Detrital Zircon Ages Of The Mesoproterozoic Metasedimentary Rocks In The Southern Yili Block: Implications For Tectonic Affinities Of The Microcontinents In Sw Central Asian Orogenic Belt

The origins and Paleogeographic reconstruction of the Precambrian microcontinents in the Central Asian Orogenic Belt (CAOB) are essential for understanding the continental crustal evolution and mechanism of accretionary orogeny. The Yili Block is one of the Precambrian microcontinents in SW CAOB and is a key component of the Kazakhstan microcontinent whose amalgamation is not yet well understood. In this study, we present detrital zircon U-Pb ages of the metasedimentary rocks from the Tekesi Group in the southern Yili Block to constrain its Precambrian history and tectonic affinity. A total of 540 concordant U-Pb zircon ages from the metasedimentary rocks defined dominantly Meso- to Paleoproterozoic detritus (1.1-1.8 Ga) with minor early Paleoproterozoic to Neoarchean and Neoproterozoic components. These results are comparable to those obtained from the northern Yili, Chinese Central Tianshan and Kyrgyz North Tianshan blocks. On the basis of careful analysis on the inner textures of dated zircons, and comparing these new results with the previous studies on magmatic rocks, it is suggested that (1) the Tekesi Group most likely deposited during the latest Mesoproterozoic-earliest Neoproterozoic (1079-963 Ma); (2) the provenances of the Meso- to late Paleoproterozoic detritus might be in situ basement rocks of the Yili Block, or the Chinese Central Tianshan, Kyrgyz North Tianshan and even exotic cratonic plates (e.g., Central Australia, Laurentia); and (3) the early Paleoproterozoic to Neoarchean components may have been derived from old cratonic plates (e.g., Tarim, Siberia). In combination with the available detrital zircon ages and regional stratigraphic data, we propose that the southern Yili Block has close tectonic affinities with the northern Yili Block, Chinese Central Tianshan, and Kyrgyz North Tianshan, and these ribbon-like microcontinents once situated on the continental margins of the constituent cratonic plates (e.g., Tarim, Siberia, Central Australia, Laurentia) during the assembly and break-up of the Columbia and Rodinia supercontinents, therefore they may offer important clues for global reconstructions of supercontinent cycles.