The Missing Magmatic Arc in a Long-Lived Ocean From the Western Kunlun- Pamir Paleo-Tethys Realm

The evolution of the western Kunlun-Pamir region involved the opening and closing of several branches of the Paleo-Tethys Ocean, although the specific timing of these events is poorly constrained. Here, we present a synthesis of sedimentary, magmatic, and metamorphic records associated from the Mazar-Kangxiwa suture zone in the western Kunlun-Pamir that is generally regarded as the main Paleo-Tethys Ocean suture. These data show that the Paleo-Tethyan oceanic basin opened at ca. 340 Ma and closed by ca. 250 Ma, and there is no record of a magmatic arc between ca. 300–250 Ma. The absence of a magmatic arc was a result of oceanic crust underthrusting, rather than oceanic subduction, which is consistent with a narrow back-arc basin. Our study provides an important example of how an oceanic basin opened and closed without oceanic subduction, and highlights a potential mechanism to account for the absence of a magmatic arc.