Pre-Cenozoic evolution of the Aghil Range (western Tibetan Plateau): A missing piece of the Tibet-Pamir-Karakorum geopuzzle

Abstract

The Tibetan Plateau, largely derived from the accretion of several Gondwana microplates to the southern margin of Asia since the late Palaeozoic, is the highest and largest topographic relief on Earth. Although the first order geodynamic processes responsible for its pre-Cenozoic evolution are quite well-known, many issues are still debated, among which is the timing of collision of each terrane with the southern margin of Asia. Even more uncertain is the pre-Palaeozoic history of these terranes, due to the lack of basement exposures. As a contribution to understanding the pre-Cenozoic evolution of the Tibetan Plateau, this paper focuses on the Aghil Range, a remote and poorly investigated area close to the Karakorum Fault between Kunlun and Karakorum (Xinjiang, China) in western Tibet. The tectono-metamorphic and magmatic evolution of the Aghil Range is investigated using a multidisciplinary approach that combines field mapping, petrology and geochronology (UPb on titanite, zircon, monazite and xenotime using SHRIMP-RG). We demonstrate that the Aghil Range preserves a coherent slice of Neoproterozoic crystalline basement with a late Palaeozoic sedimentary cover deposited on a passive continental margin during the Gondwana break-up. This represents the westernmost exposure of Precambrian crystalline basement known so far in the Tibetan Plateau. Furthermore, petrological and geochronological results allow reconstructing the Mesozoic poly-metamorphic evolution of this sector of the Tibetan Plateau, which records the evidence of Middle Jurassic (ca. 170 Ma) and Late Cretaceous (66 Ma) collisional events, as well as of the Late Jurassic (ca. 150 Ma) early subduction of an accretionary complex developed on its southern margin. Evidence of Late Cretaceous subduction-related magmatism preceding the last collisional event is also recorded. These results allow tentative correlation of the different terranes of Central Tibet with those of the Pamir-Karakorum Range on both sides of the Karakorum fault.