Magma decompression rates during explosive eruptions of Kilauea volcano, Hawaii, recorded by melt embayments
Magma decompression rates during explosive eruptions of Kilauea volcano, Hawaii, recorded by melt embayments
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DOI：
10.1007/s00445-016-1064-x
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发表时间：
2016-10-01
影响因子：
3.5
通讯作者：
Swanson, Donald A.
中科院分区：
文献类型：
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作者：
Ferguson, David J.;Gonnermann, Helge M.;Swanson, Donald A.
在火山喷发期间，岩浆上升时的减压速率是一个重要但缺乏约束的参数，它控制着许多影响喷发行为的过程。在这项研究中，我们量化了夏威夷基拉韦厄火山三次不同喷发的玄武岩岩浆的减压速率，方法是使用橄榄石承载的熔体管(海湾)中的挥发扩散。在喷发上升过程中，水、二氧化碳和S从海湾熔体中不完全地释放出来，形成了可以用微量分析技术测量的扩散剖面，然后对其进行建模，以推断平均减压速率。从夏威夷式喷泉到玄武岩浅成纪喷发，我们得到的平均喷发速率类似于0.050.45兆帕S(-1)，越强烈的喷发速率越高。这些岩浆的上升时间从大约5分钟到大约36分钟，从大约2公里到大约4公里不等。基于渗漏数据的减压-出溶模型还允许估计岩浆体内先前存在的出溶挥发分的质量分数。在所研究的喷发中，这从0.1wt%到3.2wt%不等，但似乎不是喷发强度的关键控制因素。我们的结果并不支持喷发前挥发物的浓度与喷发强度之间的直接联系；相反，他们表明，对于这些喷发，减压速率与质量排放速率的独立估计成正比。尽管喷发强度是由排放率定义的，但根据目前可用的海湾分析数据集，喷发强度似乎并不与平均减压率成线性关系。这项研究证明了间隔法在玄武岩喷发期间对岩浆上升提供定量约束的有效性。
The decompression rate of magma as it ascends during volcanic eruptions is an important but poorly constrained parameter that controls many of the processes that influence eruptive behavior. In this study, we quantify decompression rates for basaltic magmas using volatile diffusion in olivine-hosted melt tubes (embayments) for three contrasting eruptions of Kilauea volcano, Hawaii. Incomplete exsolution of H2O, CO2, and S from the embayment melts during eruptive ascent creates diffusion profiles that can be measured using microanalytical techniques, and then modeled to infer the average decompression rate. We obtain average rates of similar to 0.05-0.45 MPa s(-1) for eruptions ranging from Hawaiian style fountains to basaltic subplinian, with the more intense eruptions having higher rates. The ascent timescales for these magmas vary from around similar to 5 to similar to 36 min from depths of similar to 2 to similar to 4 km, respectively. Decompression-exsolution models based on the embayment data also allow for an estimate of the mass fraction of pre-existing exsolved volatiles within the magma body. In the eruptions studied, this varies from 0.1 to 3.2 wt% but does not appear to be the key control on eruptive intensity. Our results do not support a direct link between the concentration of pre-eruptive volatiles and eruptive intensity; rather, they suggest that for these eruptions, decompression rates are proportional to independent estimates of mass discharge rate. Although the intensity of eruptions is defined by the discharge rate, based on the currently available dataset of embayment analyses, it does not appear to scale linearly with average decompression rate. This study demonstrates the utility of the embayment method for providing quantitative constraints on magma ascent during explosive basaltic eruptions.