A late Permian–Triassic trench‐slope basin in the Central Qiangtang metamorphic belt, Northern Tibet: Stratigraphy, sedimentology, syndepositional deformation and tectonic implications

Abstract

Records of sedimentation and deformation in trench-slope basins contain valuable tectonic information about the associated oceanic subduction zone. Here, we present a multidisciplinary study on newly discovered late Permian-Triassic sedimentary successions in the >500-km-long Central Qiangtang metamorphic belt (CQMB) to better understand the type of basin and the concomitant tectonism. The Mayer Kangri succession contains lithofacies associations of submarine fan siliciclastic rocks, slope-environment limestone, deep marine chert and minor olistostromes from the forearc basin. The conodont assemblages and sandstone and andesite interlayers yield continuous stratigraphic ages from the Lopingian to middle Norian. The clastic sediments had two provenances, including the epicontinental arc in the North Qiangtang block (NQB) and synchronous volcanism in the accretionary wedge. Moreover, a large suite of the Anisian-early Carnian radiolarian cherts (>30 m thick) was discovered in the Lanling area. Regionally, the CQMB shows evident spatiotemporal variations in late Permian-Triassic sedimentation, with a general depositional trend of southward deepening and getting younger. The three identified subzones include a bathyal setting, a carbonate platform setting and a deep marine setting from north to south. These observations indicate that the late Permian-Triassic sedimentary successions in the CQMB were deposited in a trench-slope basin environment during the northward subduction of the Longmu Co-Shuanghu Tethys Ocean beneath the NQB. Generally, the CQMB and the concomitant trench-slope basin is among the well-preserved ancient analogs characterized by extensional tectonism.The syndepositional horst-graben-like structure, forearc basin-derived olistostromes, abyssal radiolarian cherts and synchronous volcanism provide new implications for the geological evolution of the trench-slope basin.

Coseismic and Postseismic Fault Kinematics of the July 22, 2020, Nima (Tibet) Ms6.6 Earthquake: Implications of the Forming Mechanism of the Active N‐S‐Trending Grabens in Qiangtang, Tibet

“…The ∼NE45°-striking West Yibug Caka fault was previously considered a graben-bounding normal fault (Taylor et al, 2003), but we here reinterpret it as a sinistral-slip-dominant fault linking the QRG and Yibug Caka graben in the north and south, respectively. The blueschist mélange of the central Qiangtang metamorphic belt and the Triassic detachment faults on its boundary (Liang et al, 2012(Liang et al, , 2021 were considered as key evidence of the active fault translation in the Yibug Caka fault zone (Kapp et al, 2003;Taylor et al, 2003), showing a ∼10 km horizontal offset along the West Yibug Caka fault. In addition, the West Yibug Caka fault and the East Yibug Caka sinistral fault surround the ideally rhomb-shaped Yibug Caka graben (also named pull-apart basin by Taylor et al, 2003) in the south.…”