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首页> 外文期刊>Journal of Volcanology and Geothermal Research2012V243-244NOCT,15 >Dynamics and pre-eruptive conditions of catastrophic, ignimbrite-producing eruptions from the Yenkahe Caldera, Vanuatu
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Dynamics and pre-eruptive conditions of catastrophic, ignimbrite-producing eruptions from the Yenkahe Caldera, Vanuatu

机译：瓦努阿图Yenkahe破火山口的灾难性火山成因爆发的动力学和喷发前条件

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摘要

A combined stratigraphic and geochemical examination of similar to 43 kyr of volcanic activity is presented for the Yenkahe Caldera, a mafic-intermediate volcanic system on the island of Tanna, in the Vanuatu Arc. Through this period two catastrophic ignimbrite-producing eruptions have occurred: the Siwi eruption and the older, Old Tanna Ignimbrite eruption. The latter was previously linked with a different edifice to the north-east, however re-examination has shown it was derived from the Yenkahe Caldera. Radiocarbon dating of this ignimbrite gives an age of similar to 43 kyr B.P. Both eruptions produced voluminous ignimbrite sheets, however differences in deposit sequences show that the eruptions followed distinct courses. Deposits from the more recent Siwi eruption display greater evidence for phreatomagmatic phases during eruption onset. Both ignimbrites are distributed asymmetrically about the caldera, indicating partial collapse in each case. The early stages of the Siwi eruption produced directed pyroclastic surges and spatter fountains. Between these two major eruptions, volcanic activity was maintained through the formation of small, discrete volcanic cones, such as Yasur, which is active today. Whole rock major and trace element data show that intra-caldera activity between cataclysmic eruptions produced magmas of uniform basaltic-trachy-andesitic composition (SiO2 similar to 56 wt.%). Minerals within these lavas appear to be in equilibrium with their host. The Siwi eruption produced the most evolved, trachy-andesitic magma (SiO2 > 58 wt.), while the Old Tanna eruption is associated with less evolved, basaltic-andesite magma (SiO2 similar to 53 wt.%). Juvenile clasts from both ignimbrites display diverse mineral chemistry and mineral disequilibrium textures. From these variations in geochemistry and petrology we suggest that a crystal mush or resident magma remained following low-magnitude, intra-caldera activity. MELTS modelling suggest that this was stored at shallow depths, equivalent to pressures <1 kbar. Injection and mingling/mixing with primitive magma rejuvenated this mush component to trigger the ignimbrite eruptions. (C) 2015 Elsevier B.V. All rights reserved.
机译：针对瓦努阿图弧线塔那岛上的镁铁质中级火山岩系统Yenkahe Caldera，进行了大约43年火山活动的地层和地球化学综合检查。在此期间，发生了两次灾难性的爆炸物爆发：锡威火山喷发和年长的老塔纳因火山岩喷发。后者以前与东北的另一座大厦相连，但是重新检查表明它是从Yenkahe Caldera派生的。这种火成岩的放射性碳测年表明其年龄类似于公元前43年。两次喷发均产生大量的火成岩片，但是沉积顺序的差异表明喷发遵循不同的过程。来自最近的西维人喷发的沉积物显示出在喷发开始时发生岩浆相的更多证据。两种火成岩均围绕火山口不对称分布，表明在每种情况下均部分塌陷。锡威火山喷发的早期产生了定向的火山碎屑潮和飞溅的喷泉。在这两次主要喷发之间，通过形成小的离散的火山锥（例如Yasur）维持了火山活动，而Yasur如今仍在活动。整个岩石的主要和微量元素数据表明，大爆发之间的火山口内活动产生了均匀的玄武质-长安山-安山岩成分（SiO2接近56 wt。％）的岩浆。这些熔岩中的矿物质似乎与其基质保持平衡。锡威火山喷发产生的是演化最多的曲安山岩岩浆（SiO2> 58 wt。），而旧塔纳火山喷发与演化较少的玄武岩-安山岩岩浆（SiO2约占53 wt。％）有关。两种火成岩的幼岩都表现出不同的矿物化学和矿物不平衡质地。从地球化学和岩石学的这些变化中，我们建议在低强度的破火山口内部活动后仍会保留晶体糊状物或岩浆。 MELTS模型表明，该材料存储在浅深度，等于<1 kbar的压力。注入和与原始岩浆混合/混合可使该糊状成分恢复活力，从而触发火成岩喷发。 （C）2015 Elsevier B.V.保留所有权利。

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