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

矿物橄榄石在认识上地幔和地壳过程中具有重要意义。橄榄石中的镍(Ni)含量是温度、压力、氧逸度和体积成分的敏感指标，因此引起了人们的极大兴趣。通过对各种实验条件和成分的大量实验研究，探索了影响镍在橄榄石中平衡分配的因素。然而，由于岩浆系统中复杂的过程，镍和其他二价离子在橄榄石中的行为仍然鲜为人知。大洋岛玄武岩，如来自夏威夷的玄武岩，显示出橄榄石镍含量的巨大差异。有许多相互竞争的假设来解释观察到的大范围变化。为了评估这些假设，将使用基拉韦厄火山正在喷发的熔岩。这些熔岩还含有广泛的镍，并具有很好的岩浆史特征。对已知岩浆史的岩石中含镍相的主量元素和微量元素进行分析，以评估每一次岩浆作用在控制橄榄石中镍的相对重要性。地幔岩浆早期结晶历史以橄榄石为主。通常，在原始夏威夷玄武岩中，它是唯一一种在低至中等压力下低于液相线100摄氏度结晶的矿物。橄榄石的成分已被广泛用于评价各种岩浆过程，包括结晶历史、岩浆混合堆积和混染过程。橄榄石的镍含量因其与地幔熔岩的强烈配伍性而引起人们的浓厚兴趣，并被认为对解释核形成、地幔的性质和演化、地幔中熔体的形成以及玄武岩岩浆中的晶体分馏和聚集具有重要意义。因此，橄榄石中的镍含量为研究地球过程提供了有价值的视角。与羽流有关的熔岩，如来自夏威夷的熔岩，显示出很高的丰度，但在同一个MgO中，镍的含量变化很大。围绕这种变异的起源存在争议。经过充分表征的样品将被用来评估是什么岩浆作用控制了夏威夷玄武岩中橄榄石中的镍丰度。基拉韦厄火山持续喷发产生的玄武岩和卡乌拉岛火山活动恢复阶段产生的碱性熔岩是该项目的重点。基拉韦厄火山喷发的岩浆过程众所周知，包括岩浆混合、晶体聚集和随时间变化的母岩浆成分。对于返老期熔岩，将利用橄榄石中的镍来研究其成因深度。目前的深度估计非常不稳定。之前还没有对返老还童熔岩中的橄榄石进行过高精度的分析。这一研究对进一步认识地幔玄武岩的源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.