Migration of the Palaeozoic Magmatic Front from Zagros to Alborz Mountains with Progressive Closure of the Palaeo-Tethys Ocean; Insights from Zagros Detrital Zircon U-Pb Age and Hf Isotopic Composition

The northwest-southeast-trending Zagros Fold-and Thrust Belt in south Iran resulted from the late Oligocene to the early Miocene collision of the Arabian and Central Iran blocks. The Zagros Palaeozoic basin holds the key to reveal the tectonic setting of the earlier stages in the development of the Tethyan realm. We aim to document the Palaeozoic tectonic environment of the Zagros Basin and provide critical constraints on the progressive closure of the Palaeo-Tethys. This work presents a combined detrital zircon U-Pb age and Hf isotopic composition from the Zagros and Alborz basins in an attempt to identify and date major geologic events along the southern margin of the Palaeo-Tethys and reconstruct the regional tectonic history of the northern margin of Gondwana-Land during the Ediacaran-early Palaeozoic interval. Detrital zircons U-Pb age and Hf-isotope ratio from Zagros second-cycle Devonian and third-cycle Permian sandstones and Alborz Palaeozoic strata indicate main magmatic flare-ups in the Arabian-Nubian Shield including the Tonian island arc magmatism, the Ediacaran post-orocline-tightening magmatism, the late Ediacaran-early Cambrian Protogonos continental arc magmatism. In addition, detrital zircons recorded the Ordovician continuation of the arc activity in the Protogonos during the early Palaeozoic. Therefore, repetitive recycling of the Neoproterozoic crystalline basement and related sedimentary cover of the Arabian-Nubian Shield, i.e., the Saharides, is a plausible source of the Devonian and Permian strata in Zagros. Our results show a close geological tie between Alborz and other Gondwana-Land-derived units in terms of Palaeozoic detritus sources which is in concordance with the location of the suture along the northern margin of the Alborz Mountains. Separation of the Alborz from the Sanandaj-Sirjan zone is accomplished by inserting from the east, the Central Iranian Blocks (Yazd, Posht-e Badam, Tabas, Lut) by strike-slip stacking and anti-clockwise rotation. This created the extensional zone of Northwest Iran.