Ascent and emplacement dynamics of obsidian lavas inferred from microlite textures
Ascent and emplacement dynamics of obsidian lavas inferred from microlite textures
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从微晶石纹理推断黑曜石熔岩的上升和就位动态
DOI：
10.1007/s00445-015-0971-6
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发表时间：
2015
影响因子：
3.5
通讯作者：
Matthew Williams
中科院分区：
文献类型：
--
作者：
K. Befus;M. Manga;J. Gardner;Matthew Williams
为了评估喷发和侵位的体积不同的流纹岩熔岩，我们测量了从黄石火山口和两个从莫诺火山口，美国的9个熔岩样品中收集的微晶数密度和方向。微晶岩由铁钛氧化物±碱性长石±单斜辉石组成。数密度的范围从108.11 ± 0.03到109.45 ± 0.15 cm−3，与各个熔岩流到喷口的距离无关，并且在大体积和小体积熔岩之间非常相似。总之，这些观察结果表明，在侵位过程中，数量密度是不变的，并且管道中的上升速率在小圆顶和大熔岩流之间是相似的。在1-2 MPa hr−1的减压速率下，连续减压实验产生的显微结构最好地复制了天然结构。针状微晶在所有天然样品中具有优先取向。由于微晶片取向的标准偏差不会变得更好地与行进的距离对齐，我们得出结论，微晶片退出管道对齐，并且在陆上流动期间的应变不足以进一步对齐微晶片。近喷口样品中微晶倾向和倾伏的方向表明，管道中的变形方式以纯剪切为主。我们推测，塌陷的可渗透泡沫提供了一种机制，以同时允许微晶形成和对齐，以响应脱气和通过纯剪切变平的组合。
To assess the eruption and emplacement of volumetrically diverse rhyolite lavas, we measured microlite number densities and orientations from samples collected from nine lavas in Yellowstone Caldera and two from Mono Craters, USA. Microlite populations are composed of Fe-Ti oxides ± alkali feldspar ± clinopyroxene. Number densities range from 108.11 ± 0.03 to 109.45 ± 0.15 cm−3 and do not correlate with distance from the vent across individual flows and are remarkably similar between large- and small-volume lavas. Together, those observations suggest that number densities are unmodified during emplacement and that ascent rates in the conduit are similar between small domes and large lava flows. Microtextures produced by continuous decompression experiments best replicate natural textures at decompression rates of 1–2 MPa hr−1. Acicular microlites have a preferred orientation in all natural samples. Because the standard deviation of microlite orientation does not become better aligned with distance travelled, we conclude that microlites exit the conduit aligned and that strain during subaerial flow was insufficient to further align microlites. The orientations of microlite trend and plunge in near-vent samples indicate that pure shear was the dominant style of deformation in the conduit. We speculate that collapsing permeable foam(s) provides a mechanism to concurrently allow microlite formation and alignment in response to the combination of degassing and flattening by pure shear.
模拟蒙特塞拉特苏弗里埃尔山火山堤坝管道中振荡超压引起的地面变形
影响因子：
2.9
作者：
Hautmann S
通讯作者：
Hautmann S