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.