A New Model for the Evolution of Tethys Oceans: Evidence from the Distribution of the Oceanic Plate Stratigraphy in the Central-Southern Tibetan Plateau

The orogenic belts of the Tibetan Plateau record the opening, evolution, and multiple ocean–continent transitions of the Proto-Tethys, Paleo-Tethys, and Neo-Tethys oceans. A widely accepted model for Tethyan evolution in Tibet suggests that chains of block sequentially rifted from Gondwana in the Southern Hemisphere drifted northward, successively forming the Proto-Tethys, Paleo-Tethys, Meso-Tethys, and Neo-Tethys oceans along their trailing margins, and then accreted to Laurentia in the Northern Hemisphere (“conveyor belt” or “book-flipping” style), ultimately completing the formation of the Tibetan continental assemblage in the early Cenozoic. Here we test this model through a reconstruction of the spatial and temporal distribution of oceanic plate stratigraphy (OPS) across the central and southern Tibetan Plateau .We systematically compile and analyze the lithologic assemblages of ophiolitic melanges and other oceanic crustal remnants from approximately 130 outcrops of different ages in the central-southern Tibetan Plateau, geochronologic data from 256 ophiolitic and related oceanic fragments, and associated radiolarian-bearing cherts. On this basis, we establish the first Phanerozoic OPS stratigraphic framework and spatiotemporal evolution model for the Tibetan orogenic system. Our integrative review reveals the following new discovery. The Bangonghu-Nujiang-Changning-Menglian Ocean was opened in the Ordovician and experienced the evolution from the Proto-, via Paleo- to Meso-Tethys, not opened in the Triassic as previously thought. It is because that the oceanic crustal remnants preserved along this suture zone yield ages from 470.8 Ma to 120 Ma (Middle Ordovician to Early Cretaceous). Particularily, along the area of Longmucuo-Shuanghu which is parallel and close to the north part of the Bangonghu-Nujiang Ocean, a giant subduction-accretion complex belt was identified with oceanic crust remnants of ages from 517.1 Ma to 217 Ma (Middle Cambrian to Late Triassic), based on geological mapping since 2000 The oceanic crust remnants include abundant ophiolite blocks and high-pressure to ultrahigh-pressure metamorphic rocks. This belt was previously attributed to the south Qiangtang Block. Consequently, about the evolution of the Tethys Ocean of the central and southern Tibet Plateau, we propose a bidirectional migration model to explain it and this model is different from the previously proposed 'conveyor belt' or 'book-flipping' models. In our new model, the earliest Proto-Tethys Ocean originated in the central part of the plateau along the Longmucuo-Shuanghu-Bangonghu-Nujiang-Changning-Menglian system (named it as a “Central Ocean”). Subsequently, the Paleo-Tethyan and Neo-Tethys oceans were opened in the north to the “Central Ocean” from the Devonian and then in the south to the “Central Ocean” from the late Permian.