A case for CO2-rich arc magmas
A case for CO2-rich arc magmas
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DOI：
10.1016/j.epsl.2009.12.013
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发表时间：
2010-02-20
影响因子：
5.3
通讯作者：
Witham, Fred
中科院分区：
文献类型：
--
作者：
Blundy, Jonathan;Cashman, Katharine V.;Witham, Fred
岩浆上升过程中的气体损失控制着火山系统的化学和物理演化。被困在火山斑晶中的熔体包裹体包含挥发性演化的快照，但众所周知，难以解释的常规脱气模型，因为气体通量，扩散再平衡和外部来源也可以有助于挥发性预算。在这里，我们补充公布的熔融包裹体挥发性数据，从广泛的火山与新的离子微探针数据H2O，CO2，Be，B，Li和Sc的熔融包裹体从1980-1986年爆发的圣海伦火山。新的和已发表的数据表明，套件的熔体包裹体通常被取代，以更高的CO2含量比将从计算的开放或定量系统脱气趋势预测。我们调和所有的CO2-H2O数据到一个连贯的框架的基础上，在喷发过程中的气体熔融的比例。浅部储存的岩浆与从岩浆系统更深处释放的蒸汽的相互作用将熔体置换为富含CO2的成分。我们的观察要求，弧岩浆是显着更丰富的CO2比单独从熔体包裹体估计，因为在岩浆上升过程中捕获高CO2熔体的可能性低。我们通过钠长石-H2O-CO2模型系统的计算来说明这一过程。(C)2009爱思唯尔有限公司版权所有。
Gas loss from ascending magma controls the chemical and physical evolution of volcanic systems. Melt inclusions trapped in volcanic phenocrysts contain snapshots of volatile evolution, but are notoriously hard to interpret in terms of conventional degassing models because gas fluxing, diffusive re-equilibration and external sources can also contribute to the volatile budget. Here we supplement published melt inclusion volatile data from a wide range of volcanoes with new ion-microprobe data on H2O, CO2, Be, B, Li and Sc in melt inclusions from the 1980-1986 eruptions of Mount St. Helens. The new and published data demonstrate that suites of melt inclusions are typically displaced to higher CO2 contents than would be predicted from calculated open or dosed-system degassing trends. We reconcile all CO2-H2O data into a coherent framework based on the ratio of gas to melt during eruption. Interaction of shallow-stored magmas with vapours released from deeper in the magma system displaces melts to CO2-rich compositions. Our observations require that arc magmas are significantly more CO2-rich than is estimated from melt inclusions alone because of the low probability of trapping high CO2 melts during magma ascent. We illustrate this process with calculations in the model system albite-H2O-CO2. (C) 2009 Elsevier B.V. All rights reserved.