Chemistry of particles from the Toba ash layer

Two cores from the southern South China Sea contain discrete ash layers that mainly consist of rhyolithic glass shards. On the basis of the SPECMAP time scale, the ash layers were dated to ca. 74 ka, the age of the youngest Toba eruption in northern Sumatra. This link is supported by the chemical composition of the glass, which is distinct from volcanic glass supplied from the Philippines and the northern South China Sea, but is almost identical with the chemistry of the Toba ash. The youngest Toba ash layers in the South China Sea expand the previously known ash-fall zone over more than 1800 km to the east. The dispersal of ashes from Sumatra in both western and eastern directions indicates two contrasting wind directions and suggests that (1) the Toba eruption probably happened during the Southeast Asian summer monsoon season, and (2) the volume of erupted magma was larger than previously interpreted.南海南部的两根岩芯中发育离散分布的火山灰层，其主要组分为流纹质玻璃碎屑。基于SPECMAP时间标尺（SPECMAP time scale），这些火山灰层的定年结果约为74 ka，对应苏门答腊北部多巴（Toba）最近一次喷发的年代。该关联得到了玻璃化学成分的佐证：其化学成分与菲律宾及南海北部产出的火山玻璃截然不同，但与多巴火山灰的化学成分几乎完全一致。南海范围内发现的最新多巴火山灰层，将此前已知的火山灰沉降区向东扩展了超过1800千米。苏门答腊火山灰向西、向东双向扩散的特征，指示了两种相反的风向，由此可推导出两点结论：其一，多巴喷发事件大概率发生在东南亚夏季风时段；其二，此次喷发的岩浆体量大于此前的估算值。