Tectonic evolution of north‐eastern Tethyan Himalaya: Evidence from U–Pb geochronology and Hf isotopic geochemistry of detrital zircons

Abstract

It is well established that the Himalayan Orogen was formed by successive amalgamation of continental slices to the Eurasian continent, with the final collision of the Indian continent. The Upper Triassic Langjiexue Group on the north-eastern margin of the Tethyan Himalaya has been central to debates on the provenance with diverse models linking it with the northern India, Lhasa terrane, or multiple sources from surrounding terranes including Australia. In order to address this debate, here, we present U-Pb ages, trace element characteristics, and Hf isotope data of detrital zircons.The trace element data suggest that analysed zircons are mostly of igneous origin, with a broad affinity to mafic source rock, and some of the grains showing evidence for hydrothermal alteration. The zircon age spectra show distinct Permian to Triassic age peaks at 200-280 Ma with εHf(t) between −6.1 and 13.4, Neoproterozoic to Cambrian ages at 480-750 Ma with εHf(t) ranging from −24.7 to 8.5, and a broad Meso-to Neoproterozoic age range of 850-1,150 Ma with εHf(t) values of −8.1 to 10.1. The age spectra from the Langjiexue Group are in contrast with that of the Lhasa terrane which has pronounced age peaks of 300-325, 550-600, 1,150-1,350, and 1,750-1,900 Ma, suggesting that Lhasa might not be the source of Langjiexue Group detritus. In a similar way, north-western Australia and the Banda Arc are excluded as sources of the Langjiexue Group. The Hf model age spectra show distinct peaks of 750-800 and 1,200-1,300 Ma, and the second peak agrees with that of the Tethyan Himalaya. We infer that the basin of Langjiexue Group formed within the basement of Tethyan Himalaya in the Triassic and conclude that the sediments were deposited at the passive margin of northern Indian continent. Based on the results, we also propose the palaeogeographic evolution of the Himalayan Orogen.

Comparing the Upper Triassic Deep‐sea Flysch of the Shannan Terrane with the Coeval Shallow Shelf Sediments of the Tethys Himalaya, Southern Tibet

“…One proposes that the provenance is not related to the Indian continent (e.g., Li G W et al, 2010Li G W et al, , 2014Cai et al, 2016;Li X H et al, 2016;Wang et al, 2016;Li, 2019;Ma et al, 2019;Liu et al, 2020), while the other suggests an affinity of provenance with the Indian continent (Tethys Himalaya. e.g., Cao et al, 2018;Fang et al, 2018;Meng et al, 2019;Zhang et al, 2019). Surprisingly, the Late Permian-Triassic detrital zircons were newly discovered from three sandstone samples of the Qulonggongba Formation (QF) in shallow shelf sediments of the Tethys Himalaya (Nyalam and Tingri regions, southern Tibet) (Meng et al, 2019).…”

Diverse Structural Styles of the Northeastern Tethyan Himalaya in Southern Tibet Reveal the Early Collisional Tectonics of India and Asia

“…Second, the siliciclastic rocks of the Langjiexue fold‐thrust belt exhibit abyssal submarine fan facies with middle to inner fan siltstone, sandstone and few water channel sandstone lenses. Generally, the siliciclastic rocks of the Gyaca mélange, QDSZ and Langjiexue belt reveal similar lithologies, maximum depositional ages, detrital zircon age spectra and Hf isotopic compositions (Cao et al., 2018; Fang et al., 2019; Meng et al., 2019; J. G. Wang et al., 2016; Zhang et al., 2020), which indicate that these three units all belong to the Indian passive continental margin. Furthermore, in the southern Tethyan Himalaya, the coeval Late Triassic strata, including the Tulong Group and Qulonggongba and Derirong Formations from bottom to top, show sedimentary environments transitioning from lagoon to offshore and finally to coastal environments (Garzanti, 1999; Meng et al., 2019).…”

“…Trace fossils of paschichnion widely occur in sandstone and siltstone (Figure 5o). The bivalve fossil halobia in argillic slate (L. Q. Wang et al., 2013) indicate a Late Triassic age for the Songre Formation, which is identical to the youngest detrital zircon age population of 232–220 Ma of the sandstone samples (Fang et al., 2019; Zhang et al., 2020).…”