Experimental Constraints on Crystal Liquid Ni and Mn Partitioning in Mafic and Ultramafic Systems

火成岩学的一个基本目标是了解地壳和地幔（地球的两个主要结构组成部分;第三个组成部分是地球的核心）的化学成分，基于对熔融或部分熔融物质结晶的岩石的研究。虽然地球内部的样本偶尔会在火山爆发中被携带上来，但关于地幔化学成分的许多信息必须从已经上升并喷发到地球表面的部分熔体中推断出来（这些岩石被称为玄武岩）。进入地幔的两个最好的“窗口”是来自大洋中脊（莫尔）的玄武岩和来自海洋岛屿（例如，夏威夷）。虽然岩石学家对洋中脊玄武岩的起源有很好的零级理解（例如，这些岩石是由地幔熔融形成的），但对于洋岛玄武岩来说，情况并非如此，目前文献中有几种假说正在争论之中。这里提出的实验研究旨在帮助区分这些相互竞争的假说，这些假说主要围绕着洋岛玄武岩源的地幔来源与莫尔玄武岩源的地幔来源有多大不同的问题。研究这个问题对于理解地球地幔的化学不均匀性和地球表面岩石的形成过程具有重要意义。矿物橄榄石通常存在于MORs，海洋岛屿，对大量橄榄石的分析表明，它们的NiO和FeO/MnO含量呈正相关（具有低NiO的橄榄石也具有低FeO/MnO，而具有高NiO的橄榄石倾向于具有高FeO/MnO）。 阵列的低NiO-FeO/MnO端由来自MORB和冰岛岩石的橄榄石限定，而高NiO-FeO/MnO端主要由来自夏威夷、留尼汪和卡鲁岩石的橄榄石限定，其NiO含量可高达~ 0.6wt%。来自尖晶石二辉橄榄岩（被认为代表上地幔的大部分和莫尔玄武岩的来源的岩石类型）的橄榄石大约位于阵列的中间，NiO值为0.35-0.40重量%。大部分的努力来解释这个全球性的阵列集中在高NiO-FeO/MnO部分，因为它是难以产生部分熔体的尖晶石二辉橄榄岩与正常地幔浓度的NiO，将结晶橄榄石与0.4重量%的NiO使用任何常见的1-atm为基础的表达式之间的NiO橄榄石和玄武岩熔体（指定为DNi）的分区。到目前为止的模型包括一个不含橄榄石的来源（尖晶石二辉橄榄岩加上富含二氧化硅的洋壳熔体的混合物，已经俯冲回地幔）的熔融，除了少量的外核（富含Ni和Fe）的熔岩源，显示这些高NiO-Fe/Mn橄榄石，以及DNi随压力和温度变化的想法。定量计算所观察到的部分熔体的尖晶石二辉橄榄岩或地幔岩的NiO和FeO/MnO含量，以及橄榄石，从这些熔体中结晶上升的努力受到阻碍，缺乏高压和温度Ds计算NiO和MnO含量的液体和共存的结晶相。这个项目的目标是确定一组NiO和MnO之间的分配系数橄榄石和玄武岩熔体在一定范围内的压力，温度和散装组合物，然后，使用这些实验确定的值来评估不同的假设，已经提出来解释全球NiO-FeO/MnO阵列。

A fundamental goal of igneous petrology is to understand the present chemical composition of the Earth's crust and mantle (two of the major structural components of the planet; the third component is the Earth's core) based on a study of rocks that crystallized from molten or partially molten material. Although samples of the Earth's interior are occasionally carried up in volcanic eruptions, much of the information concerning the chemical composition of the mantle must be inferred from partial melts that have risen and been erupted on the Earth's surface (these rocks are called basalts). Two of the best 'windows' into the mantle are basalts from mid-ocean ridges (MOR) and basalts from ocean islands (e.g., Hawaii). While petrologists have a good zeroth-order understanding of the origin of mid-ocean ridge basalts (e.g., the composition of the parcels of mantle that melt to produce these rocks), the same cannot be said for ocean island basalts and several hypotheses are currently being debated in the literature. The experimental study proposed here is designed to help distinguish between these competing hypotheses, which largely revolve around the question of how different the mantle sources of ocean island basalt source are to those of MOR basalts. Answering this question has important implications for understanding the chemical heterogeneity of the Earth's mantle and processes that produce rocks that are seen on the surface of the Earth.The mineral olivine is commonly found in basalts from MORs, ocean islands, and continental flood basalt provinces and analyses of a large number of these olivines show that their NiO and FeO/MnO concentrations are positively correlated (olivines with low NiO also have low FeO/MnO, while those with high NiO tend to have high FeO/MnO). The low NiO-FeO/MnO end of the array is defined by olivines from MORB and Icelandic rocks whereas the high NiO-FeO/MnO end is largely defined by olivines from Hawaiian, Réunion, and Karoo rocks, which can have NiO contents up to ~0.6 wt%. Olivines from spinel lherzolites (the rock type thought to represent the bulk of the upper mantle and the source of MOR basalts) lie approximately in the middle of the array with NiO values of 0.35-0.40 wt%. Much of the effort to explain this global array has focused on the high NiO-FeO/MnO portion, since it is difficult to generate partial melts of spinel lherzolite with normal mantle concentrations of NiO that will crystallize olivine with 0.4 wt% NiO using any of the common 1-atm-based expressions for the partitioning of NiO between olivine and a basaltic melt (designated as DNi). Models to date include melting of an olivine-free source (a hybrid mixture of spinel lherzolite plus silica-rich melt of oceanic crust that has been subducted back into the mantle), addition of small amounts of outer core (rich in Ni and Fe) to the sources of the lavas that display these high NiO-Fe/Mn olivines, and the idea that DNi varies with pressure and temperature. Efforts to calculate quantitatively the observed NiO and FeO/MnO contents of partial melts of spinel lherzolite or mantle rocks with little or no olivine as well as the olivines that crystal from these melts on ascent are hampered by a lack of high-pressure and temperature Ds with which to calculate NiO and MnO contents of liquids and coexisting crystalline phases. The goal of this project is to determine a set of NiO and MnO partition coefficients between olivine and basaltic melt over a range of pressures, temperatures, and bulk compositions and to, then, use these experimentally determined values to evaluate the different hypotheses that have been put forth to explain the global NiO-FeO/MnO array.