中国科学院南京地质古生物研究所机构知识库

Highly correlated with the Permian-Triassic Boundary (PTB) Mass Extinction in stratigraphy, volcanic ashes around the PTB in South China have been suggested to be a likely cause of the PTB Mass Extinction. So the nature, source and extent of the volcanic ashes are significant in figuring out the cause of the PTB Mass Extinction. In this study, we attempt to constrain the source and extent of the PTB volcanic ashes in South China by studying pyroclastic sedimentary rocks and the spatial distribution of tuffs and ashes in South China. The detrital zircons of tuffaceous sandstones from the Penglaitan section yield an age spectrum peaked at 252 Ma, with 80% of zircons U-Pb ages in 235 +/- 2.7 Ma similar to 258 +/- 4.8 Ma, 11% in 260 +/- 3.2 Ma similar to 276 +/- 3.6 Ma, six in 294 +/- 5.8 Ma similar to 561 +/- 6.9 Ma, five from Proterozoic, and the oldest age is 2063 +/- 13.4 Ma. The results of epsilon(Hf) (i) values varying from -16.5 similar to 5. 0, and Nb/Hf, Th/Nb and Hf/Th ratios of detrital zircons from the Penglaitan section are similar to those from arc/orogenic-related settings. Coarse tuffaceous sandstones (0. 5 similar to 2 mm) imply that their source is in limited distance. Those pyroclastic sedimentary rocks in Penglaitan are well correlated with the PTB volcanic ashes in Meishan GSSP section in stratigraphy. In the spatial distribution, pyroclastic sedimentary rocks and tuffs distribute only in southwest of South China, while finer volcanic ashes (< 0.3 mm) are mainly in the northern part. This spatial distribution suggests the source of tuffs and ashes was to the south or southwest of South China. Former studies, especially that of Permian-Triassic magmatism in Hainan Island and Early Mesozoic acid volcanic rocks in Southwest Guangxi have supported the existence of a continental arc related to the subduction and closure of Palaeo-Tethys on the southwestern margin of South China during Permian. It is suggested that the PTB ashes possibly derived from this Paleo-Tethys continental arc. The fact that contemporaneous volcanic ashes haven't been reported or found in North China or Northwest China implies a limited extent of the volcanism, which thus is too small to cause the PTB Mass Extinction.