Abstract
Due to the unique location in the Ludong region, geochronological study of this area is essential for the understanding of the Cretaceous tectonic evolution of Eastern China. Sedimentary sequences interbedded with tuff layers unconformably overlay metamorphic rocks in the Sulu Orogen. This research presents a more reliable geochronological dataset of a tuff layer on Lingshan Island in Qingdao. A total of 103 valid age values from 216 zircon grains were obtained in three fresh tuff samples. Approximately 87% of these zircon ages are dated as the Early Cretaceous, and their peak ages shift from the Aptian stage to the Albian stage. The spatial-temporal relationship between the tuff and the Mesozoic igneous rocks of Eastern China indicate the impact of the Pacific Plate subduction beneath the Asian continent. Six Albian single detrital zircons have a weighted average age of 103.8 ± 1.4 Ma, with the youngest age (103.4 ± 1.4 Ma) constraining the maximum depositional age of the tuff layer. The age sequence of four sections on Lingshan Island is defined in this study: sections A and B belong to the Laiyang Group, and sections C and D are considered the Qingshan Group and were deposited in the Late Cretaceous. Two pre-Cretaceous zircon age peaks were also observed. These age peaks coincide with the magmatic and metamorphic ages preserved in the Sulu Orogen; thus, the Sulu Orogen is the provenance of the sedimentary rocks on Lingshan Island.
Highlights
Convergent plate margins are the sites of most intense geological processes, such as magmatism, metamorphism, crust-mantle interactions, and related tectonic activity
Tuff zircon geochronological data to further constrain the depositional age, and the spatial-temporal correlation between the strata exposed on Lingshan Island and the Mesozoic strata in the Jiaolai Basin
The Sulu Orogen is the eastern extension of the Qinling–Dabie Orogen (truncated by the Tancheng-Lujiang Fault (TLF)) and developed as the result of the continental collision between the North China Craton (NCC) and the Yangtze Craton (YC) in the Early Triassic[11,12,13] (Fig. 1A)
Summary
Detrital zircon geochronological research has become a hot topic of global research, as it has been widely used to constrain stratigraphic ages, perform provenance analysis, and provide the inverse analysis of tectonic thermal evolution[35,36,37,38,39,40]. Three peak ages were recorded for the early Cretaceous zircons: ~125.3 Ma, ~119.9 Ma, and ~111.0 Ma (Fig. 2). We observed two pre-Cretaceous zircon age peaks (Fig. 4), which indicate the prior occurrence of magmatic activity and metamorphism. Granitic orthogneiss with the protolith age of 780 to 570 Ma is widely distributed in the South Sulu Orogen, which indicates that Neoproterozoic magmatic activity was prevalent in the South China Plate[11,12,14,77,78,79]. Zhai et al (2005) suggested that the granite and neutral intrusive rocks formed in the North China Craton at 210 to 180 Ma85 These rocks may record the earliest evidence of lithospheric thinning and mantle hydrothermal activity that occurred after the collision of the Sulu Orogen[86]
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