Ni Systematics in Olivine as Fingerprints of Magmatic Processes in Hawaiian Basalts

矿物橄榄石是了解上地幔和地壳过程的基础重要性。橄榄石中的镍（Ni）含量非常重要，因为它是温度、压力、氧逸度和体相组成的敏感指标。通过大量的实验研究，在广泛的实验条件和组合物的镍在橄榄石中的平衡分配的影响因素进行了探讨。然而，镍和其他二价离子在橄榄石中的行为仍然知之甚少，因为在岩浆系统中的复杂过程。洋岛玄武岩，如那些来自夏威夷，橄榄石镍含量的变化很大。有许多相互竞争的假设来解释观测到的大范围变化。为了评估这些假设，将使用正在喷发的基拉韦厄火山的熔岩。这些熔岩也包含了广泛的镍，并具有良好的特点岩浆历史。分析已知岩浆历史的岩石中含镍相的主元素和微量元素，以评估每个岩浆过程在控制橄榄石中镍的相对重要性。 幔源岩浆的早期结晶历史以橄榄石为主。通常，它是原始夏威夷玄武岩中在低到中等压力下在液相线以下100 oC结晶的唯一矿物。橄榄石的成分已被广泛用于评价各种岩浆作用，包括结晶历史、岩浆混合聚集和混染作用。橄榄石中的镍含量因其与幔源熔岩的相容性强而引起人们的极大兴趣，并被认为在解释核的形成、地幔的性质和演化、地幔中的熔体形成以及玄武岩浆中的晶体分馏和聚集等方面具有重要意义。因此，橄榄石中的镍含量为地球过程提供了有价值的观点。像那些从夏威夷羽状熔岩显示高丰度，但在相同的MgO镍含量的变化很大。围绕着这种变异的起源存在争议。将使用表征良好的样品来评估哪些岩浆过程负责控制夏威夷玄武岩中橄榄石中的镍丰度。该项目的重点是基拉韦厄火山持续喷发的拉斑玄武岩和卡拉岛火山活动复兴阶段的碱性熔岩。基拉韦厄火山喷发的岩浆过程是众所周知的，包括岩浆混合，晶体积累和随时间变化的母岩浆成分。对于再生阶段的熔岩，其起源深度将使用橄榄石中的Ni进行研究。目前的深度估计是高度可变的。以前没有对再生熔岩中的橄榄石进行过高精度分析。这一研究对认识幔源玄武岩的源区岩性和形成条件具有重要意义。

The mineral olivine is of fundamental importance in understanding upper mantle and crustal processes. The nickel (Ni) content of olivine is of great interest because it is a sensitive indicator of temperature, pressure, oxygen fugacity and bulk composition. The factors that influence equilibrium partitioning of Ni in olivine have been explored through numerous experimental studies for a wide range of experimental conditions and compositions. However, the behavior in Ni and other divalent ions in olivine remains poorly known because of the complex processes in magmatic systems. Ocean island basalts, such as those from Hawaii, show large variations in olivine Ni content. There are many competing hypotheses to explain the wide range of observed variation. To evaluate these hypotheses, lavas from the ongoing eruption of Kilauea Volcano will be used. These lavas also contain a wide range in Ni and have well characterized magmatic histories. Analyzes of major and trace elements in Ni-bearing phases in rocks with known magmatic histories will be made to assess the relative importance of each magmatic process in controlling Ni in olivine. The early crystallization history of mantle-derived magmas is dominated by olivine. Usually, it is the only mineral to crystallize for 100 oC below the liquidus at low to moderate pressures in primitive Hawaiian basalts. The composition of olivine has been used extensively to evaluate various magmatic processes including crystallization history, magma mixing accumulation and contamination processes. The Ni content of olivine has been of keen interest because of its strong compatibility in mantle-derived lavas and has been considered of fundamental importance in interpreting core formation, the nature and evolution of the mantle, melt formation in the mantle, and crystal fractionation and accumulation in basaltic magmas. Thus, the Ni content in olivine provides valuable perspectives on Earth processes. Plume-related lavas like those from Hawaii show high abundances but wide variations in Ni content at the same MgO. Controversy surrounds the origin of this variation. Well characterized samples will be used to assess what magmatic processes are responsible for controlling Ni abundance in olivine from Hawaiian basalts. Tholeiitic basalts from the ongoing eruption of Kilauea Volcano and alkalic lavas from the rejuvenation stage of volcanism for Ka`ula Island are the focus of this project. Magmatic processes for the Kilauea eruption are well known including magma mixing, crystal accumulation and temporally varying parental magma composition. For the rejuvenation stage lavas, their depth of origin will be investigated using Ni in olivine. Current depth estimates are highly variable. No previous high precision analyzes have been done on olivine in rejuvenated lavas. This study will have implication for our understanding of the source lithology and formation conditions for mantle-derived basalts.