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.