Paleozoic Tectonic Setting and Paleogeographic Evolution of the Qin‐Fang Region, Southern South China Block: Detrital Zircon U‐Pb Geochronological and Hf Isotopic Constraints

Abstract

The thick Silurian siliciclastic sedimentary rocks in the Qin‐Fang region contrasting with their absence in surrounding regions have long been an enigma for the early Paleozoic geology of South China. Here we employ detrital zircon U‐Pb geochronology and Lu‐Hf isotope analysis of Cambrian to Devonian samples from the Qin‐Fang and adjacent regions to trace sedimentary provenance and to further constrain its tectonic setting. The similar age spectra of the Cambrian samples from both sides of the Qin‐Fang region imply that they should be derived from a common source(s), arguing against the presence of a Cambrian ocean in the Qin‐Fang region. However, the U‐Pb age patterns of these Cambrian samples, as well as from Silurian and Ordovician sandstones both from within and outside the Qin‐Fang region, differ significantly from those of a middle Devonian sample from the Qin‐Fang region, and Ordovician to upper Triassic samples from the Indochina Block. These results, in conjunction with regional geological information, indicate that the Yunkai Mountain, which is located adjacent to the Qin‐Fang region, must have been emerged above sea level in the middle Devonian. Meanwhile, it can also imply that the Qin‐Fang region should be a part of South China rather than being a segment of the Indochina Block. A two‐stage evolutionary history of the Qin‐Fang region is proposed, (1) an intracontinental basin mainly filled by materials eroded from east Gondwana and/or eastern Cathaysia Block during the early Paleozoic and (2) a foreland basin in the Yunkai Mountain region at least since the middle Devonian.

Detrital Zircon U‐Pb Age Distribution and Hf Isotopic Constraints From the Terrigenous Sediments of the Song Chay Suture Zone (NE Vietnam) and Their Paleogeographic Implications on the Eastern Paleo‐Tethys Evolution

“…The 900–1,000 Ma age group (11.5 ± 1.5%) appears as a subordinate cluster in the Song Chay mélange (Figure 8a). However, similar to the 550–600 Ma age group, no contemporary igneous rocks have been recognized in the adjacent regions, but this detrital zircon age group occurs widely in the Early Paleozoic sedimentary rocks of the inner part of the NE Vietnam nappe, IB, and Cathaysia block (C. Wang et al., 2016; Xia et al., 2016; X. Zhang et al., 2018; Zhou et al., 2018). However, the provenance of 900–1,000 Ma detrital zircons in our samples cannot be clarified because of the widespread occurrence of this age group and the high similarity of ε Hf (t) values, and model ages between them (Figures 8 and 9).…”

“…A contemporaneous magmatism also widely distributed in the northern Kontum Massif (e.g., Carter et al., 2001; Gardner et al., 2017; Hieu, Dung, et al., 2016; Jiang et al., 2020; Nagy et al., 2001; Roger et al., 2007). Moreover, 440–460 Ma detrital zircons have been found also in the SCB, as an example in the Paleozoic sequences of the Cathaysia block and the North margin of the Yangtze block, such as Qinling‐Dabie orogenic belt (Xu et al., 2013, 2014; X. Zhang et al., 2018; Zhu et al., 2017). Furthermore, Early Paleozoic granitic plutons are widely exposed in the SCB, including NE Vietnam (Roger et al., 2000; Song, 2017; Y. Wang et al., 2007, 2013).…”

“…The 900-1,000 Ma age group (11.5 ± 1.5%) appears as a subordinate cluster in the Song Chay mélange (Figure 8a). However, similar to the 550-600 Ma age group, no contemporary igneous rocks have been recognized in the adjacent regions, but this detrital zircon age group occurs widely in the Early Paleozoic sedimentary rocks of the inner part of the NE Vietnam nappe, IB, and Cathaysia block (C. Wang et al, 2016;Xia et al, 2016;X. Zhang et al, 2018;Zhou et al, 2018).…”

The Early Permian assembly of the Jiamusi Massif and Khanka Massif: Evidence from sediment sources

“…In general, the eastern margin of the Late Palaeozoic Jiamusi Massif experienced the transition from neritic to continental facies (Li, Liu, Zhao, Zhao, et al, 2020; Zhang et al, 2021). The Khanka Massif has a Precambrian crystalline basement (Khanchuk, Sakhno, & Alenicheva, 2010; Xu et al, 2018; Zhang et al, 2018; Zhou et al, 2012), which is covered by Palaeozoic‐Mesozoic clastic rocks, carbonate rocks, and volcanic rocks (Jia et al, 2004; Shao & Tang, 1995; Zhou et al, 2012). Devonian‐Carboniferous strata are mainly distributed in the eastern and southern margins of Khanka Massif, and are neritic and continental facies sedimentary rocks and volcanic‐plutonic rocks.…”

“…As the direct recorder of important events such as massif collision and basin‐mountain coupling, the Early Permian Erlongshan Formation clastic rocks in Mishan provide us with an important research carrier to clarify the source characteristics of sediments at the boundary of the two massifs, and then reveal the assembly relationship between the Early Permian Jiamusi Massif and the Khanka Massif. With the gradual maturity of detrital zircon U–Pb dating technology and the increasingly extensive information contained in it in recent years (Dickinson & Gehrels, 2008; Gehrels, 2014; Tang et al, 2006; Wan et al, 2007), we can compare the detrital zircon U–Pb dating data of sedimentary rocks with the ages of strata (bodies) in potential source areas around the study area (Fedo, 2003; Yao et al, 2017; Zhang et al, 2018). It provides a new and effective method for provenance analysis.…”