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首页> 外文期刊>Bulletin of Volcanology: Journal of the International Association of Volcanology and Chemistry of the Earth s Interior >Shallow plumbing systems for small-volume basaltic volcanoes
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Shallow plumbing systems for small-volume basaltic volcanoes

机译：小体积玄武岩火山的浅水管系统

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摘要

Eruptive dynamics in basaltic volcanoes are controlled, in part, by the conduit geometry. However, uncertainties in conduit shape and dike-to-conduit transition geometry have limited our predictive capability for hazards assessments. We characterize the subvolcanic geometry of small-volume basaltic volcanoes (magmatic volatile-driven eruptions, 0.1 to 0.5 km(3)) based on a synthesis of field studies of five basaltic volcanoes exposed to varying degrees by erosion and exhibiting feeder dikes, conduits, and vent areas <= 250 m depth. Study areas include East Grants Ridge (New Mexico, USA), Basalt Ridge, East Basalt Ridge, Paiute Ridge, and Southeast Crater Flat (Nevada, USA). Basaltic feeder dikes 250 to 100 m deep have typical widths of 4-12 m, with smooth host-rock contacts (rhyolite tuff). At depths less than 100 m, heterogeneities in the host rock form preferential pathways for small dike splays and sills, resulting in a 30-m effective width at 50 m depth. The development of a complex conduit at depths less than 70 m is reflected in bifurcating dikes and brecciation and incorporation of the country rock. The overall zone of effect at depths less than 50 m is <= 110 m wide (220 m elongated along the feeder dike). Based on comparisons with theoretical conduit flow models, the width of the feeder dike at depths from 250 to 500 m is expected to range from 1 to 10 m and is expected to decrease to about 1-2 m at depths greater than 500 m. The flaring shape of the observed feeder systems is similar to results of theoretical modeling using lithostatic pressure-balanced flow conditions. Sizes of observed conduits differ from modeled dimensions by up to a factor of 10 in the shallow subsurface (< 50 m depth), but at depths greater than 100 m the difference is a factor of 2 to 4. This difference is primarily due to the fact that observed eroded conduits record the superimposed effects of multiple eruptive events, while theoretical model results define dimensions necessary for a single, steady eruption phase. The complex details of magma-host rock interactions observed at the study areas (contact welding, brecciation, bifurcating dikes and sills, and stoping) represent the mechanisms by which the lithostatic pressure-balanced geometry is attained. The similarity in the normalized shapes of theoretical and observed conduits demonstrates the appropriateness of the pressure-balanced modeling approach, consistent with the conclusions of Wilson and Head (J Geophys Res 86:2971-3001, 1981) for this type of volcano.
机译：玄武岩火山的喷发动力学部分受导管几何形状控制。但是，导管形状和堤坝至导管过渡几何形状的不确定性限制了我们进行危害评估的预测能力。我们根据对5个玄武岩火山的不同程度暴露在侵蚀下并展示支线堤坝，导管，通风口区域<= 250 m深度。研究领域包括东格兰特岭（美国新墨西哥州），玄武岩岭，东玄武岩岭，派伊特岭和东南火山口平原（美国内华达州）。玄武岩堤防深度为250至100 m，典型宽度为4-12 m，具有光滑的主岩接触（流纹凝灰岩）。在小于100 m的深度处，主体岩石中的非均质性为小堤防扩展和下陷形成了优先通道，从而在50 m深度处产生了30 m的有效宽度。深度小于70 m的复杂管道的发展反映在分叉的堤防，裂和乡村岩石的结合中。在小于50 m的深度处，整个作用区域的宽度小于等于110 m（沿给料堤延长220 m）。基于与理论导管流量模型的比较，进料堤的宽度在250至500 m的深度范围预计为1至10 m，在深度大于500 m的范围内预计减小至1-2 m。观察到的进料器系统的张开形状类似于使用岩石静压平衡流动条件的理论模型结果。在浅地下（<50 m深度），所观察到的导管尺寸与模型尺寸相差最多10倍，但在深度大于100 m时，相差2到4倍。观测到的侵蚀导管记录了多次喷发事件叠加效应的事实，而理论模型结果定义了单个稳定喷发阶段所需的尺度。在研究区域观察到的岩浆－岩浆相互作用的复杂细节（接触焊接，成岩，分岔堤坝和基岩以及停止作用）代表了达到岩石静压平衡几何的机理。理论和观察到的导管规范化形状的相似性证明了压力平衡建模方法的适当性，这与Wilson和Head（J Geophys Res 86：2971-3001，1981）的结论是一致的。

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