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Predevonian Tectonic Evolution of South China: from Cathaysian Block to Caledonian Period Folded Orogenic Belt
- SHU Liang-shu
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2006, 12(4):
418-431.
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The interpretation of Predevonian tectonics of South China is controversial long time both on its age and distribution. Based on the middle-high grade metamorphic rocks, ductile slipping rheologic structures exposed in the the Zhejiang- Fujian-Jiangxi-Guangdong domain and high quality dating data published recently, the author believes that an ancient continental block existed certainly in South China, which is composed of Proterozoic schist, gneiss and migmatite with an oldest age of 2 Ga, their protolites are clastic rocks, volcanic rocks and plutons. This old land is temporarily called as Cathaysian Continental Block which is limited in the domain between Shaoxing-Jiangshan-Pingxiang fault and Zhenghe-Dapu fault, and its scope is less than that defined by Grabau. During 800-900 Ma, following the closure of paleo-South China ocean, Cathaysian block collided with Yangzi block and then became a part of Rodinia supercontinent. Not long time after converging, by affection of breakup of Rodinia supercontinent, proto-Cathaysian continental block was split into three sub-blocks, namely the southeastern Zhejiang-northwestern Fujian, the central-southern Jiangxi and the Yunkaidashan, and several rifts or sea channels occurred among them. From Early Sinian to Late Ordovician, these sea channels were expanded and were filled by 10000-20000 m thick clastic rocks (containing limestone) and turbidites. However coeval ophiolite and volcanic rocks are absent, implying extended fault did not reach to upper mantle. New geochronological results indicate that the ophiolite and volcanic rocks in the study areas, which were described as Early Paleozoic by previous researchers, yielded pre-Sinian ages, concentrating mainly between 800 Ma and 900 Ma. Thus, the previous Early Paleozoic tectonic framework needs to be re-constructed. In Silurian, a strong tectono-thermal event took place in South China, causing closure of Sinian-Early Paleozoic sea channels and folding-uplifting of mega-thick sediments. The South China Caledonian fold and orogenic belt was formed on the Proterozoic metamorphic basement. In the study area, folding deformation and ductile slipping rheology are very common, including thrust and strike-slip deformation, the peak period of deformation is 420-400 Ma. At the same time, a violent granitic magmatism was started, forming numerous strongly peraluminous S-type granites with A/CNK (molar Al2O3/[CaO + Na2O + K2O]) > 1.1, and I-type granitoids is rare. Peak period of granitic magmatism took place in the 430-400 Ma. Then, the whole South China Caledonian folded geological bodies were overlain unconformably by Late Devonian conglomerate and coarse sandstone, indicating termination of folding and orogeny. From Late Devonian, a united paleo-geographic and sedimentary environment occurred really in the study domain and its neighboring areas.
