Paleogeographic Implications of Early-Middle Permian Radiolarian-Bearing Sequences in the Changning-Menglian Belt (sw China) for Understanding the Evolution of the Paleo-Tethys

The Changning-Menglian belt in western Yunnan, China, preserves well-developed radiolarian-bearing sequences, providing key archives for investigating Paleo-Tethys evolution in this region. From the Early–Middle Permian siliceous-clastic rock sequences near the Nanpan village, this study identifies two radiolarian assemblages: an Early Permian fauna (including Pseudoalbaillella rhombothoracata, P. scalprataand P. postscalprata), and a Middle Permian fauna (represented by Follicucullusscholasticus, F. porrectus, F. dilatatus and F. ventricosus). These low-diversity assemblages resemble those of the Sibumasu block but differ markedly from the high-diversity assemblages of South China. Detrital zircons from interbedded sandstones are dominated by Pan-African (500–600 Ma) and Grenvillian (900–1200 Ma) age populations. The age difference between zircon crystallization and host strata deposition is consistent with a passive continental margin setting. The zircon age spectra closely match those of Gondwanan-affinity blocks, in clear contrast to the patterns characteristic of the South China and Simao (-Indochina) blocks. Integrated lithostratigraphic evidence from radiolarian fossils and detrital zircons unequivocally indicates a Gondwanan affinity for the Early–Middle Permian radiolarian-bearing sequences in the Nanpan area. The data imply deposition along the northern passive continental margin of a Gondwanan-related block, most likely adjacent to the Baoshan block. The distinct fossil and detrital zircon signatures, contrasting sharply with their counterparts in South China and Simao (-Indochina), point to a significant paleogeographic barrier―interpreted here as an extensive oceanic domain that isolated these blocks.