Tectonic evolution of the Meso-Tethys Ocean in the Jurassic: Birth, growth, and demise of a missing intra-oceanic arc

Abstract

Reconstructing ophiolite ages and tectonic attributes can elucidate ancient ocean tectonic evolution. We present petrological, chronological, geochemical, and isotopic data for Ritu and Dongco ophiolites (Bangong–Nujiang suture zone, Tibetan Plateau). The ∼171 Ma Ritu and ∼169 Ma Dongco diabase are derived from high-temperature, highly depleted mantle metasomatized by subduction fluids; they are similar to fore-arc basalts. The ∼165 Ma Ritu andesites, from enriched mantle metasomatized by subduction fluids and a small proportion of subduction sediment melts, have affinity with the oceanic plateau. The ∼161 Ma Ritu dacites and Dongco granodiorites arose via interaction between subduction sediment melts and the mantle wedge, and ∼158 Ma Dongco granites were derived from subduction oceanic plate metasomatized by subduction sediment melts; they are all similar to arc magmatic rocks. Their high Na2O and low K2O and Th contents, and depleted zircon εHf(t) values, differ from those of southern Qiangtang terrane continental arc magmatic rocks, indicating intra-oceanic origin. The Middle Jurassic diabase and regional contemporaneous fore-arc basalts and boninites likely formed during intra-oceanic subduction initiation. The Middle–Late Jurassic dacites, granodiorites, granites, and regional contemporaneous high-Mg andesites likely formed in a mature intra-oceanic arc. Therefore, the Meso-Tethys Ocean may contain a ∼1000 km intra-oceanic subduction zone with Middle–Late Jurassic mature intra-oceanic arc. Subduction initiation of the intra-oceanic subduction zone likely arose via subduction transference caused by collage of the oceanic plateau and southern Qiangtang terrane at ∼182–177 Ma. At ∼171–155 Ma, the intra-oceanic arc gradually formed fore-arc basalts, boninites, high-Mg andesites, and tholeiitic/calc-alkaline arc rocks, indicating final maturity. The intra-oceanic arc west section potentially collided with the southern Qiangtang terrane ∼155–145 Ma, while the middle section potentially lasted until Early Cretaceous. Our study constrains Meso-Tethys Ocean evolution, providing an important basis for the study of intra-oceanic arcs in orogenic belts.