Early Triassic initial collision between the North China and South China blocks in the eastern Qinling Orogenic Belt

Highlights

• An Early Triassic provenance change was recognized from the Zigui and Dangyang basins.

• These basins started to receive sediments from Qinling Orogen during the late Early Triassic.

• Tectonic subsidence analysis denotes a basement uplift in the Middle Triassic

• Initial collision between South China and North China in eastern Qinling occurred during the Early Triassic.

Abstract

The closure of Mianlue Ocean lead to the collisional assembly between the North China Block (NCB) and the South China Block (SCB). But the timing of initial continental collision remains unclear, with the proposed ages ranging from the Late Permian to the Late Triassic. This study presents stratigraphic, sedimentological, tectonic subsidence, and provenance data from the Triassic strata in the Zigui and Dangyang basins lying along the eastern Qinling Orogenic Belt. These data document a tectonic transition in the central northern-SCB, and locally provide constraints on the timing of initial SCB–NCB collision. The Lower Triassic Daye Formation was deposited in a marginal basin to slope environment, and consists of mudrocks containing detrital zircons with major age peaks at ca. 1900 and 850 Ma. The overlying Lower Triassic Jialingjiang Formation comprises a shallowing carbonate sequence, with intercalated evaporites at the top of the formation. It contains mudrocks that are rich in detrital zircons with of ca. 270‐–245 Ma. The mixed carbonate and siliciclastic sequences of the Middle–Upper Triassic Badong Formation records tectonic uplift at its base, and contains detrital zircons with UPb age peaks at ca. 2500, 1850, 920–800, 450 and 350–220 Ma. Combined with petrographical observations and tectonic subsidence calculation, these detrital zircon UPb ages record a significant provenance change from recycled material derived from the SCB to newly generated detrital material from the NCB. This provenance change records the initial SCB–NCB collision in the eastern Qinling Orogenic Belt during the Early Triassic.

Introduction

The collision between the North China (NCB; also known as the Sino-Korean Block) and South China (SCB) blocks during the Permo–Triassic played a key role in the tectonic assembly of eastern Asia (Ames et al., 1993; Chang and Zhao, 2012; Enkin et al., 1992b; Kwon et al., 2009; Mattauer et al., 1985; Yin and Nie, 1993; Zhao and Coe, 1987). The collision denoted closure of the Mianlue Ocean which was a branch of the Paleo-tethys Ocean and subsequently the formation of the Qinling–Dabie Orogenic Belt (Dong and Santosh, 2016; Liu et al., 2015; Meng and Zhang, 1999; Ratschbacher et al., 2003; Zhang et al., 2004). Various types of evidence have been used to constrain the timing of collision (Table 1) and proposed variable ages for the collision, ranging from the Late Permian (Ames et al., 1993; Hu et al., 2020; Li et al., 1993; Ratschbacher et al., 2003; Yin and Nie, 1993; Zhang, 1997; Zhao and Coe, 1987), through the Early Triassic (Li et al., 2007; Meng and Zhang, 2000; Wang et al., 2019) and the Middle Triassic (Dong and Santosh, 2016; Jian et al., 2019; Lai et al., 2010; Liu et al., 2015), to the Late Triassic (Li et al., 2018a; Liang et al., 2015; Shi et al., 2012; Sun et al., 2002; Weislogel et al., 2006; Xu et al., 2014; Zhang et al., 2002). The variable ages relate to two issues. The first is the possible diachronous amalgamation of the NCB and the SCB (Meng and Zhang, 2000). Both indentation (Yin and Nie, 1993) and oblique subduction (Liu et al., 2015) models suggested that the SCB initially collided with the NCB at their eastern ends i.e. the current Dabie Orogenic Belt in late Paleozoic, and progressed westwards to the eastern Qinling Orogenic Belt. The second is that continental collision is a lengthy process and generates multi-stage geological records. Therefore, it is necessary to select study locations and to determine specific stages of the continental collisional process.

Initial collision is defined as the first contact between two opposing continents immediately after the final subduction of oceanic crust (Hu et al., 2016; Rowley, 1996). This marks the starting point of continental collision as well as orogenesis, which describes the subsequent collisional uplift and lithospheric evolution. In the eastern Qinling-Orogenic Belt and its peripheral, the timing of initial collision between the NCB and the SCB has been poorly constrained. Sedimentary rocks can provide age constraints for the initial collision between the SCB and the NCB. After collision, detrital material from the NCB should have been transported to the northern edge of the SCB (Deng et al., 2019; Shao et al., 2016), which would allow the timing of initial collision to be dated. In addition, stratigraphic and subsidence changes on the SCB might also have been triggered by the initial SCB–NCB collision. In this study, we investigated the Zigui and Dangyang basins located on the central northern-SCB, which are northernmost exposures of Mesozoic foreland sediments in the SCB. We documented the sedimentology and tectonic subsidence history and investigated the detrital zircon geochronology of the Triassic strata to assess the timing of initial SCB–NCB collision in the eastern Qinlng Orogenic Belt.