The convergence of plates since the Cenozoic era has had a profound impact on the paleogeography of Eurasia and the global climate. This process is mainly controlled by the convergence of the Indian, Arab, African plates and Eurasia, which not only leads to the westward closure of the New Tethys Sea, but also to the uplift of the orogenic belt in the Tethys Tectonic Domain, the strengthening of the East Asian monsoon, and the aridization of the mid-latitudes of the Asian inland. There have been many studies on the time, process and climatic effects of the collision between India and the Eurasian plate, but there is a great controversy about the collision time between the Arab plate and the Asian plate in West Asia, and there are different views such as late Cretaceous, late Eocene-Early Oligocene, early Miocene, Mesocene, Late Miocene collision, etc.; with the collision of plates and the decline in sea level caused by global climate cooling, the Tethys Strait between the Arabian Plate and the Asian continent is also eventually closed, but the closing time, process, and closure of the strait. The mechanism is also controversial. The existence of the above series of problems urgently requires more research from the Zagros orogenic Belt and the Foreland Basin.
Sun Jimin of the Key Laboratory of the Cenozoic Institute of Geology and Geophysics of the Chinese Academy of Sciences and his Iranian collaborators, with the support of the Foundation of the Basic Science Center of the National Natural Science Foundation of China and the Pilot Project of the Chinese Academy of Sciences, carried out comprehensive research on the Mesocene sea-land strata of the Zagros foreland basin of the Iranian Plateau in West Asia (Figure 1) with comprehensive research on sedimentology, biological stratigraphy, magnetic stratigraphy and tectonic geometry.
Figure 1 (a) Zagros tectonic unit division; (b) Dezful Embayment, where the study site is located in the lower disk of the leading edge fault
Based on the age of marine bivalve fossils and magnetic stratigraphy, they established a chronological framework of the study profile, indicating that the sedimentary age of the strata is 15-9 million years ago (Figure 2). Among them, the highest marine layer is 12.8 million years ago, which is consistent with the time of sea retreat they previously determined at the Lower Plate of the High Zagros Fault (Lurestan Arc), further indicating that the final closure time of the western section of the Tethys Strait is 12.8 Ma.
Figure 2 Magnetic stratigraphy results of the north wing of the anticline of the leading edge fault lower disk Gach-e Moh
They identified tectonic sedimentation (growth strata) in this study profile (Figure 3a), where changes in formation morphology clearly indicate the presence of growth strata and begin in the middle and upper parts of the Agha Jari Formation. Combined with the paleomagnetic age framework (Figure 3b), the base boundary age of the growth formation was determined to be 11Ma by linear interpolation between paleomagnetic age control points. Thus, the activity time of Zagros's leading edge fracture and its tectonic deformation of the lower disc was determined.
Figure 3 (a) Growth strata of the north wing of the Gach-e Moh anticline;
On the basis of the above research, combined with the research progress of predecessors, they proposed a conceptual model (Figure 4) to illustrate the corresponding changes in the timing, fracture activity, tectonic deformation, and sea-land distribution of the Arab-Asian plate collision process: (a) the end of the Oligocene - the Early Miocene (25-17 million years ago), although the Zagros main thrust fault has been active, but the southern edge of Asia is basically below sea level, at this time the land margin sea in central Asia and the Zagros Strait together constitute the vast land margin sea of the Iranian plateau. Shallow marine carbonate deposits were widespread; (b) In the Middle-Miocene (17-13 million years ago), land-land collisions between the Arabian plate and the Asian plate began at 17Ma, leading to the uplift of the southern edge of Asia (SSZ, UDMA) and the High Zagros fault activity. At this time, the sea waters in the central Iranian plateau withdrew, and during the period 17-13 million years ago, there was only a periodic (100,000-year-eccentric cycle of the Earth's orbit) in the Zagros foreland basin; around 13 million years ago, the Strait of Tethys was permanently closed; (c) during the Late Miocene 11 million years ago, the Zagros leading edge fracture began to be active, and the effects of the Arab-Asian plate collision were transmitted to desful Embayment.
Figure 4 Conceptual model
The research results were published in the international academic journals Tectonics (Sun Jimin*, Sheykh M, Windley B, Talebian M, Cao Mengmeng, Ahmadi N, Sha J G, 2022. Tectonics, DOI: 10.1029/2021TC006881）
Editor: Chen Feifei
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