Special issue on Mesozoic-Cenozoic tectono-magmatic evolution of Iran

The geodynamic evolution of Iran during Mesozoic-Cenozoic time is the story of formation and destruction of a convergent plate margin. This evolution has been controlled by the transition from oceanic subduction along the Zagros convergent margin to continental collision during late Eocene onward (Tadayon et al. 2019). Oceanic subduction was accompanied by Cretaceous supra-subduction magmatism and opening of oceanic back arc basins (Shafaii Moghadam et al. 2020) and Eocene magmatic flare-up (Verdel et al. 2011; Shafaii Moghadam et al. 2016; Rabiee et al. 2020) collision was accompanied by intense intraplate deformation in Central Iran (Nozaem et al. 2013; Calzolari et al. 2016; Tadayon et al. 2017) and controlled the distribution of vigorous syn- to post-collisional magmatism within the different tectonic domains of the Iranian region (Azizi and Moinevaziri 2009; Aghazadeh et al. 2010; Verdel et al. 2011; Allen et al. 2013; Pang et al. 2013; Castro et al. 2013; Neill et al. 2015; Shafaii Moghadam et al. 2016, 2020; Lechmann et al. 2018; Nouri et al. 2018; Rabiee et al. 2020). The Iranian region is thus an ideal natural laboratory to study and link the magmatic activity to the evolving geodynamic/tectonic scenarios along the Alpine-Himalayan convergence zone.

This special issue brings together diverse and comprehensive studies on the petrography, geochemistry, geochronology and tectonic setting of Mesozoic-Cenozoic magmatism in Iran, with the aim to better understand its tectono-magmatic and geodynamic evolution.

This special issue consists of eleven papers that report progress on Triassic magmatism in northeast Iran, Jurassic magmatism in the Sanandaj Sirjan zone (SaSZ), mid-Cretaceous sedimentation and Cenozoic magmatism in the Urmieh-Dokhtar magmatic belt (UDMB). The studied areas are indicated in Figure 1, along with the main litho-tectonic domains of Iran. Below, we briefly present and describe the papers published in this issue.

Figure 1. Simplified geology map of Iran(Stöcklin and Nabavi 1973). The studied areas for the papers are indicated.

(1) Zircon U–Pb geochronology, major-trace elements and Sr–Nd isotope geochemistry of Mashhad granodiorites (NE Iran) and their mafic microgranular enclaves: evidence for magma mixing and mingling. Authors: Deyhimi, M., Kananian, A., Mirnejad, H., Sepidbar, F., Vlastelic, I., Paquette, J.L. and Barbarin, B. This study reports new whole-rock geochemistry and Sr–Nd isotope systematics for the Mashhad granitoids and their mafic enclaves. Late Triassic U-Pb zircon crystallization ages are presented, framed within an emplacement scenario at the waning stage of the Paleo-Tethys closure.

(2) New evidence for Jurassic continental rifting in the northern Sanandaj Sirjan Zone, western Iran: the Ghalaylan seamount, southwest Ghorveh. Authors: Azizi, H., Nouri, F., Stern, R.J., Azizi, M., Lucci, F., Asahara, Y., Zarinkoub, M.H. and Chung, S.L. This study aims to elucidate the geodynamic environment controlling the Jurassic magmatism in the SaSZ by focusing on the Ghalayan metabasites of the Ghorveh area (northern SaSZ). These mafic rocks are enriched in LREEs without significant Nb, Ta, Pb, Sr and Ba anomalies, similar to modern continental intra-plate tholeiitic basalts of the Cenozoic East African Rift system. A continental rift setting is therefore proposed for Jurassic magmatism in the SaSZ.

(3) Zircon U-Pb dating, mineralogy and geochemical characteristics of the gabbro and gabbro-diorite bodies, Boein–Miandasht, western Iran. Authors: Tavakoli, N., Davoudian, A.R., Shabanian, N., Azizi, H., Neubauer, F., Asahara, Y. and Bernroider, M. The Boein–Miandasht intrusive rocks in central SaSZ comprise gabbros, gabbro–diorites with some granitoids with Jurassic zircon U-Pb ages of 166–163 Ma. These rocks are characterized by high TiO₂ (1.2 to 3.7 wt.%) and lack of Nb-Ta negative anomalies. These geochemical fingerprints together with the low Al/TiO₂ values of the mafic minerals are suggestive of an intraplate tectonic regime for generation of the Boein–Miandasht intrusive rocks during the Jurassic in the SaSZ.

(4) Makran ophiolitic basalts (SE Iran) record Late Cretaceous Neotethys plume-ridge interaction. Authors; Esmaeili, R., Xiao, W., Ebrahimi, M., Zhang, J.E., Zhang, Z., Abd El-Rahman, Y., Han, C., Wan, B., Ao, S., Song, D. and Shahabi, S. This paper reports whole rocks compositions and Sr-Nd-Pb isotope ratios of basaltic rocks from the Makran ophiolitic mélange complex. Four main magmatic groups are recognized: N-MORB, enriched-MORB, plume-type MORB and alkaline (OIB-like) basalts. Genesis of the OIB-like basaltic rocks is framed within an oceanic ridge with plume-ridge interaction in the late Cretaceous (at ~95 Ma).

(5) Syn-depositional continental rifting of the Southeastern Neo-Tethys margin during the Albian–Cenomanian: evidence from stratigraphic correlation; Authors; Navidtalab, A., Sarfi, M., Enayati-Bidgoli, A. and Yazdi-Moghadam, M. Based on the stratigraphic correlation between the Cretaceous successions (Kazhdumi and Sarvak formations) in the Zagros area and the development of several intra-shelf basins on the southeastern margin of Iran facing Neotethys, a continental rifting scenario is proposed during the Albian–Cenomanian.

(6) Geochemistry of arc-related mantle peridotites and gabbros from the Chaldoran ophiolite, NW Iran. Authors: Rezaei Bargoshadi, M., Moazzen, M. and Yang, T.N. This paper presents whole rock geochemistry of serpentinites-harzburgites and gabbroic lenses within peridotites from the Chaldoran ophiolites. Peridotites show low Al₂O₃, CaO, TiO₂, REEs, V and Y and high Ni, Cr and Mg, gabbros show low TiO₂ and Ti/V < 10. Formation in a fore-arc/proto-fore-arc environment is proposed to reflect Late Cretaceous subduction initiation of the Neo-Tethys.

(7) The middle Eocene high-K magmatism in Eastern Iran Magmatic Belt: constraints from U-Pb zircon geochronology and Sr-Nd isotopic ratios. Authors: Omidianfar, S., Monsef, I., Rahgoshay, M., Zheng, J. and Cousens, B. This paper focus on Cenozoic alkaline intrusive rocks exposed in East Iran, south of Birjand. Late Eocene magmatic ages (ca. 41–38 Ma) are reported, linking these magmatic products to the middle Eocene to late Oligocene Eastern Iran Magmatic Belt. Based on the whole rocks composition, isotope ratios and correlation with coeval igneous rocks in the eastern Iran, a post-collisional tectonic scenario (involving the Lut and Afghan block) dominated by lithosphere delamination is for the genesis of the middle Eocene to late Oligocene magmatism of the Eastern Iran Magmatic Belt.

(8) Geochemical and Sr–Nd isotopic constraints on the genesis of the Soheyle-PaKuh granitoid rocks (central Urumieh-Dokhtar magmatic belt, Iran). Authors: Sarjoughian, F., Javadi, S., Azizi, H., Ling, W., Asahara, Y. and Lentz, D. The Soheyle-Pakuh granitoids, with zircon U-Pb ages ~40 Ma, crop out in the central part of the UDMB. These granitoids are enriched in LILE (such as Cs, Rb, Ba, and K) along with low contents but depleted in HFSE (such as Nb, Ti, P). These geochemical fingerprints are similar to those of I-type arc-related granitoids formed in an active continental margin. These granites are juvenile, characterized by low ⁸⁷Sr/⁸⁶Sr (0.7043–0.7047) and positive εNd(t) values, ranging from +4.9 to +5.5. Slab rollback and (or) break-off, mantle upwelling, heat advection and underplating of mafic magmas were responsible for the partial melting of the juvenile lower crust and generation of granitoids during late Eocene.

(9) U-Pb zircon dating, Sr-Nd isotope and petrogenesis of Sarduiyeh granitoid in SE of the UDMA, Iran: implication for the source origin and magmatic evolution. Authors: Nazarinia, A., Mortazavi, M., Arvin, M., Hu, R., Zhao, C. and Poosti, M. The Sarduiyeh granitoids in southeastern segment of the UDMB have zircon U-Pb ages of ~28 Ma. These granitoids have calc alkaline I-type signatures and are enriched in LILE (such as K, Cs, Pb) and depleted in HFSE (such as Ti, Nb, Ta, Zr). It is proposed that these granitoids were formed by partial melting of the lower crust metabasites in an arc environment related to subduction.

(10) Geochemistry and zircon U-Pb geochronology of Miocene plutons in the Urumieh-Dokhtar magmatic arc, east Tafresh, Central Iran. Authors: Raeisi, D., Mirnejad, H., McFarlane, C., Sheibi, M. and Babazadeh, S. This paper reports on early Miocene (21–22 Ma) intrusive bodies from the Tafresh area in the UDMB. The Tafresh intrusives show high LILE/HFSE ratios and Nb-Ta negative anomalies. Geochemical signatures of the Tafresh plutonic rocks, such as a wide range of Y/Nb (2.7–8.4) and low Zr/Nb (19.5–35.) ratios, Nb/Ta (11.46–18.15), suggest for mantle–crust interaction during magma genesis, framed during the final stages of subduction-related magmatism prior to the collision between the Arabian and Eurasian plates.

(11) Olivine-hosted melt inclusions in Pliocene–Quaternary lavas from the Qorveh–Bijar volcanic belt, western Iran: implications for source lithology and cooling history. Authors: Salehi, N., Torkian, A. and Furman, T. This paper focus on silicate melt inclusions in olivine phenocrysts from the Pliocene–Quaternary basaltic rocks in the Qorveh–Bijar volcanic belt (northern SaSZ). An entrapment pressure of ~ 0.9–1.0 GPa and temperatures of ~1200–1350°C are estimated for the melt droplets in the olivine grains. A metasomatized pyroxenitic source is suggested to have contributed to the genesis of the parental melt. Convective removal and partial melting of the lithosphere is proposed to generate these basaltic rocks.

The papers published in this special issue document that three main tectonic/geodynamic scenarios controlled the Mesozoic-Cenozoic magmatic and tectonic evolution of Iran: (1) Jurassic continental rifting along the SaSZ, characterized by OIB-magmatism and S-type granite formation, followed by subsidence. (2) Late Cretaceous initiation of the Neotethys subduction along the Zagros convergent margin, which led to long-lived magmatism in the UDMB and in back-arc regions during the Cenozoic; and (3) Oligocene-Quaternary syn-collisional activity accompanying continued convergence with Arabia, reflecting involvement of sub-lithospheric mantle in magma genesis and Miocene-Quaternary alkaline magmatism.

Acknowledgments

We would like to thank Robert J. Stern for his continuous support and the reviewers for their help in manuscript evaluation.

Disclosure statement

No potential conflict of interest was reported by the authors.