The Neotethyan Sanandaj‐Sirjan zone of Iran as an archetype for passive margin‐arc transitions

Abstract

The Sanandaj-Sirjan zone of Iran is a northwest trending orogenic belt immediately north of the Zagros suture, which represents the former position of the Neotethys Ocean. The zone contains the most extensive, best preserved record of key events in the formation and evolution of the Neotethys, from its birth in Late Paleozoic time through its demise during the mid-Tertiary collision of Arabia with Eurasia. The record includes rifting of continental fragments off of the northern margin of Gondwanaland, formation of facing passive continental margins, initiation of subduction along the northern margin, and progressive development of a continental magmatic arc. The latter two of these events are critical phases of the Wilson Cycle that, elsewhere in the world, are poorly preserved in the geologic record because of superimposed events. Our new synthesis reaffirms the similarity between this zone and various terranes to the north in Central Iran. Late Paleozoic rifting, preserved as A-type granites and accelerated subsidence, was followed by a phase of pronounced subsidence and shallow marine sedimentation in Permian through Triassic time, marking the formation and evolution of passive margins on both sides of the suture. Subduction and arc magmatism began in latest Triassic/Early Jurassic time, culminating at~170 Ma. The extinction of arc magmatism in this zone, and its shift northeastward to form the subparallel Urumieh-Dokhtar arc, occurred diachronously along strike, in Late Cretaceous or Paleogene time. Post-Cretaceous uplift transformed the zone from a primarily marine borderland into a marine archipelago that persisted until mid-Tertiary time.

Geochemical and isotopic evidence for Carboniferous rifting: mafic dykes in the central Sanandaj-Sirjan zone (Dorud-Azna, West Iran)

“…We suggest, therefore, that a major, potentially plume-related rift event is common in NW Iran and it is potentially related to mafic flood basalt magmatism in the northernmost Arabian plate (Stern et al 2014). The alkaline mafic dykes and the Dare-Hedavand metagabbro from the Dorud-Azna region in the central SSZ are the southernmost occurrences of the mafic anorogenic magmatism within the SSZ and predate the suggested main stage Permian rifting of the SSZ (Hassanzadeh & Wernicke 2016). Our preferred interpretation is that the alkaline dykes of the Dorud-Azna region formed during an initial stage of potentially plume-related rif ting and are associated with the intrusion of the Dare-Hedavand metagabbros (Fig.…”

Geochemical characteristics and conditions of formation of the Chah-Bazargan peraluminous granitic patches, ShahrBabak, Iran

“…A north-dipping Neotethys subduction zone beneath the Sanandaj-Sirjan plate was started approximately in the Bajocian (Middle Jurassic;Golonka 2004;Yousefirad 2011;Sheikholeslami 2015;Hassanzadeh & Wernicke 2016). The formation and evolution of the Neotethys started from Late Palaeozoic times (Hassanzadeh & Wernicke 2016). Therefore, the tectonic regime between the Arabian margin and Sanandaj-Sirjan plate altered from passive to convergent (Ricou 1994).…”

“…During Late Triassic-Early Jurassic times, several microplates were sutured to the Eurasian margin, closing the Palaeotethys Ocean (Golonka 2004). A north-dipping Neotethys subduction zone beneath the Sanandaj-Sirjan plate was started approximately in the Bajocian (Middle Jurassic;Golonka 2004;Yousefirad 2011;Sheikholeslami 2015;Hassanzadeh & Wernicke 2016). The formation and evolution of the Neotethys started from Late Palaeozoic times (Hassanzadeh & Wernicke 2016).…”

“…The Zagros is the largest mountain belt and the most active collisional orogen associ ated with Arabia/Eurasia convergence. It belongs to the AlpineHimalayan orogenic system that resulted from closure of the Neotethys Ocean during the Cenozoic (Alavi 1994;McQuarrie et al 2003;Mouthereau et al 2012;Hassanzadeh & Wernicke 2016). The tectonic history of these zones as part of the Tethyan region has been summarized by many authors (e.g., Berberian & King 1981;Alavi 1994;Omrani et al 2008;Khadivi et al 2012;Mouthereau et al 2012;Mohajjel & Fergusson 2014;Shafaii Moghadam et al 2014;Hassanzadeh & Wernicke 2016).…”

“…Southern Iran can be divided into a set of three parallel NW-SE trending tectonic zones including: the Zagros FoldThrust Belt, the Sanandaj-Sirjan Zone, and the TertiaryQuaternary Urumieh-Dokhtar magmatic arc (Alavi 1994;Mouthereau et al 2012;Mohajjel & Fergusson 2014;Hassanzadeh & Wernicke 2016), (Fig. 1).…”