A New Window into Magmatic Processes: Zoning of Phosphorus and Other Elements in Olivine

智力上的优点。这个项目探讨了最近发现的橄榄石中磷分带的意义和实用性，这些橄榄石来自陆地科马提岩、玄武岩、安山岩和英安岩，以及月球岩石和火星陨石。这些橄榄石的P2 O 5含量从低于检测值（0.01 wt. %）至0.2- 0.4wt. %，Fo含量没有相关变化。磷分带可以描绘富磷的晶体核心与骨骼，漏斗，或自形形状;各种类型的振荡分区;结构，建议溶解沉淀;和部门分区。在恒定冷却速率（15-30 ℃/小时）下对高镁模型夏威夷玄武岩进行的结晶实验再现了许多这些特征。据推测，合成和天然橄榄石中的富磷区反映了橄榄石快速生长过程中P的掺入，分区模式主要记录晶体生长速率的变化。在实验和一些天然橄榄石（例如，微斑晶），Al含量与Cr和P均呈线性正相关，表明存在耦合置换。然而，在斑晶，铬分区往往是不那么强烈的P分区，和铝分区是弱到absent.The的前提下，这个建议是，元素地图的P和相关元素的橄榄石代表了一个潜在的档案有关岩浆过程的信息，在很大程度上是未知的，因此未开发。本提案中所述的实验项目旨在提供对控制分区发展的因素的定量了解，并利用扩散弛豫来推断岩浆过程的时间尺度。具体任务包括：（1）确定冷却速率对橄榄石吸磷的影响，并对磷的橄榄石-液体分配系数进行约束。(2)确定体Cr和Al浓度和fO 2对橄榄石和硅酸盐熔体之间动力学驱动的P分配的影响。(3)橄榄石中铝、铬和磷的扩散系数的限制。(4)对天然橄榄石中P、Cr和Al分带的进一步表征，特别强调来自夏威夷熔岩、MORB、科马提岩、高Al玄武岩等的微斑晶。该提案中描述的项目符合NSF的几个更广泛影响的标准：（1）该提案资助的主要研究人员是女性，加强了NSF“与代表性不足的群体成员建立研究合作”的任务。(2)一名研究生将承担本提案中所述的部分工作，从而推进研究生教育。(3)这些项目的成果将迅速在地质文献中发表，并在国家会议上介绍，以便向广大受众传播成果。(4)来自加州理工学院和其他学术机构的本科生继续在实验岩石学实验室做暑期研究项目-这是一个让学生接触到一个不属于标准地球科学课程的学科研究的外展活动。这些活动符合NSF整合研究和教育的目标。

Intellectual merit. This project explores the significance and utility of recent discovery of phosphorus zoning in olivines from terrestrial komatiites, basalts, andesites, and dacites and from lunar rocks and a Martian meteorite. P2O5 contents of these olivines vary from below detection (0.01 wt. %) to 0.2-0.4 wt. % over a few microns, with no correlated variations in Fo content. P zoning can delineate P-rich crystal cores with skeletal, hopper, or euhedral shapes; various types of oscillatory zoning; structures suggesting solution-precipitation; and sector zoning. Crystallization experiments on high-Mg, model Hawaiian basalts at constant cooling rates (15-30 C/hr) reproduce many of these features. It is inferred that P-rich zones in synthetic and natural olivines reflect incorporation of P during rapid olivine growth and that the zoning patterns primarily record crystal-growth-rate variations. In experimental and some natural olivines (e.g., microphenocrysts), Al contents are linearly and positively correlated with both Cr and P, suggesting coupled substitutions. However, in phenocrysts, Cr zoning is often less intense than P zoning, and Al zoning is weak to absent.The premise of this proposal is that elemental maps of P and associated elements in olivines represent a potential archive of information regarding magmatic processes that is largely unknown and therefore untapped. The experimental projects described in this proposal are designed to provide a quantitative understanding of factors controlling development of the zoning and the use of diffusive relaxation to infer time scales of magmatic processes. Specific tasks include: (1) Determining the effects of cooling rate on phosphorus uptake in olivine and constraining the olivine-liquid partition coefficient for phosphorus. (2) Determining the effects of bulk Cr and Al concentrations and fO2 on kinetically driven P partitioning between olivine and silicate melt. (3) Constraining Al, Cr, and P diffusivities in olivine. (4) Further characterization of P, Cr, and Al zoning in natural olivines, with particular emphasis on microphenocrysts from Hawaiian lavas, MORBs, komatiites, high-Al basalts, etc.Broader impacts. Projects described in this proposal meet several NSF criteria for broader impacts: (1) The primary researcher funded by this proposal is a woman, strengthening the NSF mandate to "establish research collaborations with members of underrepresented groups". (2) A graduate student will undertake part of the work described in this proposal thus advancing graduate student education. (3) Results of these projects will be promptly published in the geologic literature and presented at national conferences in order to disseminate the results to a broad audience. (4) Undergraduates from Caltech and other academic institutions continue to do summer research projects in the experimental petrology laboratory - an outreach that exposes students to research in a discipline that is not part of the standard earth science curriculum. These activities are in accordance with the NSF goal of integrating research and education.