Geochemistry at DSDP Legs 56-57 Holes@en

About 200 volcanic ash layers were recovered during DSDP Leg 57. The volcanic glass in some of these layers was investigated petrographically and chemically in this study. Volcanic glass is mainly rhyolitic and/or rhyodacitic in chemical composition, and its refractive index ranges from 1.496 to 1.529. Some volcanic ash layers consist of multiple grains of different chemical compositions. All the volcanic glass belongs to the tholeiitic and the calc-alkalic volcanic rock series, in SiO2-(Na2O + K2O) diagram and FeO*/MgO-SiO2 diagram. We correlated successfully three volcanic ash layers from the standpoint of chemical composition and biostratigraphy. Hydration of volcanic glass from Leg 57 is less intense than in other DSDP cores.本研究在深海钻探计划（Deep Sea Drilling Project, DSDP）第57航次中采集到约200层火山灰层。本研究对其中部分层位的火山玻璃开展了岩相学与地球化学分析。这些火山玻璃的化学成分以流纹质和/或英安流纹质为主，折射率介于1.496至1.529之间。部分火山灰层包含多种化学成分各异的颗粒。通过SiO₂-(Na₂O + K₂O)与FeO*/MgO-SiO₂成因判别图解分析，所有火山玻璃均归属于拉斑玄武岩系列与钙碱性火山岩系列。本研究基于化学成分与生物地层学特征，成功完成了3层火山灰的地层对比工作。第57航次采集的火山玻璃的水化程度弱于其他深海钻探计划岩芯。