Figure 4. Model of the main crustal structure beneath the
profile. (a) The CCP imaging results with a Gaussian factor of 2.0. (b)
The main variation in the Moho depth and the interpreted mechanism from
the above CCP imaging results. The pink circles are the automatically
picked Pms arrivals. The dashed pink line indicates the intracrustal
discontinuity. The solid pink line represents the undulating Moho
discontinuity. The pink stars represent the local earthquakes downloaded
from the IRIS website
(http://ds.iris.edu/ds/nodes/dmc/data/types/events/).
5 Conclusions
The main findings from our research are derived from the aligning and
migration of teleseismic receiver functions. With the potential
discovery of hot upwelling materials along the crustal channel discerned
from CCP imaging (Fig 4), we hypothesize that the relatively high Vp/Vs
ratio and upwelling of hot materials beneath approximately 23°N may be
caused by the retreat of the subducted Pacific slab. Combined with
previous results, we deduce that the remnants of the amalgamation of the
West and East Cathaysia blocks can be indicated by the extension of the
Gaoyao–Huilai and Zhenghe–Dapu faults through the crustal area. In
addition, we establish a simple model for the collision between the East
and West Cathaysia blocks along the deep faults. As shown in Figure 5,
the amalgamation of these two blocks is constrained to the
Neoproterozoic (1000~920 Ma), after which an intraplate
orogeny may have dominated during the Paleozoic along the suture zone
between the West and East Cathaysia blocks (460–400 Ma) (Fig 5 a). In
the mid-Permian (~265 Ma), the Pacific plate started to
subduct beneath the Cathaysia block, and in the mid-Paleozoic, it may
have experienced a series of slab retreat, rollback and tearing
processes (Fig 5 b). From the Jurassic to the Cretaceous, the subducted
Pacific slab may have severely foundered, which would have been
accompanied by the upwelling of hot materials (Fig 5 c). Therefore, the
amalgamation of the East and West Cathaysia blocks together with the
upwelling of hot materials played an important role in the formation of
the crustal state beneath the deep Gaoyao–Huilai and Zhenghe–Dapu
faults.