Timescales of mixing and storage for Keanakāko‘i Tephra magmas (1500–1820 C.E.), Kīlauea Volcano, Hawai‘i
Timescales of mixing and storage for Keanakāko‘i Tephra magmas (1500–1820 C.E.), Kīlauea Volcano, Hawai‘i
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夏威夷 Kälauea 火山 Keanakäkoäi Tephra 岩浆（公元 1500 年至 1820 年）混合和储存的时间尺度
DOI：
10.1007/s00410-017-1395-4
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发表时间：
2017
影响因子：
3.5
通讯作者：
Swanson, Donald A.
中科院分区：
文献类型：
--
作者：
Lynn, Kendra J.;Garcia, Michael O.;Shea, Thomas;Costa, Fidel;Swanson, Donald A.
在过去的2500年里，夏威夷的卡波劳亚火山的活动特点是，几个世纪以来，主要是热情洋溢或爆炸性的喷发。最近一段时期的爆发活动产生了Keanakakako 'i Tephra（KT;约。（公元1500-1820年）发生在山顶火山口坍塌之后（公元1470-1510年）。以前的研究表明，KT岩浆可能已经迅速上升到表面，绕过地壳水库的存储。储存条件和快速上升假设进行测试，在这里使用化学分区橄榄石晶体和热力学模型。镁橄榄石含量（Fo;[Mg/（Mg + Fe）× 100]）来识别克拉维海史前的熔体成分（即，1823年以前）的管道系统。原始（≥ Fo 88）岩心出现在整个300+年的KT期;它们起源于幔源岩浆，这些岩浆首先混合并储存在地壳深部储层中。双峰橄榄石群（≥ Fo 88和Fo 83 -84）记录了原始岩浆和系统中较浅的更有区别的储层组分的反复混合，产生混合成分（Fo 85 -87）。使用MELTS的相平衡模拟表明，液相线橄榄石在深度>17 km时不稳定。因此，计算的时间尺度可能记录了地壳内的混合和储存。铁镁和镍分区模式（正常，反向，复杂）的建模显示，KT岩浆混合和存储几个星期到几年前爆发，说明了一个更复杂的存储历史比直接和快速上升从地幔之前推断的KT岩浆。复杂分区的晶体在外部5-20 µm边缘也有平滑的成分反转，与周围的玻璃失去了Fe-Mg平衡。扩散模型表明，这些边缘形成在几个小时到几天内，这表明至少有一个额外的，后期混合事件可能发生在喷发前不久。我们的研究表明，KT岩浆的寿命比以前提出的更复杂，大多数KT岩浆并没有迅速上升，从地幔中没有修改在地壳浅部存储。
The last 2500 years of activity at Kīlauea Volcano (Hawai‘i) have been characterized by centuries-long periods dominated by either effusive or explosive eruptions. The most recent period of explosive activity produced the Keanakāko‘i Tephra (KT; ca. 1500–1820 C.E.) and occurred after the collapse of the summit caldera (1470–1510 C.E.). Previous studies suggest that KT magmas may have ascended rapidly to the surface, bypassing storage in crustal reservoirs. The storage conditions and rapid ascent hypothesis are tested here using chemical zoning in olivine crystals and thermodynamic modeling. Forsterite contents (Fo; [Mg/(Mg + Fe) × 100]) of olivine core and rim populations are used to identify melt components in Kīlauea’s prehistoric (i.e., pre-1823) plumbing system. Primitive (≥Fo88) cores occur throughout the 300+ years of the KT period; they originated from mantle-derived magmas that were first mixed and stored in a deep crustal reservoir. Bimodal olivine populations (≥Fo88and Fo83–84) record repeated mixing of primitive magmas and more differentiated reservoir components shallower in the system, producing a hybrid composition (Fo85–87). Phase equilibria modeling using MELTS shows that liquidus olivine is not stable at depths >17 km. Thus, calculated timescales likely record mixing and storage within the crust. Modeling of Fe–Mg and Ni zoning patterns (normal, reverse, complex) reveal that KT magmas were mixed and stored for a few weeks to several years before eruption, illustrating a more complex storage history than direct and rapid ascent from the mantle as previously inferred for KT magmas. Complexly zoned crystals also have smoothed compositional reversals in the outer 5–20 µm rims that are out of Fe–Mg equilibrium with surrounding glasses. Diffusion models suggest that these rims formed within a few hours to a few days, indicating that at least one additional, late-stage mixing event may have occurred shortly prior to eruption. Our study illustrates that the lifetimes of KT magmas are more complex than previously proposed, and that most KT magmas did not rise rapidly from the mantle without modification during shallow crustal storage.
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