Studies on the Partitioning of Elements Between the Core, Mantle and Crust

智力上的优点。改进对地球形成和随后的核形成过程中普遍存在的压力、温度和气体逸度条件的了解，将大大提高我们对地球核和周围硅酸盐壳的组成的理解，特别是关于生热元素U、Th和K的丰度和分布的理解。这种见解对于理解驱动地球发电机、地幔对流和板块构造的能源来源，以及理解地球的挥发性元素库存和限制核-地幔交换的性质和程度至关重要。该提案要求提供资金来分析天然和合成样品的组成，重点是精确和准确地测定亲铁、亲硫和主要亲石元素的痕量丰度，以便确定金属(以及较小程度的硫化物)和硅酸盐体系的固-液、固-固和液-液分配系数。这些数据将被用来改进对核、地幔、地壳和整体硅酸盐地球整体成分的估计，并对核形成、壳幔演化和核幔交换过程中元素的分配提供定量的见解。拟议的研究的主要目标包括：(1)亲铁元素和一些亲硫元素在地球储集层(核-地幔-壳)和岩浆中的浓度和行为；(2)名义上亲石元素(如Nb、Ta、K、Th和U)在核形成过程中的丰度和行为，(3)地幔和地核中挥发性元素的收支。这些相关项目的结果将：(A)提高我们对这些元素在地球上的丰度和分布的了解；(B)这些元素在核-地幔和地幔-壳分异过程中的产额分配系数；(C)限制已经发生和/或正在发生核分离和核幔交换的条件；以及(D)更好地确定行星乌里数(产生的辐射热与总热损失的比率)。(1)洋脊、岛屿和弧形现代玄武岩的加权平均K/U为20,600+/-3600(2SD，n=50)。我们的MORB的K/U值(19,800+/-3400，n=43)与Jochum等人报道的有很大不同。(1983)，反映了在抽样和处理总体差异方面的差异。据估计，现代地幔的K/U值高于大陆地壳，可能含有硅酸盐地球K和U收支的50%，表明40K的放射性贡献更大。(2)现代玄武岩具有相对恒定的W/BA(0.00136+/-86，2Sd)，可与陆壳相媲美，推测为硅酸盐地球。由此，我们可以确定硅酸盐地球的W浓度(9.0+/-5.8ppbW)。利用这个修正值，我们检验了基于Os同位素的夏威夷苦橄岩的核-地幔交换假说，发现如果这些熔岩来自一个含3倍硅酸盐地球W(~27 ppb)的储集层和一个含516 ppb W(即约占地球W收支的96%)的岩芯，则核心成分的并入与W同位素数据是一致的。(3)新的实验数据(Corgne等)与氧逸度增加(最初接近IW-3，最后接近IW-2)下金属熔体和硅酸盐熔体之间的分配一致。我们的结果与一个核的结果是一致的，这个核包含了一小部分行星预算中的锌、镓、钾、铜、锰、铬、Nb和Ta。已经提出了一个超软骨体Nb/Ta比值，但我们的数据表明上限为~15 ppb Ta。我们的模型预测了一个至少含有10ppm钛的核心。此外，地核预计将包含行星预算K的10%，但这一估计可能接近1%或更少。更广泛的影响。学生参与(研究生、本科生和高中)是我在UMD研究计划的一个基本方面。学生参与实践研究，这提供了重要的教育和培训机会，学生可以转化为未来在学术界、行业或政府的工作。该项目将支持一名博士生和两名本科生研究人员。我在教育、服务和外展方面的记录远远超出了科学界，进入了公共领域(K-12讲座，马里兰日开放参观实验室和分析，在我的质谱分析实验室参加为期一年的研究项目的高中实习生)，并在本提案的正文中进行了全面描述。

Intellectual merit. Improved knowledge of the pressure, temperature and gas fugacity conditions prevalent during the formation of the Earth and subsequent core formation would substantially enhance to our understanding of the composition of the Earth's core and surrounding silicate shell, particularly with respect to the abundance and distribution of the heat-producing elements U, Th and K. Such insights are essential for understanding the energy sources that drive the geodynamo, mantle convection and plate tectonics, as well as understanding the volatile element inventory of the planet and constraining the nature and degree of core-mantle exchange. This proposal requests funds to analyze the compositions of natural and synthetic samples, with emphasis on precise and accurate determinations of trace abundances of siderophile, chalcophile and key lithophile elements in order to establish solid-liquid, solid-solid and liquid-liquid distribution coefficients for metallic (and to a lesser extent sulfidic) and silicate systems. These data will be used to develop improved estimates of bulk compositional of the core, mantle, crust and bulk silicate Earth, and to provide quantitative insights into the partitioning of elements during core formation, crust-mantle evolution, and core-mantle exchange.The main goals of the proposed study include determining: (1) the concentration and behavior of siderophile and some chalcophile elements in Earth reservoirs (core-mantle-crust) and magmas, (2) the abundance and behavior of nominally lithophile elements (e.g., Nb, Ta, K, Th, and U) during core formation, and (3) the budget of volatile elements in the mantle and core. Results from these interrelated projects will (a) improve our understanding of the abundance and distribution of these elements in the Earth, (b) yield distribution coefficients for these elements during core-mantle and mantle-crust differentiation, (c) constrain the conditions under which core separation and core-mantle exchange has occurred and/or is occurring, and (d) better define the planetary Urey number (ratio of radiogenic heat production to total heat loss). The most important findings of my group's previous investigations (described in this proposal) include: (1) Modern basalts from ocean ridges, islands and arcs have a weighted average K/U of 20,600+/-3600 (2sd,n = 50). Our K/U value for MORB (19,800 +/- 3400, n=43) differs significantly from that reported by Jochum et al. (1983), reflecting differences in sampling and treatment of the population variance. The modern mantle is estimated to have a K/U value higher than the continental crust and likely contains 50% of the K and U budget of the silicate Earth, indicating a larger radioactive contribution of 40K. (2) Modern basalts have relatively constant W/Ba (0.00136 +/- 86, 2sd), which is comparable to the continental crust and by inference represents the silicate Earth. From this, we can establish the W concentration of the silicate Earth (9.0 +/- 5.8 ppb W). Using this revised value we tested the hypothesis of core-mantle exchange proposed for Hawaiian picrites based on Os isotopes and found that the incorporation of a core component is consistent with W-isotope data, if these lavas are derived from a reservoir with 3x silicate Earth W content (~27 ppb) and a core containing 516 ppb W (i.e., ~96% of the Earth's W budget). (3) New experimental partitioning data (Corgne et al) between molten metal and silicate melt are consistent with core formation under increasing oxygen fugacity (initially near IW-3 and finishing near IW-2). Our results are consistent with a core containing a fraction of the planetary budget of Zn, Ga, K, Cu, Mn, Cr, Nb and Ta. A superchondritic Nb/Ta ratio has been proposed for the core, but our data place the upper limit at ~15 ppb Ta. Our model predicts a core with at least 10 ppm Ti. Moreover, the core is predicted to contain 10% of the planetary budget of K, but this estimate is likely closer to 1% or less. Broader impacts. Student participation (at the graduate, undergraduate and high school levels) is a fundamental aspect of my research program at UMD. Students participate in hands-on research, which provides important educational and training opportunities that the students can translate to future work in academia, industry or government. This project will support one PhD student and two undergraduate researchers. My record in education, service and outreach extends well beyond the scientific community and into the public realm (K-12 lectures, Maryland Day open house lab tours and analyses, high school interns on year-long research programs in my mass spectrometry laboratory) and is described, in full, in the body of this proposal.