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

• Published in: Geophysical research letters Vol. 48; no. 22
• Main Authors: Tang, Gong‐Jian, Cawood, Peter A., Wyman, Derek A., Dan, Wei, Wang, Qiang, Yang, Ya‐Nan
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 28.11.2021
• Subjects: Basins; Closures; detrital zircon; Geochemistry; Isotopes; Lava; Magma; magmatic gap; Ocean basins; Oceanic crust; Oceans; Paleoceanography; Pamir; Permian; Radiometric dating; Records; Subduction; Tethys; Western Kunlun; Zircon
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2021GL095192

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. Plain Language Summary The closure of oceanic basins is generally believed to result from oceanic subduction associated with development of arc magmatism. However, there are no magmatic arcs associated with the closure of some oceanic basins in the Paleo‐Tethys realm. In order to understand the detailed history of ocean basins in the Paleo‐Tethys oceans, we carry out an integrated in situ analysis of zircon U‐Pb age and Hf‐O isotopes, along with whole‐rock geochemistry for sedimentary, magmatic, and metamorphic records from the Mazar‐Kangxiwa suture zone in the western Kunlun‐Pamir that is widely regarded as the main Paleo‐Tethys Ocean suture. Our data reveals that there is no record of a magmatic arc associated with Paleo‐Tethys Ocean closure during the Permian (ca. 300–250 Ma). This Paleo‐Tethyan oceanic basin was closed by oceanic crust underthrusting, rather than oceanic subduction. Thus, not all Paleo‐Tethyan oceanic basins were closed by subduction with development of arc magmatism. We propose that widespread oceanic crust underthrusting accounts for the common absence of a magmatic arcs in oceanic basins of the Paleo‐Tethys realm. Key Points There is no record of a magmatic arc during oceanic basin closure in the Mazar‐Kangxiwa suture zone between ca. 300–250 Ma This Paleo‐Tethyan oceanic basin opened at ca. 340 Ma and closed by ca. 250 Ma Oceanic crust underthrusting was a potential mechanism to account for oceanic basin closure and the absence of a magmatic arc