Geochemical features and tectonic setting of the Late Cambrian volcanic rocks in Baoshan area of western Yunnan Province

The Late Cambrian volcanic rocks in Shangyanqing－Baiyan'aolinchang of Baoshan area within western Yunnan Province are poorly developed but distributed extensively. The volcanic rocks consist of early tholeiitic and alkali-basalt and late calc-alkali basalt. The geochemical characteristics of rocks show that early volcanic rocks formed in an extensional environment, whereas advanced volcanic rock was formed by subduction. The tectonic background of Baoshan terrane exhibited the transformation from extension to subduction in the late Cambrian, with the formation of the unconformity between Ordovician and Cambrian. This discovery provides petrological evidence for the conversion of the eastern part of the northern margin of Gondwana from passive continental margin to active continental margin.