Abstract
Multiple tectonic events since the Neoproterozoic era have framed the present-day lithosphere in the Fujian province affiliated with the eastern part of the South China Block. Comprehensive information of the crustal structure and bulk properties can aid to understand the geological features and tectonic processes of still much debate in this region. An attempt is made in this study to explore crustal thickness and internal velocities across Fujian using the teleseismic receiver functions (RFs). The H-V stacking of joint P and S RFs improves to simultaneously estimate crustal thickness, average Vp and Vs, and derived Vp/Vs ratio and bulk sound speed in three backazimuth sectors for each of 17 stations. Furthermore, a Neighborhood Algorithm nonlinear inversion of P RFs is employed to determine the layered structures of Vs and Vp/Vs beneath all the stations. Results indicate the crustal thickness varies from at most ∼35 km in northwest Fujian to 30–35 km in the inland mountains and 27–30 km in the southeastern coasts. The inferred Moho geometry is nonplanar or inclined across the Zhenghe-Dapu (ZD) and Changle-Zhaoan (CZ) fault zones, especially in the southern ZD fault area. The average Vp/Vs suggests that the crust is predominantly felsic in the Wuyi-Yunkai orogen and intermediate-to-mafic in the Cretaceous magmatic and metamorphic zones. A high-velocity upper crust along the coastline is revealed, which attributes to the Pingtan-Dongshan metamorphic belt. At the sites near the ZD fault zone, the intracrustal negative discontinuity occurs at a shallower depth of ∼15 km marking an abrupt Vs decrease into the low-velocity mid-to-lower crustal layer, probably linked to the closed paleo-rift basin remnants. The lower crust across the Fujian is generally characterized by relatively lower Vs and higher Vp/Vs (1.80–1.84) consistent with those of the mafic-ultramafic rocks, which do not support the proposed extensive magmatic underplating in the Late Mesozoic.
Highlights
The Fujian province on the southeastern coast of China resides on the Cathaysia Block, the southeast part of the South China Craton formed by collision with the Yangtze Block in the northwest during the Neoproterozoic era (Figure 1A)
In western Fujian affiliated with the early Paleozoic Wuyi-Yunkai orogenic belt in South China, the crust has the thickness of 30–35 km and the backazimuthal difference in the Moho depth over 4 km is obtained for station YDFS in the southern ZD
The crustal velocities estimated in the three different quadrants are contrasting as well, indicating the possibly distorted or disrupted Moho interface and substantial velocity contrast across the fault zone
Summary
The Fujian province on the southeastern coast of China resides on the Cathaysia Block, the southeast part of the South China Craton formed by collision with the Yangtze Block in the northwest during the Neoproterozoic era (Figure 1A). The tectonic environment had changed from intraplate compressional to extensional stress regime in the Mesozoic (Li and Li, 2007) and been under extension again in the Cenozoic (Qiu et al, 2018). These tectonic events had led to the formation of numerous uplifted and depressed blocks separated by the NE-SW and NW-SE oriented faults or sutures (Wang et al, 1993; Figure 1A), among which the major ones are the NNE-NE trending Shaowu-Heyuan (SH), ZhengheDapu (ZD), Changle-Zhaoan (CZ) fault zones, and offshore Fujian littoral (FL) fault. The FL fault marks the western boundary of the strongly rifted Cenozoic basins in the Eurasian continental margin that has been flexed down by the load of the Taiwan orogen to the east (Lin et al, 2003; Zhan et al, 2004)
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