Figure 3. (a) Stacking profile of all the receiver functions
after the Pms, PmpPms, PmpSms moveout corrections with a Gaussian factor
of 5.0. The solid black line indicates the error during the stacking in
each interval, and it is calculated by using the standard deviation with
100 resamplings based on the 1-D bootstrap method. (b) The top panel
shows the topographic relief along the profile. The middle two panels
are the number of stacked receiver functions and the arrival times of
the Pms, PmpPms, and PmpSms phases. The bottom two panels present the
crustal thickness and Vp/Vs ratio calculated by the H–k method. The
error is indicated by the differences calculated by the H–k method
using the arrival times after the Pms and PmpPms moveout corrections.
The original data is show in Supplementary materials (Tabel S1).
4 Dicussions
For the exploration of the gold mineralization beneath the Yuegui and
Yuezhong blocks, a shorter dense seismic array was oriented in nearly
the same direction to us but slightly biased to the west. From the
obtained 233 teleseismic receiver functions based on 112 portable EPS-2
short-period seismometers, Li et al. (2021) deducted that a slightly
uplifted Moho and the presence of a massive negative phase may be
correlated with magmatism and mineralization beneath the Luoding–Yunfu
nappe tectonic zone. After acquiring data from another 400 km long
wide-angle seismic profile based on six active sources and approximately
54 DZSS-1 seismographs, Zhang et al. (2013) suggested that the Moho east
of the Chenzhou–Linwu fault belt is obviously uplifted which can be
considered as the convergent boundary bwteen the Yangtz and Cathaysia
blocks, while the low P-wave velocity anomalies in this region that may
have been caused by an upwelling of hot asthenosphere.. More recently,
employing both active and passive dense seismic arrays with the same
starting point as our array (but a southernmost geophone situated more
toward the east), Deng et al. (2019) obtained more than 10,000 receiver
functions from 2010 to 2015. The most stable feature was a slightly
uplifted Moho towards the southeast in their stacking profile. Combined
with a velocity model inverted by using surface waves, they found
possible lithospheric thinning and the potential upwelling of hot
material beneath the centre of Guangdong Province. In another study
based on SinoProbe reflection profiling, Dong et al. (2020) found that
the structure of the Zhenghe–Dapu fault could be depicted with a stack
of parallel reflectors dipping 30° to the northwest. From the above
results, it appears that an abnormally weak suture zone may be
distributed along the coastal area of the Cathaysia block that is
spatially consistent both with the metamorphic core in the
Wuyi–Nanling–Yunkai domain distributed along the Zhenghe–Dapu and
Gaoyao–Huilai deep faults.
The uplift of the Moho to the
southeast in the coastal SCB may be connected to the passive continental
margin (Bai et al., 2015). Other evidence indicates that the
lithosphere-asthenosphere boundary (LAB) discontinuity also exhibits an
uplift trend from the continental margin of the SCB to the northern SCS,
and variation of Moho in our profile exhibits the same characteristics
as previous results (Tang & Zheng, 2013). In addition, the most obvious
feature in our results is the abnormal deepen of Moho beneath
23.5~22.5°N, which can be observed from the aligning
profile and CCP imaging with different Gaussian factors (Figs 2, S2, and
S3). Simultaneously, multiple converted waves in our results (PmpPms,
PmpSms) display a similar pattern as the Pms phase (Fig 3 a). The
relatively large Vp/Vs ratio (≥1.8) beneath the same area may indicate
the presence of melt within the crust (Christensen, 1996). The Pms phase
beneath 23.7°N shows an offset pattern, and we infer that it may be due
to the extension of the deep Gaoyao–Huilai fault, which is served as a
deep channel for the upwelling hot materials (Fig 4). Combined with a
velocity model (Zhou et al., 2012), it can be observed that hot
materials appear to accumulate beneath 23.5°N and 22.5°N (Fig S4). The
consistent trend of the negative phase above the deepen Moho supports
the upwelling of hot materials along the hot channel beneath
approximately 23.7°N (Fig 2 a). The occurrence of the Mw 4.2 earthquake
adjacent to this hot channel is evidence of the existence of such a hot
channel along the deep fault (Fig 4).
According to the previously reported zircon U–Pb ages of different
groups of granitic gneisses, Wang et al. (2014) proposed that the SCB
was formed by the amalgamation of various fragments following the
episodic closure of a series of northwestern arc-back systems along
Wuyi–Yunkai, Shuangxiwu and Jiangnan at ~920 Ma,
~890 Ma, and ~830 Ma, respectively. The
collision boundary between the East and West Cathaysia blocks may be an
extension of the Zhenghe-Dapu fault, which is connected to the
Gaoyao–Huilai fault to the southeast. Under these assumptions, a
previous study confirmed that parallel reflectors dipping 30° to the
northwest may represent an extension of the Zhenghe–Dapu fault (Dong et
al., 2020). From our results, we support the thickened crust beneath
around the Gaoyao-Huilai deep fault, while the relatively large Vp/Vs
ratio above the thickened crust may be caused by the upwelling of hot
materials. Furthermore, it should be mentioned that these hot materials
may have formed by the slab rollback of the subducted Paleo-Pacific
plate from the Late Cretaceous to late Cenozoic (Jiang et al., 2015);
another possibility is that it was formed by the lateral flow of hot
mantle from the Hainan plume (Zhang et al., 2020).
Taking the above considerations, we
present a simple model for the variation in the Moho depth beneath the
Gaoyao–Huilai and Zhenghe–Dapu faults that may represent the suture
zone between the amalgamated East and West Cathaysia blocks. Moreover,
the outcrops of metamorphic S-type granites indicate that the
amalgamation history is heterogeneous along the two deep faults. Given
the lower abundance of metamorphic rocks in the Wuyi–Nanling–Yunkai
domain, we deduce that the Nanling domain may be a buffer zone
(112–115°N) of the collision between the West and East Cathaysia
blocks, as depicted by the pink shading in Figure 1. The Yunkai and Wuyi
domains, which are depicted with red shading, may have formed through
lithospheric delamination process (Gao et al., 2004) and followed by an
intraplate orogeny, represent the severe collision zone of the East and
West Cathaysia blocks.