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The role of the Meso-Tethyan oceanic plateau in the growth of the Tibetan Plateau is debated. In this paper, we report coexistence of large-scale mid-ocean ridge basalt (MORB)-like and enormous ocean island basalt (OIB)-type mafic rocks from the Dongco ophiolitic rocks of the Bangong–Nujiang Suture Zone. The MORB-like rocks host tholeiitic geochemical characterizes, and have supra-subduction zone affinity such as enrichments in large ion lithophile elements (LILEs), depletions in high field strength elements, high ε Nd (t) values (+6.5 to +9.5) and low initial 87Sr/86Sr ratios (0.7033–0.7050). The OIB-type rocks have an alkaline affinity and are characterized by enrichments in LILEs and light rare earth elements, strongly negative Sr anomalies, variable ε Nd (t) values of −3.7 to +7.3, and low initial 87Sr/86Sr ratios ranging from 0.7034 to 0.7050. Metamorphic zircons from amphibolites in the sole of the ophiolitic rocks yielded U Pb ages of 104–100 Ma. Detrital zircons from the upper Cretaceous sandstone of the Abushan Formation (K 2 ab) yielded young U Pb ages of 100–86 Ma. Considering the regional geology, we suggest that the Dongco MORB-like rocks were derived from a depleted mantle source and formed from an intra-oceanic subduction-related setting, representing remnants of normal oceanic crust, whereas the OIB-type rocks were derived from an enriched mantle source representing remnants of a Meso-Tethyan oceanic plateau. Our preferred hypothesis is that the Meso-Tethyan oceanic plateau experienced a phase of accretion at 104–100 Ma, which probably increased local subduction erosion of the upper plate and providing provenance for the deposition of the K 2 ab sandstone. The maximum depositional ages of K 2 ab sandstone constraint the minimum ages for closure of the Bangong–Nujiang Tethys Ocean most likely at 100–86 Ma. • Identified a new 104 Ma metamorphic event in the western Bangong–Nujiang Suture • Closure of the Bangong–Nujiang Tethys Ocean most likely occurred during 100–86 Ma • Dongco ophiolitic rocks contain remnants of normal oceanic crust and oceanic plateau [ABSTRACT FROM AUTHOR]

The Mesozoic Meso-Tethyan oceanic plateaus could have played important roles in both Tibetan continental marginal orogenesis and Tethyan oceanic evolution. However, little has been known whether fragments of these tremendous oceanic highs underplated beneath the active southern Qiangtang margin and impinged on the later magmatic and/or tectonic evolution. The Anduo volcanic rocks of this study in the southern Qiangtang, erupted at 79.6 ± 0.8 Ma, comprise predominantly high-K trachyte and trachyandesite, including 5 adakites with high Sr and low Y and Yb contents and high La/Yb normalized to chondrite ratios (> 20). These high-K calc-alkaline and shoshonitic rocks, classified according to immobile trace elements, have enriched isotope compositions with (87Sr/86Sr) i = 0.7073–0.7079, ε Nd (t) = −1.78 to −3.90 and zircon ε Hf (t) = −1.3 to 1.4. Geochemical modeling reveals that the Late Cretaceous Anduo high-silica adakites were most likely derived from the melting of the mixed material of 80–90% of the subducted Meso-Tethyan oceanic plateau metabasalt with 10–20% of the subducted sediments. Variable negative Eu and Sr anomalies, relatively large range of Mg#, increases of the ε Nd (t) values with increasing Mg# and decreasing SiO 2 , and increases of (87Sr/86Sr) i with decreasing Mg# and increasing SiO 2 between adakites and non-adakites indicate the latter might have derived from lithospheric mantle assimilation and mineral fractional crystallization of the adakite parent magmas. It is thus concluded that the Meso-Tethyan oceanic plateaus could not only directly lead to the initial uplift of the Tibetan plateau through obduction and accretion onto the continental margin, but also contributed to the continental growth through relamination of the subducted oceanic plateaus. • The Anduo volcanic rocks in central Tibet were dated at 79.6 ± 0.8 Ma. • They are high-K trachyte and trachyandesite, including some high-silica adakites. • They have enriched Sr-Nd-Hf isotopes. • They were derived from melting of mixed material dominated by oceanic plateau. • Relamination of subducted oceanic plateau contributed to central Tibetan crust growth. [ABSTRACT FROM AUTHOR]

Shi et al. (2020) commented on our recent work (Li et al. 2019), which reconstructed the Wilson cycle of the Bangong-Nujiang Tethyan Ocean. They questioned our preferred latest Jurassic-Early Cretaceous Lhasa-Qiangtang initial collision model, and argued that the Bangong-Nujiang Tethyan Ocean did not close until the Late Cretaceous, based on the existence of Mid-Cretaceous OIB-type mafic rocks, arc-type magmatism and marine sedimentation as well as paleomagnetic data. Here we respond to all these pieces of evidence separately and eventually conclude that the observations and data they provided are not proof supporting the persistence of the Bangong-Nujiang Tethyan Ocean into the Late Cretaceous. Our preferred latest Jurassic-Early Cretaceous Lhasa-Qiangtang initial collision model thereby still holds. [ABSTRACT FROM AUTHOR]

We disagree the basic aspects regarding the evolution of the Bangong–Nujiang Meso-Tethyan Ocean (BNMTO) proposed by Li et al. (2019) (Earth-Science Reviews 198, doi: 10.1016/j.earscirev.2019.102907). Extensive Mid-Cretaceous ophiolite fragments and marine sedimentary rocks along the suture zone, along with Mid-Cretaceous magmatic arc (as late as 94 Ma) in the southern Qiangtang margin, indicates the BNMTO did not close until the Late Cretaceous, consistent with paleomagnetic data. Mid-Cretaceous OIB-type mafic rocks, covered by radiolarian-bearing cherts and being cold-emplaced ophiolitic fragments, together with Mid-Cretaceous magmatism of distinct arc affinity along the southern Qiangtang margin, indicate no magmatic evidence for divergent double subduction of the BNMTO. We also stress oceanic plateaus could have played a key role in the subduction evolution of the BNMTO. [ABSTRACT FROM AUTHOR]