Tectonic Evolution of the Meso-Tethys Ocean: Insights from Geochemistry and Geochronology of the Jurassic ophiolitic complex in the Asa area, central Tibet

Although voluminous Jurassic ophiolites have been reported along the Bangong-Nujiang Suture Zone (BNSZ), the tectonic setting of ophiolites and the Jurassic evolution history of the Meso-Tethys Ocean remain mysterious. This study presents petrological, geochronological and geochemical data for newly discovered Jurassic ophiolitic complex in the Asa area, the Shiquanhe-Namco Ophiolite sub-belt (SNO sub-belt) of BNSZ. Detailed geological investigations and zircon U-Pb dating reveal that the Jurassic ophiolitic complex are composed of a suite of Mid-Late Jurassic (165-158 Ma) ophiolite and Early Jurassic gabbros (ca. 190 Ma). The Early Jurassic gabbros show affinities with island arc tholeiitic (IAT) basalts, which were derived from depleted mantle sources modified by oceanic slab-derived fluids and formed in a forearc settings. The Mid-Late Jurassic ophiolite mainly consists of peridotites, cumulate gabbros, isotropic gabbros, plagiogranites and greenschists. Whole-rock geochemical and zircon Hf isotopic data suggest that the Mid-Late Jurassic ophiolite formed in an intra-oceanicisland arc setting. Together, the Asa ophiolitic complex document magmatic processes from forearc extension to the development of intra-oceanicisland arc, confirming the occurrence of intra-oceanicsubduction system within the Meso-Tethys during the Jurassic. We tend to regard that both northward intra-oceanicsubduction and ocean-continent subduction were initiated during the Early Jurassic in the Meso-Tethys. During Mid-late Jurassic, a northward intra-oceanicarc-back-arc basin system developed in the Meso-Tethys, along with a continental forearc spreading basin resulting from northward ocean-continental subduction beneath the South Qiangtang terrane, producing the complex Jurassic ocean structure of the Meso-Tethys.