was produced from the partial melting of spinel lherzolite mantle

• This mantle magma underwent considerable contamination during ascent.

• A extensional regime is proposed for the geotectonic setting.

Acknowledgements

We thank Prof. H. Azizi (University of Kurdistan) for on editing earlier versions of this manuscript and their constructive comments leading to important improvements on the manuscript. Chemical data, zircon ages and Hf isotope ratios were financially supported by the National Natural Science Foundation of China (41888101, 41822204), the National Key R and D Program of China (2017YFC0601206), the ‘Light of West China’ Program of Chinese Academy of Sciences (CAS) (2017-XBQNXZ-B-013, 2018-XBYJRC-003), and the Project of China-Pakistan Joint Research Center on Earth Sciences, CAS (131551KYSB20200021). This is a contribution to IGCP 662, IGCP 669 and IGCP 710.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/00206814.2022.2114020