Late Triassic foreland basin and Early Palaeozoic basement in the eastern Yidun Micro‐block and its tectonic implications for the eastern Palaeo‐Tethys

Abstract

Subduction polarity and collisional process are still controversial in the eastern Palaeo‐Tethys. On the basis of 1:50,000‐scale geological mapping at the Heni Township, zircon U–Pb geochronology and whole‐rock geochemistry were analysed for volcano‐sedimentary rocks in the eastern Yidun Micro‐block, Qinghai‐Tibet Plateau. Early Palaeozoic sequences were reported firstly in the eastern Yidun Micro‐block. Two populations of detrital zircon U–Pb ages (~525 Ma and 800–1,250 Ma) and deformation and metamorphic characteristics imply that the Early Palaeozoic sequences were deposited during the Cambrian to Silurian in the South China Block. The Early Palaeozoic sequences in the eastern Yidun Micro‐block were extruded by Cenozoic NW‐SE strike‐slip faults. Both the Late Triassic upper Tumugou and Lamaya formations yield four prominent peak ages of ~260 Ma, ~450 Ma, 750 ~ 780 Ma, and ~1,850 Ma. U–Pb ages of youngest detrital zircons (226.2 ± 1.0–224.7 ± 1.1 Ma), uppermost andestic tuff (216.1 ± 0.3 Ma) and intruded granitoids (~215 Ma) show that both the upper Tumugou and Lamaya formations were deposited during 225 ~ 216 Ma. Whole‐rock geochemistry indicates that all sandstone samples underwent moderate weathering and strong sorting and recycling. They were derived from felsic provenance, like volcano‐sedimentary rocks and granitoids in the western Yidun and Qiangtang micro‐blocks, indicative of pre‐Norian closure of the Jinshajiang Ocean. The closure gave rise to a foreland basin filled by the 225–216 Ma volcano‐sedimentary rocks in the eastern Yidun Micro‐block. The closure of the Jinshajiang Ocean also led to a scissor‐like closure of the Ganze‐Litang Ocean by clockwise rotation. Combining these with previous work, the Ganze‐Litang Ocean was a back‐arc basin resulted from eastward subduction of the Jinshajiang Ocean and had not undergone oceanic subduction.

Geochronology and petrogenesis of the early Silurian Zeluo mafic-ultramafic intrusion, eastern Tibet: implications for the tectonic setting and evolution of the eastern Proto-Tethys Ocean

“…From south to north (Figure 1), the Himalayan, Lhasa, Qiangtang, Songpan-Garze, and East Kunlun blocks constitute the central tectonic units of the Tibetan Plateau (Dewey et al, 1988;Zhu et al, 2013). These blocks assembled after the closure of the Proto-Tethys, the paleo-Tethys, and the neo-Tethys sutures (Pan et al, 2012;Zhao et al, 2018;Xu et al, 2021).…”

“…The Zhongza-Zhongdian terrane consists mainly of Paleozoic clastic and weakly metamorphosed carbonate lithologies, accompanied by a small amount of Neoproterozoic granitic gneisses and metamorphosed volcanic rocks (Xu et al, 2021).…”

“…However, Early Paleozoic sequences were identified in the eastern part of the Yidun terrane (i.e., O1t, Figure 3). The results of detrital zircon U-Pb radiometric dating and sediment source analysis indicates that the Yidun terrane was a part of the Yangtze plate in the Early Paleozoic, before being rifted apart during the Late Paleozoic (Xu et al, 2021). The Triassic volcano-sedimentary rocks are primarily divided into the Tumugou and Lamaya Formations (Figure 3).…”

“…The Tumugou and Lamaya Formations were deposited 225-216 Ma and were derived from the Qiangtang and Zhongza-Zhongdian terranes (Xu et al, 2021). The Zeluo ultramafic-mafic rocks are the focus of this study and have a fault-controlled contact with the Tumugou Formation and Triassic granite (Figure 3).…”

“…Tethys, also known as the Tethys Sea or Tethys Ocean, was proposed in 1893 by the Austrian geologist Eduard Suess (Sengör, 1984), as a vast Mesozoic paleo-ocean that separated the Gondwana continent in the south, from the Angolan paleo-continent in the north. Much research has been devoted to geological studies of the East Tethys tectonic belt, mainly on the Tibetan Plateau, due to the importance of this extensive tectonic belt for understanding past plate reconstructions and geodynamics (Reid et al, 2005;Yan et al, 2005;Jian et al, 2008;Hu et al, 2009;Jian et al, 2009a;Roger et al, 2010;Wang et al, 2012;Zi et al, 2012;Hu et al, 2013;Hu et al, 2014;Wang et al, 2016a;Li et al, 2017;Zhao et al, 2017;Zhao et al, 2018;Liu et al, 2019;Xu et al, 2021). Based on a multidisciplinary dataset, four Tethyan ocean basins have been recognised in Asia (Metcalfe, 2021), the Proto-Tethys (Sinian-Silurian), Paleo-Tethys (Middle Devonian-Late Triassic), Meso-Tethys (Middle Permian-Late Cretaceous) and the Ceno-Tethys (Late Middle Triassic-Eocene).…”