Tectonic significance of the late Eocene (Bartonian) calc-alkaline granitoid body in the Marivan area, Zagros suture zone, northwest Iran

ABSTRACT

The Marivan granitoid body of the northern Sanandaj–Sirjan Zone (N-SaSZ) of northwest Iran was emplaced into Cretaceous sediments, and is associated with minor amounts of iron skarn-type mineralization along the contact between the intrusion and surrounding country rocks. The granitoids within the intrusion include (hornblende-rich) diorite, granodiorite, and granite phases, and zircon U–Pb dating of four samples from this intrusion indicate they were emplaced during the late Eocene (Bartonian; 37.7 ± 1.0 Ma). These plutonic rocks can be classified into two main types, granitic and dioritic rocks, according to petrography and whole-rock major element geochemistry. Both the granitic and dioritic rocks are high-K, and some of the granitic rocks have an I-type affinity and peraluminous to metaluminous compositions. Both the granitic and dioritic rocks have ε_Nd(t) values that cluster around zero (–3.3 to +3.0) and low ⁸⁷Sr/⁸⁶Sr_(i) values (0.7040–0.7076), suggesting derivation from a mafic juvenile crustal or depleted mantle source, which was possibly mafic calc-alkaline rocks or amphibolites within the lower crust. The new zircon U–Pb ages and petrological and geochemical data presented in this study suggest that the Palaeocene–early Eocene collision of the Arabian and Iranian plates caused the ascent and emplacement of hot mafic magma through a slab window into the crust. This increased the geothermal gradient within the root zone of the developing magmatic system at the base of the continental crust, causing the partial melting of lower crust in this region. This generated mafic to intermediate magmas that were either directly emplaced into the upper crust or mixed with varying amounts of upper crustal material prior to emplacement, which formed the diorite to leucogranite range of compositions within the Marivan granitoid intrusion.

KEYWORDS:

• Sanandaj–Sirjan zone
• Marivan
• I-type granite
• zircon U–Pb age
• collision zone magmatism
• Sr–Nd isotopic ratios

Acknowledgments

This paper forms part of the Master’s thesis of the first author undertaken at the University of Kurdistan (UOK). We would like to thank Koshi Yamamoto and Simon Wallis for assistance during LA–ICP–MS analysis and BSE–CL (SEM) imaging, respectively. H. Azizi thanks Institute for Space-Earth Environmental Research (ISEE), Nagoya University, for support during the summer of 2019 (Grant No. 201901005) and some of this work was supported by JSPS KAKENHI (Grant Nos. 25303029 and 17H01671). This version much improved based on F. Lucci and two anonymous reviewers’ critical comments.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

This work was supported by the Japan Society for the Promotion of Science [17H01671, 25303029]; ISEE grant (Nagoya University) [201901005].