科研之友
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摘要
Situated in the southwestern segment of Qinzhou-Hangzhou joint belt, Bancheng area of southern Guangxi is a pivotal area in understanding the geological tectonic evolution history of South China since the Paleozoic. Late Devonian to late Permian siliceous rock sequences are outcropped in this area. In recent years, the authors conducted systematic field geological survey and found that there exist a series of siltstone intercalations in late Paleozoic siliceous rock sequences of the Shiti reservoir in Bancheng Town, Qinzhou City. In this paper, LA?MC?ICP?MS U?Pb isotopic dating was performed for detrital zircons from two siltstone intercalation samples of the lower and upper late Paleozoic siliceous rock sequences. Detrital zircon U?Pb age spectra shows that there are four main age groups of 407?573 Ma (early Paleozoic), 644?954 Ma (Neoproterozoic), 1124?1636 Ma (Mesoproterozoic) and 2368?2548 Ma (Early Paleoproterozoic-late Neoarchean), which recorded four major tectonic thermal events in this area. These four periods of tectonic thermal events are consistent with the ages of widely developed magmatic rocks in Yunkai area of the Cathaysia Block, indicating that Yunkai area might have been major depositional provenance for the siltstone intercalations of late Paleozoic siliceous rock sequences. The depositional provenances of the lower and upper late Paleozoic siliceous rock sequences are significantly different, and there is a general tendency toward increasing complex and relatively older age of detrital zircon from the lower to the upper of late Paleozoic siliceous rock sequences, indicating that the Yunkai Block has experienced rapidly erosion and uplift process after Caledonian orogeny in the southwestern segment of Qinzhou?Hangzhou joint belt. Detrital zircon U?Pb age spectra of the sandstone intercalations of late Paleozoic siliceous rock sequences imply that the Qinzhou-Fangchang Basin was in an extension tectonic setting in Late Paleozoic period.
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