The Ancestral Lhasa River: A Late Cretaceous trans-arc river that drained the proto–Tibetan Plateau

Abstract

Late Cretaceous trench basin strata were deposited in the subduction zone that consumed Neo-Tethyan oceanic lithosphere along the southern margin of the proto–Tibetan Plateau. We conducted detrital zircon (DZ) U-Pb geochronology on six trench basin samples (n = 1716) collected near Dênggar, Tibet (∼500 km west of Lhasa), to assess the provenance of these rocks and reconstruct Late Cretaceous sediment transport pathways. They contained DZ ages that point to a unique source around Lhasa city, north of the Late Cretaceous Gangdese magmatic arc. The modern Lhasa River catchment contains the requisite sources, and its main trunk transects the Gangdese magmatic arc, joining with the Yarlung River at a barbed junction at the India-Asia suture. We infer that the Lhasa River is an ancient feature that transported sediment to the subduction zone in Late Cretaceous time and persisted during India-Asia collision.

Cenozoic topography, monsoons and biodiversity conservation within the Tibetan Region: An evolving story

“…Despite this compression the northern part of the Lhasa terrane was maintained at an elevation no higher than 1 km until ~55 Ma by peneplanation, that is to say rivers laterally migrating, eroding and flushing out sediment in an overall arid landscape ( Hetzel et al., 2011 ; Strobl et al., 2012 ; Xu et al., 2015 ). One such river, the ancient Lhasa River, appears to have cut through the Gangdese highland ( Laskowski et al., 2019 ) until the rising Himalaya blocked it, most likely sometime in the late Eocene. This is marked by sedimentation in central Tibet switching from being fluvially-dominated to lacustrine, as evidenced by the contrasting dominant sedimentary facies of the Paleocene-Eocene Niubao Formation and Oligocene-Pliocene Dingqing Formation.…”

“…This barrier was most likely the Gangdese Mountains given that the ocean ‘moat’ between India and Eurasia no longer existed. However, the Gangdese barrier cannot have been complete and was likely penetrated by the ancestral Lhasa River ( Laskowski et al., 2019 ) until sometime in the Eocene (Section 2.3 ). Limited exchange with Indian taxa was possible through the deep connecting gorge, and it may have looked like the Tsangpo River gorge in SE Tibet today.…”

“…9 of Li et al., 2020c ) of its current position. After the transition from marine to non-marine sedimentation, the late Cretaceous through to early Paleogene environment along the BNSZ was arid, hosting dune fields but with flashy discharge rivers draining from the rising Gangdese and Qiangtang uplands ( Hetzel et al., 2011 ; Kapp and DeCelles, 2019 ; Laskowski et al., 2019 ; Strobl et al., 2012 ; Xu et al., 2015 ). The preservation potential for plant megafossils, especially leaves, in such dry and predominantly erosional conditions is very low, so we have to rely on surviving pollen and spore assemblages.…”

Discovery of Vestige Sedimentary Archives of the India‐Asia Collision in the Eastern Yarlung Zangbo Suture Zone

“…N is the number of igneous samples from Lhasa Terrane instead of analyzed zircon number. Data sources: Triassic sandstone of Lhasa Terrane compilation from Li et al (2014), Li et al (2016); the Rongmawa Fm within trench from Cai et al (2012), Wang et al (2018), Metcalf and Kapp (2019), Laskowski et al (2019); igneous rocks of Lhasa Terrane compilation from Wen et al (2008), Ji et al (2009), Zhu et al (2011), Zhu et al (2017), Zhu et al (2018), Zhang et al (2014), Wang, Wu, et al (2016), Zhao et al (2016), Li et al (2018), Zhou et al (2018), Zhang et al (2019); Triassic sandstone of NE Tethys Himalaya (Langjiexue Group, Shannan Terrane) from Aikman et al (2008), Aitchison et al (2011), Li et al (2010), Li et al (2016), and Webb et al (2013); Jiachala Fm of NE Tethys Himalaya from Wu et al (2014); Cretaceous sandstones of NE Tethys Himalaya from Hu et al (2010) and Hu et al (2012).…”

“…300 Ma) of the Upper Triassic shallow sea sequence (Figure 10) in the Lhasa Terrane (for details, see Li et al, 2016) and from the Cretaceous Rongmawa Fm (peak at ca. 215 Ma) in the trench basin within the YZSZ (Laskowski et al, 2019). Some researchers recently proposed that these 290–220‐Ma zircons could also have been derived from either an intraoceanic arc (Ma et al, 2019) or the continental arc in the Lhasa Terrane (Liu et al, 2020), but the absence of 1200 Ma age peak (Figure 10) and the identical morphology of zircon grains from both the Langxian unit and the Langjiexue Group, i.e., old (>500 Ma) zircons rounded and the young (~290–220 Ma) euhedral (Ma et al, 2019 and this work; Figure S3), favor the interpretation of the recycled detritus of the Langjiexue Group.…”