Abstract
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.
Highlights
Rivers that drain the eastern Tibetan Plateau flow along intercontinental suture zones: the Yarlung along the India-Lhasa terrane suture, the Salween (Nagqu) along the Lhasa-Qiangtang suture, the Mekong along the Sibumasu-Indochina suture, and the Yangtze along the Qiangtang–Songpan-Ganzi suture (e.g., Brookfield, 1998; Zhang et al, 2019)
We present data (n = 1716) from six detrital zircon (DZ) samples from Late Cretaceous trench basin strata located near the town of Dênggar, ∼500 km west of Lhasa city (Fig. 1)
Our analysis reveals the distinct provenance of the trench basin and forearc basin strata, distinguished by the presence or absence of Late Triassic grains that were likely derived from the modern-day headwaters of the Lhasa River (Fig. 1)
Summary
Rivers that drain the eastern Tibetan Plateau flow along intercontinental suture zones: the Yarlung along the India-Lhasa terrane suture, the Salween (Nagqu) along the Lhasa-Qiangtang suture, the Mekong along the Sibumasu-Indochina suture, and the Yangtze along the Qiangtang–Songpan-Ganzi suture (e.g., Brookfield, 1998; Zhang et al, 2019). Despite reshaping and/or reorganization (Burrard and Hayden, 1907; Brookfield, 1998; Clark et al, 2004; Clift et al, 2006; Zhang et al, 2012; Zhang et al, 2019) during India-Asia collision (Yin and Harrison, 2000), the rivers remained pinned to the low-lying suture zones for millions of years. Its main trunk drains to the southwest across the Gangdese Mountains to the location where it meets the east-flowing Yarlung River at an abrupt junction with the acute angle on the downstream side (Fig. 1) This so-called barbed junction, along with lack of evidence for structural control along the trans-Gangdese segment (Harrison et al, 1992) and the observation of antecedent tributaries (Shackleton and Chang, 1988), suggests that the Lhasa River was established prior to tectonic uplift. Geological evidence for the hypothesized ancestral Lhasa River is lacking
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