Provenance investigation for the Cambrian-Ordovician strata from the northern margin of the western Yangtze Block: implications for locating the South China Block in Gondwana

摘要

We report new U-Pb isotopic data for detrital zircons from Cambrian-Ordovician strata on the northern margin of the western Yangtze Block, which together with published U-Pb isotopic data for coeval strata in the South China Block, provide critical constraints on the provenance of these sediments and further shed light on the early Palaeozoic position of the South China Block in the context of Gondwana. Detrital zircons in this study yield four major age peaks in the early Palaeoproterozoic, early Neoproterozoic, middle Neoproterozoic and late Neoproterozoic - early Palaeozoic. The dominant age population of 900-700 Ma matches well with magmatic ages from the nearby Panxi-Hannan Belt, which indicates that Cambrian-Ordovician sedimentary rocks in the western Yangtze Block were mainly of local derivation. However, compilations of detrital zircon ages for the Cambrian-Ordovician strata from the Cathaysia Block and the eastern Yangtze Block show that both blocks are dominated by late Mesoproterozoic- and early Neoproterozoic-aged detrital zircons, which suggests a remarkable exotic input with typical Gondwana signatures. According to the integrated detrital zircon age spectra of the Cambrian-Ordovician sedimentary rocks from the entire South China Block and palaeocurrent data, the South China Block should have been linked with North India and Western Australia within East Gondwana. Specifically, the Cathaysia Block was located adjacent to Western Australia, while the Yangtze Block was connected with North India.