Two ophiolite belts in the East Kunlun Orogenic Belt record evolution from the Proto-Tethys to Paleo-Tethys Oceans

As relics of oceanic lithosphere, ophiolites exposed in the East Kunlun region are crucial for deciphering the evolution from the Proto-Tethys to the Paleo-Tethys. Two ophiolite belts have been recognized in the East Kunlun Orogenic Belt: the northern Heishan-Dagele-Qingshuiquan Ophiolite Belt and the southern Muzitag-A'nyemaqen Ophiolite Belt. Most basaltic rocks in the northern ophiolite belt show apparent geochemical features of enriched mid-ocean ridge basalts, with some of suprasubduction zone-type affinity, and probably formed in arc to back-arc settings with ages of 537–406 Ma. Cumulates (wehrlites) and arc-related volcanics in these ophiolite complexes also display a subduction-related signature. However, most basalts in the southern ophiolite belt exhibit characteristics of mid-ocean ridge basalts and plume-related basalts, which are unrelated to subduction zone. The anhydrous troctolite outcrops in the southern belt also support this viewpoint. Statistics of all the available age data for the southern ophiolites indicate two cycles of seafloor spreading or plume activity, which gave rise to two main epochs of magmatic activity at 535–450 Ma and 345–308 Ma, respectively. The northern ophiolite belt recorded the evolution of the Proto-Tethys Ocean from at least the Early Cambrian to the Late Silurian. Based on geochronological and geochemical comparisons, the southern ophiolite belt shows similarities with the ophiolites in the Longmucuo-Shuanghu suture of Qiangtang on the south, which record the closure of Proto-Tethys Ocean and the opening of the Paleo-Tethys Ocean. The spatial and temporal distribution of the two ophiolite belts in the East Kunlun Orogenic Belt reveals the long-lived evolution from the Proto-Tethys to Paleo-Tethys system.