Configuration and Timing of Collision Between Arabia and Eurasia in the Zagros Collision Zone, Fars, Southern Iran

Abstract

The configuration and timing of the Arabia‐Eurasia continental collision, part of the broader Alpine‐Himalayan collisional system, remains controversial. We conducted sandstone petrology, detrital zircon U‐Pb‐Hf isotopic and trace element analysis, and Cr‐spinel electron microprobe geochemical analysis of samples from Paleocene to Miocene peripheral foreland strata in interior Fars, southern Iran. These data were used to test competing models for ophiolite obduction and Arabia‐Eurasia collision. In addition, we applied these data to compare the history of outward and upward growth of the Zagros and Himalayan‐Tibetan segments of the Alpine‐Himalayan collisional orogenic belt. The first appearance of radiolarian‐rich chert conglomerate, 100–90 Ma detrital zircons with positive ɛHf(t) values from +1 to +20 and midocean ridge geochemical affinity, and suprasubduction zone (SSZ) affinity Cr‐spinel is in the lower and middle Sachun Formation. These data indicate that obduction occurred before deposition of the upper Maastrichtian‐lower Paleocene Sachun Formation and developed in an intra‐oceanic setting rather than an Arabia‐Eurasia collision setting. Abundant continental‐arc affinity detrital zircon with 180–160 Ma and 50–27 Ma age‐probability peaks and varied ɛHf(t) values are present in the upper Oligocene‐lower Miocene Razak and Agha Jari formations, indicating sedimentary overlap with Eurasia. SSZ‐affinity Cr‐spinel in all samples indicates that ophiolitic rocks were a continual source of detritus in the foreland basin since Paleocene. The depositional age of the basal Razak Formation is between 25.7 and 21.5 Ma. Therefore, we interpret that collision between Arabia and Eurasia must have been initiated before deposition of the Razak Formation.

Tectonics, Base‐Level Fluctuations, and Climate Impact on the Eocene to Present‐Day Erosional Pattern of the Arabia‐Eurasia Collision Zone (NNW Iranian Plateau and West Alborz Mountains)

“…Taken together, this scenario displays that the west Alborz landscape evolved predominantly through tectonic processes at least since ∼26 Ma (e.g., Cai et al., 2021; Koshnaw et al., 2019; McQuarrie & van Hinsbergen, 2013). The Caspian Sea‐level fluctuations under the significant influence of tectonic and the subsidiary role of climate impacted the exhumation and erosion pattern across the western Alborz from ∼10 to ∼2.8 Ma (Figure 7c).…”

“…Taken together, this scenario displays that the west Alborz landscape evolved predominantly through tectonic processes at least since ∼26 Ma (e.g., Cai et al, 2021;Koshnaw et al, 2019;McQuarrie & van Hinsbergen, 2013).…”

“…The timing of collision between the Arabian and Eurasian Plates has been debated and varies from Cretaceous to Miocene (e.g., M. Berberian, 1983; M. Berberian & King, 1981; Dercourt et al., 1986; Dewey et al., 1973; Hempton, 1985; Mohammadi et al., 2022; Mouthereau et al., 2012; Ziegler, 2001; Şengör, 1990). However, the recent studies based on detrital zircon geochronology and changes in detritus provenance suggest the Late Oligocene (∼26 Ma, e.g., Cai et al., 2021; Koshnaw et al., 2020). This collision geologically affected the Iranian Plateau and its margin (Allen et al., 2013; Hatzfeld & Molnar, 2010; Stern et al., 2021).…”

“…However, some researchers believe that the initial soft stage of collision between the Arabian and Eurasian Plates began at ∼40-35 Ma, which caused the beginning of exhumation in the Iranian Plateau and Alborz Mountain (e.g., Ballato et al, 2011;Madanipour et al, 2013;Rezaeian et al, 2012). Later, ∼26 Ma, the final collision (hard stage) of Arabian and Eurasian Plates (e.g., Cai et al, 2021;Koshnaw et al, 2020) caused an increase in exhumation, hence, erosion rates increased slightly until ∼10 Ma (Figure 7a). Meanwhile, the Paratethys fluctuations (the base-level of Alborz Mountain) were nearly constant (Popov et al, 2010; Figure 7b).…”

Low‐Temperature Thermochronologic Response to Magmatic Reheating: Insights From the Takab Metallogenic District of NW Iran, (Arabia‐Eurasia Collision Zone)

“…The Arabia‐Eurasia continental collision has led to the development of a large deformation zone that extends from the Caucasus to the Persian Gulf and from eastern Turkey to western Afghanistan (e.g., Hatzfeld & Molnar, 2010 and reference therein). Although the timing of collision in NW and central Iran is still debated, an increasing number of studies suggest that it must have occurred sometime between the latest Eocene (∼35 Ma; e.g., Allen & Armstrong, 2008; Ballato et al., 2011; Darin & Umhoefer, 2022; Mouthereau et al., 2012) and the early (∼27 Ma; Koshnaw et al., 2019; McQuarrie & van Hinsbergen, 2013: Pirouz et al., 2017) to late Oligocene (Cai et al., 2021; Gholami Zadeh et al., 2017). The collision zone includes prominent mountain chains (e.g., Zagros, Alborz, Kopeh‐Dagh, and Talesh Mountains) and large N‐S to NW‐SE and NE‐SW oriented strike‐slip fault systems that bound relatively rigid crustal blocks (Central Iran, Lut and Helmand blocks, south Caspian basin, and IP, Figure 1; e.g., Vernant et al., 2004).…”