The first identified oceanic core complex in the Bangong–Nujiang suture zone, central Tibet: New insights into the early Mesozoic tectonic evolution of the Meso-Tethys Ocean

Abstract

In this paper, we report the first identified oceanic core complex (OCC) in the Saibucuo area of the Bangong-Nujiang suture zone, describe the geology and petrology of this OCC, and present new zircon U-Pb ages and Lu-Hf isotopes, and whole-rock major- and trace-elements and Sr-Nd isotopes for the diabase dikes in this OCC. The Saibucuo OCC consists of serpentinites, serpentinized peridotites, diabase dikes, tectonic breccias, sedimentary breccias, and limestones. The serpentinized peridotites cross-cut by carbonate veins, the sedimentary breccias with simple gravel compositions cut by normal faults, together with the limestones in the cover sequence lead to the conclusion that the Saibucuo OCC is similar to the OCCs of mid-ocean ridge settings. This conclusion is consistent with the E-MORB features of diabase dikes, which are formed by the interaction of the mid-ocean ridge and mantle plume, and the abyssal peridotite features of serpentinized peridotites. Zircon U–Pb ages of the diabase dikes indicate that the Saibucuo OCC was formed at the ca. 190 Ma. Based on these data and regional geological records, the early Mesozoic tectonic evolution of the Meso-Tethys Ocean was restored. The Meso-Tethys Ocean was a broad and mature oceanic basin during the Late Triassic-Early Jurassic. Coeval collision of the Northern and Southern Qiangtang terranes during the Late Triassic initiated the northward subduction of the Meso-Tethys Ocean, and the northward migration of the mid-ocean ridge. Continuous northward subduction of the Meso-Tethys Ocean caused the mid-ocean ridge to gradually approach the northward subduction zone, and eventually to subduct and collide with the northern trench during the Early-Middle Jurassic. The mid-ocean ridge within the Meso-Tethys Ocean was slow spreading during the Early Jurassic.