Hydrogen isotopic composition and volatile contents of quartz-hosted rhyolitic melt inclusions from the early Bishop Tuff

To explore whether hydrogen isotopes can identify the source and modification of water in a silicic magma reservoir, we analyzed D/H ratios and dissolved H2O content of quartz-hosted, rhyolitic glass inclusions from the early Bishop Tuff, a time-honored testing ground for innovative petrologic studies. The rhyolitic inclusions indicate the early Bishop reservoir had δD values ranging from -40 to -60‰ (VSMOW). The rhyolitic melt represents a distinct, largely homogenous isotopic reservoir. When compared to the global record of basaltic glass inclusions, the rhyolitic inclusions preserve an isotopic signature that is most similar to subduction-related mafic melts.

为探究氢同位素能否示踪富硅岩浆储库中水的来源与演化改造过程，我们对早期毕夏普凝灰岩（Bishop Tuff）——岩石学创新研究久负盛名的试验场——中石英内含的流纹质玻璃包裹体开展了氘氢比（D/H）与溶解水（H₂O）含量分析。流纹质玻璃包裹体的分析结果表明，早期毕夏普岩浆储库的δD值介于-40‰至-60‰（维也纳标准平均海水，Vienna Standard Mean Ocean Water，简称VSMOW）。该流纹质熔体代表一个独特且整体近乎均一的同位素储库。相较于全球玄武质玻璃包裹体的同位素记录，本次研究中的流纹质玻璃包裹体所保留的同位素指纹，与俯冲成因的镁铁质熔体最为相似。