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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Degassing behaviour of vesiculated basaltic magmas: an example from Ambrym volcano, Vanuatu Arc
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Degassing behaviour of vesiculated basaltic magmas: an example from Ambrym volcano, Vanuatu Arc

机译：泡状玄武岩浆的脱气行为：以安布林火山，瓦努阿图弧为例

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摘要

Ambrym is one of the most actively erupting basaltic volcanoes in the Vanuatu island arc. Scoria clasts collected from a fallout deposit in the inner terrace of its Benbow active crater were analyzed through series of synchrotron X-ray computed microtomographic experiments, as well as permeability measurements and simulations. Our goal was to reconstruct and visualize scoria textures in 3D and to quantify vesicularity, permeability, vesicle sizes and distributions in order to understand how gas moves in and out of Ambrym basaltic magma. We find that vesicle size distributions in the volume range between ~10~3 and 10~(10) μm~3 define two scoria classes. Vesicle size distributions in the low-to-moderately (0.44-0.67) vesicular samples can be fit by power laws with an exponent of 1 ± 0.2; distributions in the highly vesicular (0.86-0.88) samples can be fit by power laws with a higher exponent (1.4 to 1.7), as well as by exponential fits. Highly vesicular samples exhibit a very pronounced large vesicle, consisting of networks of smaller, interconnected vesicles, that is more than three orders of magnitude larger in volume than all other vesicles in each distribution. This type of vesicle is not found in the low-to-moderately vesicular samples. In addition, vesicle number density negatively correlates with vesicularity: less vesicular samples have the highest number density and vice versa, and contain far more numerous small-to-medium-sized vesicles than highly vesicular samples. Measured and calculated viscous (Darcian) permeabilities overlap in the range 10~(-13) and 10~(-9) m~2, with higher values in the more vesicular samples. We ascribe these differences in the textural and physical properties of the scoria clasts to their derivation from distinct magma portions in the conduit that were driven by convective overturn and underwent different vesiculation histories and gas transport dynamics. Comparing basaltic scoria clasts from Ambrym to those from mild explosive activity at Stromboli volcano (Italy) reveals that differences in their vesicle size distributions may result from the influence of different crystal contents and shapes on the vesiculation and permeability of the respective magmas. Finally, we highlight how rheological properties have a fundamental role in determining the degassing behaviour of basaltic magma at Ambrym and other volcanoes in general.
机译：安布林是瓦努阿图岛弧线上最活跃的玄武岩火山之一。通过一系列同步加速器X射线计算机显微断层照相术实验以及渗透率测量和模拟，分析了从Benbow活性火山口内阶台的沉降物中收集到的Scoria碎屑。我们的目标是在3D中重建和可视化氧化渣纹理，并量化水泡，渗透性，囊泡大小和分布，以了解气体如何运入和运出Ambrym玄武岩浆。我们发现在约10〜3和10〜（10）μm〜3之间的体积范围内的囊泡大小分布定义了两个氧化sco类。低至中度（0.44-0.67）囊泡样品中的囊泡大小分布可以通过幂定律拟合，指数为1±0.2。高囊泡（0.86-0.88）样本中的分布可以通过指数较高（1.4至1.7）的幂定律进行拟合，也可以通过指数拟合进行拟合。高囊泡样品表现出非常明显的大囊泡，由较小的相互连接的囊泡网络组成，其体积比每种分布中的所有其他囊泡大三个数量级。在低至中度囊泡样品中未发现这种囊泡。此外，囊泡数密度与囊泡度呈负相关：较少的囊泡样本具有最高的囊泡密度，反之亦然，并且与高度囊泡的样本相比，囊泡中小型囊泡的数量要多得多。测量和计算的粘滞（达西人）渗透率在10〜（-13）和10〜（-9）m〜2范围内重叠，在更多的水泡样品中，该值较高。我们将这些熔渣岩的质地和物理性质的差异归因于它们是由对流翻转驱动的导管中不同的岩浆部分所引起的，并经历了不同的囊泡历史和气体输送动力学。将来自安布林的玄武岩碎屑与来自斯特龙博利火山（意大利）的轻度爆炸活动的碎屑进行比较，发现它们的囊泡大小分布不同可能是由于不同晶体含量和形状对相应岩浆的囊泡和渗透率的影响所致。最后，我们重点介绍了流变特性如何在确定Ambrym和其他火山的玄武岩岩浆的脱气行为中发挥根本作用。

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