Infant intra-oceanic arc magmatism due to initial subduction induced by oceanic plateau accretion: A case study of the Bangong Meso-Tethys, central Tibet, western China

• Published in: Gondwana research Vol. 79; pp. 110 - 124
• Main Authors: Yan, Li-Long, Zhang, Kai-Jun
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.03.2020
• Subjects: Accretion; Bangong suture zone; High-Mg magmatic rock; Intra-oceanic subduction; Jurassic; Meso-Tethys; Oceanic plateau; Tibet; Meso-Tethys; High-Mg magmatic rock; Jurassic; Accretion; Bangong suture zone; Intra-oceanic subduction; Tibet; Oceanic plateau
• ISSN: 1342-937X; 1878-0571
• DOI: 10.1016/j.gr.2019.08.008

The Meso-Tethyan oceanic plateaus are becoming conspicuous as giant units on the oceanic floor and have played important roles in both continental marginal orogenesis and Tethys oceanic evolution. In this study, we present mineralogical, geochronological, geochemical and Sm–Nd isotopic data for basaltic lavas from the Namco ophiolite and a high-Mg pillow lava–dyke–gabbro association from the Pengco ophiolite in central Tibet. Zircon U–Pb and Ar–Ar dating reveals that the Namco lavas erupted at ∼181 Ma while the Pengco boninitic association formed at ∼164 Ma. The Namco lavas display nearly flat rare-earth element (REE) patterns with no Nb–Ta depletions as well as high εNd values, characteristic of oceanic plateau lava. In contrast, the Pengco high-Mg rocks exhibit low REE concentrations below the normal mid-ocean ridge basalt (N-MORB), ubiquitous Nb–Ta depletions and low εNd values, and the dykes and gabbros are characterized by U-shape REE patterns, indicating that they could have derived from a depleted mantle source that was contaminated by sedimentary flux and marking a mid-Jurassic initial intra-oceanic arc magmatism erupted on the Early Jurassic Meso-Tethyan oceanic plateau represented by the Namco ophiolite. Our Pengco boninitic rocks, along with the literature data, indicate a 167–160 Ma boninitic-like initial intra-oceanic arc within the Bangong Meso-Tethys, running from the Shiquanhe area to the Naqu area with a length of ∼1000 km, which was uniformly built on the Early Jurassic Meso-Tethyan oceanic plateau. Our literature investigation also indicates a ∼175 Ma accretionary orogeny with distinct signature of the oceanic plateau involvements along the southern Qiangtang continental margin, which is manifested by regional metamorphic, magmatic and depositional records. We thus suggest that the accretion of the Early Jurassic Meso-Tethyan oceanic plateau onto the southern Qiangtang continental margin resulted in the extensive orogeny along the continental margin, jammed the subduction zone at ∼175 Ma and induced intra-oceanic subduction initiation as well as the intra-oceanic infant arc magmatism in the Meso-Tethys at ∼164 Ma. [Display omitted] •The Pengco high-Mg magmatic association in central Tibet was dated at ∼164 Ma.•They derived from a depleted mantle source contaminated by sedimentary flux.•They represent nascent intra-oceanic arc magmatism.•A mid-Jurassic infant intra-oceanic arc existed within the Bangong Meso-Tethys.•The arc could be induced by accretion of Early Jurassic oceanic plateau at ∼175 Ma.