Mesozoic tectonic evolution of the Southeast China Block: New insights from basin analysis
Introduction
Located in the southern segment of East Asian continental margin, Southeast China Block (SECB in short) is characterized by numerous Mesozoic residual basins and granites, formation of which reflected an intracontinental tectonic evolution of the SECB. The residual basins and granitic intrusions constitute a distinctive basin-range landform, which has been called as the South China Mesozoic Basin and Range System (Gilder et al., 1991, Li, 2000). The Mesozoic basins are characterized by their relative small sizes, variable accumulation environments and a complex basin–granite relationship (Ren and Chen, 1989).
The Middle-Late Triassic uplifting event associated with an ultrahigh-high-pressure metamorphism in the Dabie belt, east-central China, influenced strongly the SECB (Faure et al., 1998, Gilder et al., 1999, Grimmer et al., 2003); in the Nanling region on the southern side of the Dabie belt, the consistent folding structures of pre-Middle Triassic layers, the large-scale granites dated at 240–205 Ma and the residual Late Triassic–Early Jurassic basins were widely developed (GDBGMR, 1988, Shu et al., 2004, Shu et al., 2007, Zhou et al., 2006), recording this event.
Abundant rhyolitic volcanic rocks and highly aluminous granitoids with the age from 145 Ma to 105 Ma are distributed across the coastal region of SE China (Jahn et al., 1990, Wang et al., 1990, Lapierre et al., 1997, Zhou and Li, 2000). These volcanic-intrusive series and coeval basins were generated by a regional extension (Shu et al., 2007). Zhou and Li, 2000, Zhou et al., 2006 used the model “Pacific plate subduction plus basaltic underplating” to interpret the geodynamics of the SE-China Late Mesozoic volcanic-intrusive complexes.
Previous researches have mainly focused on the granitoids of the SECB, few studies of basins were performed, and geological features of the Mesozoic basins are poorly known, leading to an inadequacy of geodynamic interpretation for the SECB. In last years, a regional geological investigation on various Mesozoic basins was carried out, detailed field observations enable us to compile a 1:1,500,000 geological map of basins of the SECB and to obtain new geological data. Analysis on basin features provides some new insights for understanding the Mesozoic tectonic evolution of the SECB.
Section snippets
Geological background
Four regional-scale fault zones are distributed across the Mesozoic basin–granite region of the SECB. They are the sub-E–W-trending Shaoxing–Jiangshan–Pingxiang fault zone (SJPZ), the NE-trending Zhenghe–Dapu fault zone (ZDZ), the sub-N–S-trending Ganjiang fault zone (GZ), and the NE-trending Changle-Nanao zone (CNZ) (Fig. 1). Detailed tectonic characteristics of these fault zones have been described by many authors (Charvet et al., 1994, Gilder et al., 1996, Shu and Charvet, 1996, Shu et al.,
Strata of the basement
In the studied areas, the Precambrian is made up of mid-high metamorphic rocks such as mica-schist, gneiss, orthogneiss, phyllitized muddy-sandy flysch and siliceous rocks, which contain basalt, spilite, keratophyre and volcaniclastic intercalations dated at 800–1000 Ma (Li et al., 1996, Shu and Charvet, 1996, Shu et al., 2006, Zhou et al., 2002, Wang et al., 2006, Shu et al., 2008a, Shu et al., 2008b). Recent chronological results suggest that some of these rocks were formed during the Middle
The Wuyi orogen: a paleo-geographic separating unit during the Late Mesozoic
Our studies on petrotectonic assemblages, sedimentary structures and rocks indicating paleo-environment suggest that the Wuyi orogen was a separating unit in term of paleo-geography during the Late Mesozoic. Accumulating thickness reflects that the difference of sedimentary environment had taken place in this unit since the Middle Jurassic (Wang and Yang, 2007). The residual thickness of Middle Jurassic sequence was gradually thinned from southeast to northwest, that is, the 2000 m-thick
Correlation between basin and granite
The above-mentioned geological facts allow us to recognize the temporal-spatial correlation between basin and granite. Firstly, a Mesozoic basin formed usually somewhat posterior to its bordering granite, that is, the erosion of which provided fragments for the deposition of basin; this is confirmed by rich granitic detritus in the conglomerate and coarse sandstone. Secondly, the Mesozoic granitoids should be formed originally at deep-seated level and the coeval basins were built at
Concluding remarks
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The Late Triassic-Paleogene basins in the SECB, after the Indosinian tectonic event, might be divided into two types, namely a post-orogenic basin (Type I) and an intracontinental extensional basin (Type II). The formation of these basins connects with the evolution of geotectonics of the SECB. The post-orogenic basin was formed in the areas from the piedmont to the intraland during the Late Triassic to Early Jurassic; and the formation of the intracontinental extensional basin connects with an
Acknowledgements
Two reviewers, Charvet J. and Gilder S.A. are gratefully acknowledged for their valuable comments that improved the manuscript. We are grateful to Faure M. and Xu B. for their constructive suggestions. Dr. Marjan Onrust, Dr. Davis H. and Dr. Yin Hongwei are thanked for their thorough checking-revising of this manuscript for English grammar. This study is supported by grants from the National Natural Science Foundation of China (Grant Nos. 40634022, 40221301, 40132010 and 40572118) any by US
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