The Sanshui Basin (SSB), a continental rift basin located at the southern continental margin of the South China Block, is characterized by widely distributed bimodal volcanic rocks. However, the petrogenesis of the bimodal volcanic rocks, particularly the predominantly exposed felsic volcanic rocks, is poorly constrained. This combined study of the petrology, geochronology and geochemistry of trachytes and rhyolites from the SSB aimed to constrain their petrogenesis and geodynamic implications. The mineral assemblages and geochemistry revealed the peralkaline affinity in the trachyte and rhyolite, and they were reclassified them as peralkaline felsic volcanic rocks. The zircon U-Pb LA-ICP-MS geochronology indicated a volcanism peak period in the Eocene (approximately 56 Ma). The peralkaline felsic rocks in the SSB were geochemically equivalent to A₁-type rhyolite, with high contents of Zr, Hf, and Nb and depleted Sr and Ba. Geochemical modeling results indicated that peralkaline felsic volcanic rocks were formed by parental basalt via protracted fractional crystallization with minor crustal contamination. We suggest that the Eocene peralkaline volcanic rocks formed in a passive continental rift setting because of the upwelling of the asthenospheric mantle, triggered by the far-field effect of the combined action of the Paleo-Pacific and the Neo-Tethys plates. The peralkaline volcanic rocks from the SSB recorded a Cretaceous extension transferred to a lithospheric rupture during the Early Cenozoic and present crucial insights into the Cenozoic breakup of the continental margin of South China.

三水盆地（SSB）是位于华南地块南缘的陆相裂谷盆地，具有广泛分布的双峰式火山岩特征。然而，双峰火山岩的成岩作用，特别是主要暴露的长英质火山岩，受到的限制很少。这项对来自 SSB 的粗面岩和流纹岩的岩石学、地质年代学和地球化学的综合研究旨在限制它们的岩石成因和地球动力学意义。矿物组合和地球化学揭示了粗面岩和流纹岩中的过碱性亲和性，并将它们重新分类为过碱性长英质火山岩。锆石 U-Pb LA-ICP-MS 年代学表明始新世（约 56 Ma）存在火山活动高峰期。SSB 中的过碱性长英质岩石在地球化学上等同于 A₁型流纹岩，Zr、Hf、Nb 含量高，Sr、Ba 贫化。地球化学模拟结果表明，过碱性长英质火山岩是由母体玄武岩经过长时间的分离结晶形成的，具有轻微的地壳污染。我们认为始新世过碱性火山岩是在被动大陆裂谷环境中形成的，这是由于古太平洋和新特提斯板块共同作用的远场效应引发的软流圈地幔上涌所致。来自 SSB 的过碱性火山岩记录了早新生代期间白垩纪伸展到岩石圈破裂的过程，并为了解华南大陆边缘新生代破裂提供了重要见解。