Palaeotectonic reconstruction of sandstones from the Triassic Nakhlak Group in Central Iran, using U-Pb zircon dating
Subject Areas :
S.H. Hashemiazizi
1
()
peiman rezaie
2
(Department of Geology, University of Hormozgan)
Keywords: Central Iran, Palaeotethys, Triassic, UPb zircon dating, Nakhlak Group.,
Abstract :
The Triassic Nakhlak Group in Central Iran is an important sedimentary succession that helps us better understand the closure of Palaeotethys and the Eo-Cimmerian orogeny in the Middle East. The Nakhlak Group consists of the Alam (Olenekian to Middle Anisian), Baqoroq (?Upper Anisian to Middle Ladinian), and Ashin (Upper Ladinian to ? Carnian) formations, which are mainly composed of volcaniclastic sandstones, mixed siliciclastic conglomerates, and marine carbonates. Here we examine the detrital zircon UPb ages from the Nakhlak Group to determine its provenance and constrain its palaeotectonic position within the Palaeotethyan realm. Most detrital zircons from the Nakhlak Group are euhedral and subhedral with Permian–Triassic ages (ca. 280–240 Ma), indicating they likely came from the Silk Road Arc's Permian–Triassic magmatic rocks. Minor zircon populations show pre-Permian Palaeozoic ages, around 320 Ma and 480 Ma, which probably originated from the basement on which the magmatic arc developed. Zircon grains with Neoproterozoic–latest Mesoproterozoic (ca. 550–1100 Ma) and Palaeoproterozoic (ca. 1800–2200 Ma) ages are anhedral or rounded, with the latter being more prominent in the upper Baqoroq Formation (Middle Ladinian), suggesting the recycling of older sedimentary rocks. Sandstone petrography indicates an additional metamorphic provenance for this formation, possibly due to a tectonic uplift in the source area, resulting in the erosion of metamorphosed rocks with a northeast Gondwanan affinity. This suggests that northeast Gondwana-derived continental fragments likely belonging to the Cimmerian blocks had already arrived at the southern Eurasian margin in pre-Late Triassic time.
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