Plain Language Summary
In recent years, with the development of short-period dense array, people can detect many fine crustal structures, which is an important milestone in the development of seismology observations. Using a short-period dense seismic array deployed in the Cathaysia block, we obtained an unprecedented detailed profile from Zhuhai to Lianzhou City in Guangdong Province, China. Depending on this, we find that the abnormal deepen and offset Moho beneath the Sanshui basin may indicate the deep extension of the Gaoyao-Huilai deep fault. The occurrence of a 4.3Mw earthquake provides this interpretation with certain evidence. The new finding from our research provides good constrain for the remnants of amalgamation of the East and West cathaysian block in the southwest Chathaysia block, and which has not been reported before.
1 Introduction
1.1 Tectonic setting of the South China block
The South China block (SCB), located near the southeastern edge of the Eurasian plate, is believed to have been assembled following the Neoproterozoic collision between the Yangtze and Cathaysia blocks along the Jiangnan orogenic belt (Zhao & Cawood, 2012) (Fig 1 b). The Cathaysia block located in the southeastern SCB is broadly divided into the East and West Cathaysia blocks by the Gaoyao–Huilai and Zhenghe–Dapu faults. Three main tectonic events (the Jinningian event at ~970 Ma, the Caledonian event at ~420 Ma, and the Indosinian event at ~230 Ma) have been proposed based on outcrops of metamorphic rocks to account for the complex tectonic history of the SCB. Recently, researchers favored that the above events may have been driven mainly by the closure of the Paleo-South China Sea, Proto-Tethys and Paleo-Tethys Oceans, and Paleo-Pacific Ocean, respectively (Shu et al., 2021). In particular, the subduction of the Paleo-Pacific plate and cycle of slab advance and retreat, including the initiation of subduction, the occurrence of flat subduction, and slab rollback (Li & Li, 2007), played important roles in the widespread distribution of mid-late Mesozoic metamorphic and igneous rocks throughout the Cathaysia block (Jiang et al., 2015).
The well-known Jinningian event may represent the collision between the Yangtze and Cathaysia blocks, and characterized by a double subduction model along the Jiangshan Orogenic belt (Zhao, 2015) . In response to the amalgamation of the North China block with the SCB, the Caledonian tectonothermal event is indicated by granite gneissic rock (206Pb/238U apparent age of 421–441 Ma) in the Wuyi–Yunkai domain within the southeastern Cathaysia block (Wang et al., 2007). The Mesozoic granites formed by partial melting of the upper and middle crust may caused from the extensive Indosinian and Yanshanian metamorphic rocks in the Cathaysia block (weighted mean206Pb/238U age of ~236 Ma) Zhou (2003). Nevertheless, considering that S-type granites correlate with the melting of the middle or upper crust while I-type granites correlate with the melting of the lower crust (Tang et al., 2021), the petrogenesis of different types of granites in the Cathaysia block is still disputed. Specifically, some arguments focus on whether outcrops of metamorphic rocks are associated with an intraplate orogeny or subduction-collision processes. In this consuptions, Liu et al. (2018) support an oceanic subduction and accretion genesis hypothesis, whereas other groups support intraplate orogenesis (460–400 Ma) (Huang et al., 2013; Tang et al., 2021; Yu et al., 2018). However, without high-resolution data, there is no direct evidence supporting the amalgamation of the East and West Cathaysia blocks, especially in the southwestern portion of the Cathaysia block.