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

橄榄石中镍的系统学作为夏威夷玄武岩岩浆过程的指纹

• 批准号: 1347915
• 负责人: Michael Garcia
• 金额: $ 16.72万
• 依托单位: University of Hawaii
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-02-01 至 2016-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1347915&HistoricalAwards=false
• 关键词: Ni; Systematics; Olivine; Fingerprints; Magmatic

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.

橄榄石矿物对理解上地幔和地壳过程具有重要意义。橄榄石中的镍（Ni）含量是温度、压力、氧逸度和体成分的敏感指标，因此引起了人们的极大兴趣。影响镍在橄榄石中平衡分配的因素已经通过广泛的实验条件和组成进行了大量的实验研究。然而，由于岩浆系统的复杂过程，镍和其他二价离子在橄榄石中的行为仍然知之甚少。海洋岛屿玄武岩，如夏威夷的玄武岩，显示出橄榄石镍含量的巨大变化。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。这些熔岩含镍范围广，岩浆历史特征明显。通过对已知岩浆历史岩石中含镍相的主微量元素分析，评价各岩浆过程对橄榄石中镍的控制作用。幔源岩浆的早期结晶史以橄榄石为主。通常，它是唯一一种在原始夏威夷玄武岩中，在低到中等压力下，低于液相线100℃结晶的矿物。橄榄石的组成被广泛用于评价各种岩浆过程，包括结晶史、岩浆混合聚集和污染过程。橄榄石的镍含量因其在幔源熔岩中的强配伍性而备受关注，并被认为对解释岩心的形成、地幔的性质和演化、地幔中的熔体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地球过程提供了有价值的视角。与羽流相关的熔岩，如夏威夷的羽流熔岩，在相同的MgO中显示出高丰度，但镍含量差异很大。关于这种变体的起源存在争议。具有良好特征的样品将用于评估哪些岩浆过程负责控制夏威夷玄武岩橄榄石中的Ni丰度。基拉韦厄火山正在喷发的拉斑玄武岩和Ka 'ula岛火山活动复兴阶段的碱性熔岩是这个项目的重点。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、结晶聚集和母岩浆组成的时间变化。对于恢复阶段的熔岩，将利用橄榄石中的镍来研究其起源深度。目前的深度估计是高度可变的。在此之前，还没有对复活熔岩中的橄榄石进行高精度分析。该研究对幔源玄武岩的物源岩性和形成条件的认识具有指导意义。