Resolving the nature and evolution of the Bangong−Nujiang Tethyan Ocean: New perspectives from the intraplate oceanic-island fragments preserved in Northern Tibet

Abstract

The nature and tectonic evolution of the Bangong−Nujiang Tethyan Ocean remain unresolved, which seriously restricts our understanding of the role of this ocean in the Tethys tectonic domain and hinders in-depth study of the geodynamics of the Tethyan tectonic evolution. The study of intraplate oceanic-island fragments in the Bangong−Nujiang Suture Zone of Northern Tibet, which are remnants of the oceanic crust, is important for determining the nature and tectonic evolution of the Bangong−Nujiang Tethyan Ocean. Here, we present a combined analysis of petrological, geochronological, geochemical, and Sr-Nd isotope data for the five intraplate oceanic-island fragments preserved in the Bangong−Nujiang Suture Zone. The oldest intraplate oceanic-island fragment in the Bangong−Nujiang Suture Zone is of Late Permian−Triassic age, and the underlying oceanic lithosphere is Late Permian or older, which indicates the development of the Bangong−Nujiang Tethyan Oceanic basin at this time. The opening time of the Bangong−Nujiang Tethyan Ocean must be even earlier than the Late Permian. At least four Triassic intraplate oceanic-island fragments have been recognized in the Bangong−Nujiang Suture Zone, and their assemblages and geochemistry are mostly similar to present-day oceanic-island basalts that erupted onto the thick lithosphere of mature oceanic basins. All of these observations indicate that the Bangong−Nujiang Tethyan Ocean evolved into a mature oceanic basin during the Triassic. The youngest intraplate oceanic-island fragments are of Late Jurassic−Early Cretaceous ages, which effectively argues for the continued presence of the Bangong−Nujiang Tethyan Ocean at this time. The abundant data of the intraplate oceanic-island fragments provide strong evidence that the Bangong−Nujiang Tethyan Ocean was a broad oceanic basin that separated Cimmeria from Gondwana during the Permian−Early Cretaceous and experienced complex evolution over at least 160 m.y.