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

火成岩岩石学的一个基本目标是通过对熔融或部分熔融物质结晶的岩石的研究，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核）目前的化学成分。虽然地球内部的样本偶尔会被火山喷发带上来，但关于地幔化学成分的大部分信息必须从地球表面上升和喷发的部分熔体（这些岩石被称为玄武岩）中推断出来。进入地幔的两个最好的“窗口”是来自洋中脊（MOR）的玄武岩和来自海洋岛屿（如夏威夷）的玄武岩。虽然岩石学家对洋中脊玄武岩的起源有一个很好的零阶理解（例如，融化产生这些岩石的地幔包裹的组成），但对于洋岛玄武岩却不能说同样的话，目前文献中有几个假设正在争论中。这里提出的实验研究旨在帮助区分这些相互竞争的假设，这些假设主要围绕着洋岛玄武岩源的地幔源与MOR玄武岩源的地幔源有何不同的问题。回答这个问题对于理解地球地幔的化学非均质性和产生地球表面岩石的过程具有重要意义。在MORs、海洋岛屿和大陆洪泛玄武岩省的玄武岩中普遍存在矿物橄榄石，对大量这些橄榄石的分析表明，它们的NiO和FeO/MnO浓度呈正相关（低NiO的橄榄石也具有低FeO/MnO，而高NiO的橄榄石往往具有高FeO/MnO）。低NiO- feo /MnO端由来自MORB和冰岛岩石的橄榄石定义，而高NiO- feo /MnO端主要由来自夏威夷，r<s:1> union和Karoo岩石的橄榄石定义，其NiO含量可达~0.6 wt%。尖晶石橄榄石（被认为代表了大部分上地幔和MOR玄武岩来源的岩石类型）的橄榄石大约位于阵列的中间，NiO值为0.35-0.40 wt%。解释这一全球阵列的大部分努力都集中在高NiO- feo /MnO部分，因为很难产生具有正常地幔NiO浓度的尖晶石-辉橄榄岩的部分熔体，这将使含有0.4 wt% NiO的橄榄石结晶，使用任何常见的基于1原子的表达式来划分NiO在橄榄石和玄武岩熔体之间（称为DNi）。迄今为止的模型包括无橄榄石来源的熔融（尖晶石橄榄岩和富含硅的海洋地壳熔融物的混合混合物，这些熔融物已经俯冲回地幔），向显示这些高NiO-Fe/Mn橄榄石的熔岩来源添加少量外核（富含Ni和Fe），以及DNi随压力和温度变化的想法。由于缺乏用于计算液体和共存结晶相中NiO和MnO含量的高压和温度Ds，定量计算少量或不含橄榄石的尖晶石橄榄岩或地幔岩石部分熔体中观察到的NiO和FeO/MnO含量的努力受到了阻碍。该项目的目标是确定一系列橄榄石和玄武岩熔体在压力、温度和体积成分范围内的NiO和MnO分配系数，然后，使用这些实验确定的值来评估已经提出的解释全球NiO- feo /MnO阵列的不同假设。

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.