Aptian Flysch in Central Tibet: Constraints on the Timing of Closure of the Bangong‐Nujiang Tethyan Ocean

Abstract

The timing of the closure of the Bangong-Nujiang Tethyan Ocean is highly controversial. An important reason for this is that the sedimentological work within the Bangong-Nujiang suture zone is not sufficient. In this study, based on the U-Pb zircon dating of turbiditic sandstone and tuff interlayers, we determine the existence of Aptian flysch (ca. 126-113 Ma) in the middle and western segments of the Bangong-Nujiang suture zone. Further analysis shows that the Aptian flysch was deposited in a trench environment. In space, from the Mabujia Co area in the western segment to the Kama area in the middle segment, the outcrop extent of the Aptian flysch spans nearly 300 km from east to west. These results indicate that the Bangong-Nujiang Tethyan Ocean had not fully closed by the end of Aptian time, and its oceanic slab was still subducting. Based on this new discovery, and the results of previous studies, we believe that the middle and western segments of the Bangong-Nujiang Tethyan Ocean closed between 113 and ca. 92 Ma nonmarine deposition of the Jingzhushan Formation, which lies in angular unconformity above the flysch.

Early Cretaceous (∼138–134 Ma) Forearc Ophiolite and Tectonomagmatic Patterns in Central Tibet: Subduction Termination and Re‐initiation of Meso‐Tethys Ocean Caused by Collision of an Oceanic Plateau at the Continental Margin?

“…Marine sediment rocks Existence of oceanic basin (Baxter et al, 2009;Luo et al, 2020;Zhang et al, 2014Zhang et al, , 2012.…”

“…This view is consistent with recent high-quality paleomagnetic data obtained from western Tibet and covering the study area, which reveal: (a) a 2,600 ± 710 km and ∼825 ± 600 km width for the western Meso-Tethys Ocean during the Late Jurassic (∼160 Ma) and late Early Cretaceous (∼120-115 Ma), respectively (Cao et al, 2019(Cao et al, , 2020; and (b) the Lhasa Terrane drifted ∼8.5° northward from 123 ± 9 Ma to 97 ± 7 Ma and paleolatitudinally overlapped with the Qiangtang Terrane after ∼111-103 Ma (Chen et al, 2017;Meng et al, 2017). In addition, a recent integrated study of geological, sedimentological, and geochronological evidence has shown that Aptian deep-water deposits in the western BNSZ are analogous to those deposited in a trench basin rather than a peripheral foreland basin (Luo et al, 2020).…”

“…120–100 Ma; hereafter termed the “Cretaceous collision model”; e.g., Bao et al., 2007; Baxter et al., 2009; K. J. Zhang et al., 2012, 2014; Xu et al., 2015; J. J. Fan et al., 2018; W. Y. Chen et al., 2018; Luo et al., 2020; Shi et al., 2020). Conversely, researchers supporting the Jurassic collision model argue that these OIB‐type rocks represent partial melts of ascending sub‐lithospheric mantle in a post‐collisional extensional setting rather than Early Cretaceous oceanic crustal materials (P. Y. Hu et al., 2017; A. Ma & Hu, 2018; Zhu et al., 2016).…”

“…Fan et al, 2018;W. Y. Chen et al, 2018;Luo et al, 2020;Shi et al, 2020). Conversely, researchers supporting the Jurassic collision model argue that these OIB-type rocks represent partial melts of ascending sub-lithospheric mantle in a post-collisional extensional setting rather than Early Cretaceous oceanic crustal materials (P. Y.…”

Late Jurassic Nb‐enriched basalts from the Bilong Co area in the southern Qiangtang Terrane, central Tibet, and their implications

“…The Sm/Yb ratios can be used to distinguish between the partial melting of garnetand spinel-lherzolite sources, because magmas generated from a spinellherzolite source has nearly constant Sm/Yb ratios, where magmas from a garnet-lherzolite source will exhibit increased Sm/Yb ratios compared with the mantle source (Aldanmaz et al, 2000). The Bilong Co basalts have Sm/Yb ratios of 3.31-3.53, higher than those of the mantle array Qin, et al, 2014;Luo et al, 2020;Ma et al, 2017;Shi et al, 2020;G. Y.…”