Upper Jurassic radiolarian assemblages and chert geochemistry of the Shiquanhe ophiolite, NW Tibet: Implications for the evolution of the Meso–Tethyan ocean

Evolution of the Meso-Tethyan Ocean (MTO) is a contentious issue. Ophiolites in the Bangong–Nujiang Suture Zone, Tibet, are important for deciphering the evolution of this ocean. Well-preserved Upper Jurassic (Tithonian) radiolarian assemblages have been recovered from bedded cherts in the Shiquanhe ophiolite in the western Shiquanhe–Namuco ophiolitic mélange zone (SNMZ). They include 83 species belonging to 51 genera, representing the most diverse radiolarian fauna yet documented in ophiolites along this suture zone. Together with radiometric ages, these assemblages indicate that the Shiquanhe ophiolite is no younger than late Tithonian. La_N/Ce_N and Ce/Ce* ratios of cherts are supportive of deposition in a mature oceanic basin close to a continental margin. Network analysis reveals that the radiolarian fauna is similar to other coeval assemblages across the entire Tethyan realm. Our study suggests that the ocean recorded by the ophiolite of the SNMZ existed from at least the Late Jurassic and developed into a mature oceanic basin with a marine connection to the Neo-Tethyan Ocean, rather than as a short-lived embryonic seaway as previously inferred.