Detrital zircon U-Pb geochronology of early Cretaceous sedimentary rocks in Dingzi Bay and Taolin area from the Sulu Orogen: Provenances and tectonic implications

摘要

Early Cretaceous sedimentary rocks in the Sulu Orogen (SO) have been a popular topic in recent years. The provenances of sedimentary rocks can help elucidate the tectonic history of the SO, China. The Dingzi Bay and Taolin areas in the SO have always been poorly known. Thus, we date detrital zircons from four sedimentary rock samples including sandstone, siltstone, and greywacke collected in both areas. Age distributions from Dingzi Bay exhibit three major age populations including Palaeoproterozoic (1900-1800 Ma), Neoproterozoic (800-700 Ma), and Early Cretaceous (136-106 Ma) ages and small age populations including early Mesozoic, Palaeozoic, and Palaeoproterozoic-Archean ages, while age distributions in the Taolin area show the largest age population of Early Cretaceous (132-102 Ma) with minor early Mesozoic, Palaeozoic, and Neoproterozoic populations. The youngest detrital zircon populations yield weighted mean ages of ca. 116 Ma in Dingzi Bay and ca. 120 Ma in the Taolin area as the maximum depositional ages, which correspond to the Early Cretaceous Lower Qingshan Group. Age distributions in both areas indicate that the local SO served as the primary source area, whereas the Yangtze Block might have been a lesser source of detrital zircons. The comparison of geochronological, geochemical, and sedimentary data among Dingzi Bay, Taolin, Laoshan, and Lingshan Island suggests an Early Cretaceous marine basin formed over the SO. Further, considering previous regional tectonic history, we propose a two-stage (Laiyang and Qingshan stages) evolutionary model for this marine basin. We suggest that transpression between the Laiyang and Qingshan stages due to subduction of the Pacific Plate might have caused rapid uplift of the south-eastern SO and closing of the marine basin. Correspondingly, this process influenced the input of the source material from the Yangtze Block to the marine basin during the Qingshan stage.