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

知识价值。这个项目探讨了最近发现的磷在橄榄石中的重要性和实用性，这些橄榄石来自陆地的科马长岩、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P2O5含量在几微米范围内从低于检测值（0.01 wt. %）变化到0.2-0.4 wt. %，而Fo含量没有相关变化。P分带可以圈定骨架状、漏斗状或自面体状的富P晶芯；各种类型的振荡分区；提示溶液沉淀的结构；还有部门分区。在恒定的冷却速率（15-30℃/小时）下对高镁模型夏威夷玄武岩进行结晶实验，再现了许多这些特征。由此推断，合成橄榄石和天然橄榄石中的富磷带反映了橄榄石快速生长过程中磷的掺入，其分带模式主要记录了晶体生长速率的变化。在实验橄榄石和一些天然橄榄石（如微斑晶体）中，Al含量与Cr和P均呈线性正相关，表明存在耦合取代。然而，在斑晶中，Cr分带往往不如P分带强烈，Al分带弱至不存在。这一建议的前提是，橄榄石中P元素和相关元素的元素图代表了一个潜在的关于岩浆过程的信息档案，这些信息在很大程度上是未知的，因此尚未开发。本建议中描述的实验项目旨在提供对控制分区发展的因素的定量理解，并利用扩散松弛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中磷吸收的影响，并限制橄榄石-液体对磷的分配系数。(2)确定了体积Cr、Al浓度和fO2对橄榄石和硅酸盐熔体动力学驱动P分配的影响。(3)限制Al、Cr和P在橄榄石中的扩散率。(4)进一步表征天然橄榄石中P、Cr和Al的分带，特别强调来自夏威夷熔岩、morb、komatiites、高铝玄武岩等的微斑晶。本提案中描述的项目符合NSF对更广泛影响的几个标准：(1)本提案资助的主要研究人员是一名女性，加强了NSF“与代表性不足的群体成员建立研究合作”的授权。(2)研究生将承担本提案中所述的部分工作，从而促进研究生教育。(3)这些项目的成果将及时发表在地质文献上，并在全国会议上发表，以便向广大读者传播。(4)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进行暑期研究项目——这是一种拓展，使学生接触到标准地球科学课程之外的学科研究。这些活动符合美国国家科学基金会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.