The 26·5 ka Oruanui Eruption, Taupo Volcano, New Zealand: Development, Characteristics and Evacuation of a Large Rhyolitic Magma Body
The 26·5 ka Oruanui Eruption, Taupo Volcano, New Zealand: Development, Characteristics and Evacuation of a Large Rhyolitic Magma Body
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新西兰陶波火山26·5 ka Oruanui喷发：大型流纹质岩浆体的发育、特征和疏散
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发表时间：
2006
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通讯作者：
Andrew N. Sutton
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作者：
C. Wilson;S. Blake;B. Charlier;Andrew N. Sutton
形成火山口的 26•5 ka Oruanui 喷发（新西兰陶波）喷发了约 530 km3 的岩浆，>99% 为流纹岩，<1% 为镁铁质。流纹岩的 SiO2 含量为 71•8 至 76•7% wt %，Rb 含量为 76 至 112 ppm，但主要成分为 74–76% wt % SiO2。每个地层水平的平均流纹岩成分在喷发序列中不会发生显着变化。氧化物地温、相平衡和挥发分含量表明岩浆储存温度为830–760°C，100–200MPa。大多数流纹岩成分变化可以通过约 28% 的晶体分异来解释，涉及斑晶和副相（斜长石、斜方辉石、角闪石、石英、磁铁矿、钛铁矿、磷灰石和锆石）。然而，某些元素浓度和 87Sr/86Sr 比率的分散以及非平衡晶体成分的存在意味着液体、斑晶和继承晶体的混合对于组装流纹岩的成分谱也很重要。镁铁质成分包括通过受污染的拉斑玄武岩的分馏和地壳污染形成的拉斑岩组（52•3–63•3 wt % SiO2）和通过原始橄榄石斜长石玄武岩与流纹岩和拉斑镁铁质混合形成的钙碱性组（56•7–60•5 wt % SiO2）。岩浆。这两个镁铁质族群均不同于其他具有可比 SiO2 含量的陶波火山区喷发物。 Oruanui 岩浆体喷发的发展和破坏发生在约 40 kyr 范围内，并且 Oruanui 成分尚未在剧烈的年轻活动中复制。奥鲁努伊流纹岩并不是在一个更原始的先驱的单一演化阶段形成的，而是通过陶波岩浆系统中寿命较长的多基因、多时代的硅质深成岩成分的快速复兴而形成的。
The caldera-forming 26•5 ka Oruanui eruption (Taupo, New Zealand) erupted ~530 km3 of magma, >99% rhyolitic, <1% mafic. The rhyolite varies from 71•8 to 76•7 wt % SiO2 and 76 to 112 ppm Rb but is dominantly 74–76 wt % SiO2. Average rhyolite compositions at each stratigraphic level do not change significantly through the eruption sequence. Oxide geothermometry, phase equilibria and volatile contents imply magma storage at 830–760°C, and 100–200 MPa. Most rhyolite compositional variations are explicable by ~28% crystal fractionation involving the phenocryst and accessory phases (plagioclase, orthopyroxene, hornblende, quartz, magnetite, ilmenite, apatite and zircon). However, scatter in some element concentrations and 87Sr/86Sr ratios, and the presence of non-equilibrium crystal compositions imply that mixing of liquids, phenocrysts and inherited crystals was also important in assembling the compositional spectrum of rhyolite. Mafic compositions comprise a tholeiitic group (52•3–63•3 wt % SiO2) formed by fractionation and crustal contamination of a contaminated tholeiitic basalt, and a calc-alkaline group (56•7–60•5 wt % SiO2) formed by mixing of a primitive olivine–plagioclase basalt with rhyolitic and tholeiitic mafic magmas. Both mafic groups are distinct from other Taupo Volcanic Zone eruptives of comparable SiO2 content. Development and destruction by eruption of the Oruanui magma body occurred within ~40 kyr and Oruanui compositions have not been replicated in vigorous younger activity. The Oruanui rhyolite did not form in a single stage of evolution from a more primitive forerunner but by rapid rejuvenation of a longer-lived polygenetic, multi-age ‘stockpile’ of silicic plutonic components in the Taupo magmatic system.