Formation of the mid-fifteenth century Kuwae caldera (Vanuatu) by an initial hydroclastic and subsequent ignimbritic eruption
Formation of the mid-fifteenth century Kuwae caldera (Vanuatu) by an initial hydroclastic and subsequent ignimbritic eruption
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十五世纪中叶的库瓦埃火山口（瓦努阿图）由最初的水碎屑和随后的冰凝灰岩喷发形成
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发表时间：
1994
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影响因子：
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通讯作者：
J. Eissen
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作者：
C. Robin;M. Monzier;J. Eissen
在世纪中期，在新赫布里底群岛弧中部发生了过去10000年来最大的一次火山爆发，形成了一个巨大的破火山口（12 x6公里）。这次喷发是在前破火山口建筑群的玛珥晚期阶段之后发生的，这是一系列交替的水岩浆沉积物和空气降落火山砾层的原因。凝灰岩有关的破火山口形成（从破火山口壁的复合部分上的沉积物的120米），在两个主要的熔结凝灰岩阶段与两个额外的水岩浆事件。较低的水岩浆凝灰岩从precaldera玛珥阶段主要是玄武安山岩的组成，但碎屑显示的组成范围从48%到60%的SiO2。来自熔结熔结相的未焊接和焊接灰流沉积物以及相关的中上部水岩浆沉积物也显示出较宽的成分范围（60- 73%SiO2），但主要为英安岩。这种宽的组成范围被认为是由于晶体分馏。从一种喷发类型（岩浆水喷发）到另一种喷发类型（大量熔结凝灰岩喷发的岩浆喷发）的显著演化，或者发生在整个凝灰岩系列上，或者发生在每个熔结凝灰岩阶段的开始，是破火山口形成事件最令人印象深刻的特征。这强烈表明触发的主要喷发阶段的岩浆-水的相互作用。提出了破火山口形成的三步模型：（1）来自中央喷口的中度水浆（序列HD 1-4）和岩浆（沉降物）活动，可能需要数月或数年的时间，影响的区域略宽于现在的破火山口。在这个阶段结束时，强烈的地震活动和火山口地区外的分异岩浆的挤出发生：（2）不均匀的英安岩释放在一个水岩浆幕（HD 5）。紧接着是两个主要的火山碎屑流（PFD 1和2）。随着岩浆排出量的增加，该阶段初期岩浆-水的强烈相互作用迅速减弱。随后的破火山口塌陷可能开始于破火山口的东南部;（3）英安质焊接凝灰岩在第二个主要阶段（WFD 1-5）期间就位。在这一阶段的开始，岩浆-水的相互作用继续，产生典型的水岩浆矿床（HD 6）。破火山口的坍塌延伸到破火山口的北方部分。先前的C14年代和南极冰中爆发性火山活动的记录表明，这一事件的高潮阶段发生在公元1452年。
In the mid-fifteenth century, one of the largest eruptions of the last 10 000 years occurred in the Central New Hebrides arc, forming the Kuwae caldera (12x6 km). This eruption followed a late maar phase in the pre-caldera edifice, responsible for a series of alternating hydromagmatic deposits and airfall lapilli layers. Tuffs related to caldera formation (≈ 120 m of deposits on a composite section from the caldera wall) were emitted during two main ignimbritic phases associated with two additional hydromagmatic episodes. The lower hydromagmatic tuffs from the precaldera maar phase are mainly basaltic andesite in composition, but clasts show compositions ranging from 48 to 60% SiO2. The unwelded and welded ashflow deposits from the ignimbritic phases and the associated intermediate and upper hydromagmatic deposits also show a wide compositional range (60–73% SiO2), but are dominantly dacitic. This broad compositional range is thought to be due to crystal fractionation. The striking evolution from one eruptive style (hydromagmatic) to the other (magmatic with emission of a large volume of ignimbrites) which occurred either over the tuff series as a whole, or at the beginning of each ignimbritic phase, is the most impressive characteristic of the caldera-forming event. This strongly suggests triggering of the main eruptive phases by magma-water interaction. A three-step model of caldera formation is presented: (1) moderate hydromagmatic (sequences HD 1–4) and magmatic (fallout deposits) activity from a central vent, probably over a period of months or years, affected an area slightly wider than the present caldera. At the end of this stage, intense seismic activity and extrusion of differentiated magma outside the caldera area occurred; (2) unhomogenized dacite was released during a hydromagmatic episode (HD 5). This was immediately followed by two major pyroclastic flows (PFD 1 and 2). The vents spread and intense magma-water interaction at the beginning of this stage decreased rapidly as magma discharge increased. Subsequent collapse of the caldera probably commenced in the southeastern sector of the caldera; (3) dacitic welded tuffs were emplaced during a second main phase (WFD 1–5). At the beginning of this phase, magma-water interaction continued, producing typical hydromagmatic deposits (HD 6). Caldera collapse extended to the northern part of the caldera. Previous C14 dates and records of explosive volcanism in ice from the south Pole show that the climactic phase of this event occurred in 1452 A.D.