Zircon U-Pb dating, mineralogy and geochemical characteristics of the gabbro and gabbro-diorite bodies, Boein–Miandasht, western Iran

ABSTRACT

The Boein–Miandasht Complex (BMC) is a part of the Sanandaj–Sirjan metamorphic basement and is cut by gabbroic to granitoid bodies. These intrusive bodies comprise gabbro, gabbro–diorite associated with fine-grained, in part porphyritic leucocratic granitoids. Zircon U–Pb dating of representative gabbro–diorite samples yielded ages of 166.4 ± 1.8 Ma and 163.5 ± 6.3 Ma (Callovian, the latest stage of the Middle Jurassic). Mineral chemistry of the gabbro–diorites shows a homogeneous composition of the main minerals, main augite to diopside clinopyroxene and plagioclase (~An_17–59). Moreover, low Al_Z/TiO₂ ratios of the clinopyroxene grains suggest that the rocks were generated in a within-plate tectonic regime. The SiO₂ contents of the gabbro-diorite rocks are between 46.36 and 55.61 wt. %, Al₂O₃ ranges from 7.57 to 17.98 wt. %. The TiO₂ contents vary from 1.18 to 3.65 wt. %, Fe₂O₃ from 7.41 to 12.95 wt. %, the MgO ranges between 3.49 and 15.75 wt. %, Na₂O from 0.65 to 5.08 wt. % and K₂O from 0.48 to 1.08 wt. %. These rocks mostly plot in the alkali-gabbro field. Compared to chondrite are characterized by enrichment of LREEs over HREE, enrichment of LIL elements (e.g. Rb, Sr and Ba) and obvious positive anomalies of Nb and Ti. Based on the chemical composition, and mineral composition, this complex was generated in an extensional tectonic regime by partial melting of the hot asthenospheric mantle which is not more consistent with previous models which have suggested for SaSZ evolution in before.

KEYWORDS:

• Zircon dating
• extensional basin
• sanandaj–sirjan zone
• Boein–Miandasht complex

Acknowledgments

We acknowledge financial support from a partial scholarship provided by the Ministry of Science, Research and Technology, Islamic Republic of Iran to the first author during her research at the University of Salzburg, Austria. Special thanks are due to Gertrude Friedl for her support during mineral separation and to M. Fatehi for his help in the fieldwork. A part of this research was financially supported by JSPS KAKENHI grants no.17H01671 in Japan. This version much benefited from the Reviewers comments, Federico Rossetti and editor, Hadi Shafaii Moghadm.

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No potential conflict of interest was reported by the authors.

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Funding

This work was supported by the JSPS KAKENHI [17H01671,25303029].