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When and how the Bangong-Nujiang Tethyan Ocean closed is a highly controversial subject. In this paper, we present a detailed study and review of the Cretaceous ophiolites, ocean islands, and flysch deposits in the middle and western segments of the Bangong-Nujiang suture zone (BNSZ), and the Cretaceous volcanic rocks, late Mesozoic sediments, and unconformities within the BNSZ and surrounding areas. Our aim was to reconstruct the spatial-temporal patterns of the closing of the middle and western segments of the Bangong-Nujiang Tethyan Ocean. Our conclusion is that the closure of the ocean started during the Late Jurassic and was mainly complete by the end of the Early Cretaceous. The closure of the ocean involved both 'longitudinal diachronous closure' from north to south and 'transverse diachronous closure' from east to west. The spatial-temporal patterns of the closure process can be summarized as follows: the development of the Bangong-Nujiang Tethyan oceanic lithosphere and its subduction started before the Late Jurassic; after the Late Jurassic, the ocean began to close because of the compressional regime surrounding the BNSZ; along the northern margin of the Bangong-Nujiang Tethyan Ocean, collisions involving the arcs, back-arc basins, and marginal basins of a multi-arc basin system first took place during the Late Jurassic-early Early Cretaceous, resulting in regional uplift and the regional unconformity along the northern margin of the ocean and in the Southern Qiangtang Terrane on the northern side of the ocean. However, the closure of the Bangong-Nujiang Tethyan Ocean cannot be attributed to these arc-arc and arc-continent collisions, because subduction and the development of the Bangong-Nujiang Tethyan oceanic lithosphere continued until the late Early Cretaceous. The gradual closure of the middle and western segments of Bangong-Nujiang Tethyan Ocean was diachronous from east to west, starting in the east in the middle Early Cretaceous, and being mainly complete by the end of the Early Cretaceous. The BNSZ and its surrounding areas underwent orogenic uplift during the Late Cretaceous. [ABSTRACT FROM AUTHOR]

This article reports the depositional environment and provenance for the Tianquanshan Formation in the Longmuco–Shuanghu–Lancangjiang suture zone, and uses these to better understand the tectonic evolution of this region. Zircons in the andesite of the Tianquanshan Formation yielded concordia ages of 246, 247, and 254 Ma, indicating that the Tianquanshan Formation formed during the late Permian–Early Triassic. The Tianquanshan Formation consists of flysch and ocean island rock assemblages, indicating that the Longmuco–Shuanghu–Lancangjiang Palaeo-Tethys Ocean continued to exist as a mature ocean in the late Permian–Early Triassic. The detrital zircons in the greywackes of the Tianquanshan Formation yielded peak ages of 470–620, 710–830, 910–1080, 1450–1660, and 2400–2650 Ma, indicating the provenance of the Tianquanshan Formation was either Indian Gondwana or terranes that have an affinity with Indian Gondwana in the Tibetan Plateau (i.e. the Southern Qiangtang, Lhasa, and Himalayan terranes). The Ordovician quartzites, Carboniferous sandstones, Carboniferous–Permian diamictites, and the Upper Permian–Lower Triassic greywackes in the Southern Qiangtang, Lhasa, and Himalayan terranes all contain detrital zircons with youngest ages of ca. 470 Ma, indicating their source areas have been in a stable tectonic environment since the Ordovician, and this inference is supported by the continuous deposition in a littoral–neritic passive margin in these regions from the Ordovician to the lower Permian. Combining the present results with regional geological data, we infer that the Southern Qiangtang, Lhasa, and Himalayan terranes were all in a stable passive continental margin along the northern part of Indian Gondwana during the long period from the Ordovician to the early Permian. At early Permian, because of the opening of the Neo-Tethys Ocean, the tectonic framework of this region underwent a marked change to a rifting and active environment. [ABSTRACT FROM PUBLISHER]

• Quality factor of the Namche Barwa area (NB) is as low as other areas in the eastern Tibetan plateau (ETP). • Stress drop of NB is one of the largest among other seismic active areas of ETP. • The canyon's local site effect of NB is significantly amplified at frequencies below 2.34 Hz. In this study, 427 seismic data for 42 aftershocks (2.5 ≤ M L ≤ 3.6) of the 2017 M S 6.9 Mainling earthquake recorded at 14 temporary seismic stations were used to study the source parameters, quality factor, and local site effects of the Namche Barwa area. We calculated the regionally averaged site- and distance-related components of high-frequency attenuation parameter for the area as 0.0294 ± 0.0094 s and 0.0001930 s/km, respectively. The generalized inversion technique was applied to determine the source spectrum of the aftershocks, the quality factor of the area, and the site amplification of the selected stations. The inverted stress drops (Δ σ) of the aftershocks ranged between 1.58 and 10.44 MPa, with an average of 5.0 MPa and a logarithmic standard deviation of log 10 0.21. The average Δ σ of the Mainling aftershocks is considerably larger than those of several large earthquakes that occurred in adjacent areas along the South-North Seismic Belt, including the 2008 Wenchuan aftershocks (0.52 MPa), 2013 Lushan aftershocks (3.13 MPa), and 2021 Yangbi aftershocks (1.02 MPa). The inverted quality factor of the Namche Barwa area was found to be Q (f) = 112.32 f 0.712, which is similar to those of adjacent areas. The calculated resonant frequencies of the 14 selected stations ranged from 0.5 to 2.3 Hz, and the corresponding amplifications ranged from 2.5 to 16.2. The site amplifications were clearly different from those determined for the extensively studied adjacent areas. [ABSTRACT FROM AUTHOR]

New zircon U–Pb ages, major- and trace-element data, and Hf isotopic compositions are presented for bimodal volcanic rocks of the Zhaga Formation (ZF) in the western–middle segment of the Bangong–Nujiang suture zone (BNSZ), northern Tibet. The genesis of these rocks is described, and implications for late-stage evolution of the Bangong–Nujiang Tethyan Ocean (BNTO) are considered. Detailed studies show that the ZF bimodal rocks, which occur as layers within a typical bathyal to abyssal flysch deposit, comprise MORB-type basalt that formed at a mid-ocean ridge, and low-K calc-alkaline A-type rhyolite derived from juvenile crust. The combination of MORB-type basalt, calc-alkaline A-type rhyolite, and bathyal to abyssal flysch deposits in the ZF leads us to propose that they formed as a result of ridge subduction. The A-type ZF rhyolites yield LA–ICP–MS zircon U–Pb ages of 118–112 Ma, indicating formation during the Early Cretaceous. Data from the present study, combined with regional geological data, indicate that the BNTO underwent conversion from ocean opening to ocean closure during the Late Jurassic–Early Cretaceous. The eastern segment of the BNTO closed during this period, while the western and western–middle segments were still at least partially open and active during the Early Cretaceous, accompanied by ridge subduction within the Bangong–Nujiang Tethyan Ocean. [ABSTRACT FROM AUTHOR]

Timing of the opening of the Meso-Tethys Ocean, represented by the Bangong–Nujiang Suture Zone on the Tibetan Plateau, remains controversial. Further research is required to understand the breakup of the northern Gondwana margin and the tectonic evolution of the Tethyan realm. In this study, we present petrography, U-Pb dating and Hf isotopic data for detrital zircons from Upper Carboniferous–Upper Permian strata in the South Qiangtang Terrane on the Tibetan Plateau. These data, together with data from previous literature, indicate a youngest detrital zircon age peak of ca. 550 Ma for Upper Carboniferous–Lower Permian strata. This is far older than the depositional age of ca. 300 Ma and indicates a source in the stable Gondwana Continent. Upper Permian strata yield younger ages (490–247 Ma) with peaks at ca. 460, 355, 290 and 260 Ma, indicating a source in the active South Qiangtang Terrane. Combined with the unconformity between the Lower and Upper Permian strata in the western South Qiangtang Terrane, we conclude that a significant change in sedimentary provenance occurred at 280–260 Ma. This provenance change might have resulted from the 300–279 Ma rifting magmatism on the northern Indian margin of Gondwana (e.g., South Qiangtang). The 300–279 Ma magmatism is interpreted to reflect the early stages of rifting, and the subsequent 280–260 Ma sedimentary provenance change is interpreted as the later stage, both of which established a complete Early–Middle Permian (300–260 Ma) rifting process that marks the opening of the Meso-Tethys Ocean. • A change in sedimentary provenance occurred at 280–260 Ma in the South Qiangtang. • This provenance change is associated with the 300–279 Ma rifting magmatism. • The 300–260 Ma rifting process marks the opening of the Meso-Tethys Ocean. [ABSTRACT FROM AUTHOR]