Experimental Investigation of Chemical Zoning in Olivine: Applications to Hawaiian Basalt

玄武岩喷发是地球上体积最大的火山活动类型。在基拉韦厄火山（美国夏威夷岛），涉及玄武岩岩浆的喷发在过去的三个世纪里造成了社会危害，包括重大的人员损失和对基础设施的破坏。最近人们发现，基拉韦厄火山并不像人们所认为的那样，是通过几十年以岩浆流为主的喷发活动而获得的温和名声，它实际上经历了每次持续几个世纪的喷发和喷发活动循环。火山下岩浆储层的状态、大小以及从地壳和地幔获得补给的频率，是决定在某一时期是否爆发或喷涌活动占主导地位的主要因素。在基拉韦厄火山和其他喷发玄武岩的火山中，橄榄石是最常见的矿物相。橄榄石作为揭示岩浆地下历史的代用品的潜力怎么强调都不为过：橄榄石是岩石学家用来研究喷发前岩浆过程发生时间的重要信息囊。该项目侧重于将矿物橄榄石作为鉴定工具，以表征岩浆系统和K&amp；#299；lauea等火山下岩浆补给的速度。实验室实验和对精选的20世纪基拉韦厄火山喷发产物中橄榄石化学的详细研究将为确定喷发周期的转变提供关键的约束。岩浆补给、混合和上升的历史以“化学带”的形式保存在橄榄石中，这是晶体形成元素的非随机空间变化。然而，阅读和解释橄榄石的化学分区可能会很复杂，因为不同的过程可能会相互重叠。橄榄石中的初级化学分带可以在熔体的初始生长过程中获得，但随着时间的推移，这种分带会随着晶格内元素的扩散而趋于平滑。这种扩散涂抹的程度越来越多地用于回溯喷发发生前岩浆混合和上升的时间。这些现代岩石学应用还有待于彻底的实验验证。通过一系列精心策划的实验室实验，该项目专注于破译橄榄石在玄武岩熔体中诞生和生长过程中获得一整套元素的化学分区的机制，以及这种分区被修改的速度。玄武岩熔体将被冷却到不同的温度，并在最终条件下放置不同的持续时间，以诱导结晶并随着时间的推移跟踪扩散再平衡。为了将实验结果应用于自然系统，从20世纪K&amp；#299；lauea火山（夏威夷）的化学分区模式将被研究。选择K&amp；#299；作为研究橄榄石的实验室，劳埃亚是多方面的。在上个世纪，这座火山至少爆发了50次（其中一次自1983年以来一直在持续），现有的研究表明，自20世纪50年代以来，这座火山一直在经历岩浆供应的激增。研究这些喷发产物中橄榄石的分带模式，提取与喷发前岩浆注入和补给有关的关键时间尺度信息，对于建立对未来行为的知情预测至关重要。

Basaltic eruptions are the dominant type of volcanism on Earth by volume. At Kilauea Volcano (Island of Hawai'i, USA), eruptions involving basalt magma have caused societal harm over the last three centuries, including significant human loss and damage to infrastructure. It was recently discovered that far from the tame reputation that Kilauea gained through decades of effusive, lava-flow dominated activity, the volcano actually undergoes cycles of explosive and effusive activity lasting several centuries each. The state of magma reservoirs underneath the volcano, their size, and the frequency at which they receive recharge from the crust and mantle, are main factors in determining whether explosive or effusive activity dominates in any period of time. At Kilauea and in other volcanoes that erupt basalt, olivine is the most commonly occurring mineral phase. Its potential as proxies for unraveling the subterraneous history of magmas cannot be overstated: olivine is a major information capsule that petrologists examine to recover the timing of magmatic processes occurring prior to an eruption. This project focuses on the mineral olivine as a forensics tool to characterize magmatic systems and the tempo of magma recharge under volcanoes like Kīlauea. Laboratory experiments and detailed studies of olivine chemistry within the products from select 20th century Kilauea eruptions will provide critical constraints for identifying transitions in eruptive cycles. The history of magma recharge, mixing and ascent is preserved in olivine in the form of 'chemical zoning', non-random spatial variations in the crystal-forming elements. However, reading and interpreting chemical zoning in olivine can be complicated because different processes may overprint each other. Primary chemical zoning in olivine can be acquired during initial growth in a melt, but this zoning tends to smooth out through time by element diffusion within the crystal lattice. The extent of this diffusion smearing is increasingly used to backtrack the timing of magma mixing and ascent before an eruption occurs. These modern petrological applications have yet to be subject to thorough experimental verification. Using a suite of carefully planned laboratory experiments, this project therefore focuses on deciphering the mechanisms by which olivine acquires chemical zoning for a whole suite of elements during its birth and growth in a basalt melt, and how fast this zoning is modified. A basalt melt will be cooled to different temperatures and left for various durations at the final conditions to induce crystallization and track diffusive re-equilibration through time. To exploit and apply the experimental results to natural systems, olivine from the products of several 20th century eruptions from Kīlauea Volcano (Hawaii) will be investigated for their chemical zoning patterns. The reasons for choosing Kīlauea as a laboratory for olivine studies are manifold. There have been no less than 50 eruptions in the last century (one that is ongoing since 1983), and existing work suggest that the volcano has been undergoing a surge in magma supply since the 1950s. Examining the zoning patterns of olivine in those eruption products and extracting critical timescale information pertaining to pre-eruptive magma injection and recharge will be essential to establish informed projections about future behavior.