三水盆地中渐新世火山记录的新建与南海扩张

The new volcanics record in Sanshui Basin and its relationship with the spreading of the South China Sea

三水盆地是南海北部邻区陆域唯一具有新生代火山活动记录的盆地,最晚一期火山喷发时间是38Ma,也是南海北部陆域已知的在南海扩张之前最晚的火山喷发年代。应用K-Ar同位素年代测定方法,首次发现三水盆地存在29.27±1.52Ma的玄武岩和28.25±1.14Ma的流纹岩,构造判别图解指示其产出环境是板内拉张,与盆地之前火山类型一致,为双峰式火山岩,玄武岩具有与洋岛玄武岩相似的地球化学特征,流纹岩具有与A型花岗岩相似的地球化学特征,且玄武岩与流纹岩均与其他地区地幔柱成因火山岩具有相似的地球化学特征。这一代表板内破裂的双峰式火山记录将南海北部陆缘的火山喷发活动从早先已知的古新世—中始新世延续至渐新世中期,众所周知,南海的开裂起始时间约在32Ma,对于南海扩张期间周边陆域是否存在相关联的火山活动及建立南海早期开裂模式具有重要意义。

Sanshui Basin is the only basin that has Cenozoic volcanic records in the northern adjacent land area of the South China Sea, and the age of the last volcanic eruption in this basin is 38 Ma. This age is also the last eruption age before the South China Sea spreading in its northern land. Based on the K-Ar isotope dating method, the basalts(29.27±1.52 Ma) and rhyolite(28.25 ± 1.14 Ma)were first found in Sanshui Basin. This bimodal volcanic rock that represents intraplate rifting tectonic setting postponed the volcanic records from Palaeocene-Middle Eocene to Mid-Oligocene. As we all know, the initial age of the South China Sea spreading is about 32 Ma. So, it has great significance to answer if there is the relationship between the South China Sea spreading and its surrounding land volcanic activity. Meanwhile, the findings have important significance for establishing early spreading evolution model of the South China Sea.