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基于对熔融或部分熔融物质结晶的岩石的研究，了解目前地壳和地幔(地球的两个主要结构成分；第三个成分是地核)的化学成分。虽然地球内部的样本偶尔会在火山喷发中携带，但有关地幔化学成分的许多信息必须从地球表面上升并喷发的部分熔体(这些岩石被称为玄武岩)中推断出来。进入地幔的两个最佳“窗口”是来自大洋中脊(MOR)的玄武岩和来自海洋岛屿(如夏威夷)的玄武岩。虽然岩石学家对大洋中脊玄武岩的起源(例如，熔化产生这些岩石的地幔的组成)有很好的零级理解，但对于大洋岛屿玄武岩就不是这样了，目前文献中正在辩论几种假说。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来源的地幔来源与莫尔玄武岩来源的地幔来源有多大不同的问题。回答这个问题对于理解地球地幔的化学不均一性和在地球表面形成岩石的过程具有重要的意义。矿物橄榄石通常存在于来自MORS、洋岛和大陆泛滥玄武岩省的玄武岩中，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的橄榄石也具有低的FeO/MnO，而高NiO的橄榄石往往具有高的FeO/MnO)。阵列的低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、留尼汪岛和卡鲁岩的橄榄石定义，其NiO含量可高达~0.6wt%。尖晶石二辉橄榄岩(这种岩石类型被认为代表了上地幔的主体和莫尔玄武岩的来源)的橄榄石大约位于阵列的中间，NiO值在0.35-0.40wt%之间。解释这种全球阵列的大部分努力都集中在高NiO-FeO/MnO部分上，因为很难产生具有正常地幔浓度的NiO的尖晶石二辉橄榄岩的部分熔体，该部分熔体将结晶出具有0.4wt%NiO的橄榄石，使用任何常见的基于1-ATM的表达式在橄榄石和玄武岩熔体(指定为DNI)之间分配NiO。迄今为止的模式包括不含橄榄石源的熔融(尖晶石二辉橄榄岩和被俯冲回地幔的洋壳富硅熔体的混合物)，在显示这些高NiO-Fe/Mn橄榄石的熔岩来源中添加少量外核(富含Ni和Fe)，以及DNI随压力和温度而变化的观点。定量计算尖晶石二辉橄榄岩或地幔岩石的部分熔体中观察到的NiO和FeO/MnO含量的努力，以及在上升过程中从这些熔体结晶的橄榄石，由于缺乏计算液体和共存晶相的NiO和MnO含量的高压和温度D而受阻。这个项目的目标是在一定的压力、温度和块体成分范围内确定橄榄石和玄武岩熔体之间的一组NiO和MnO分配系数，然后使用这些实验确定的值来评估提出的解释全球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.