Nb/Ta Fractionations as Tracer of Subduction

Nb/Ta 分数作为俯冲示踪剂

• 批准号: 0635864
• 负责人: Vincent Salters
• 金额: $ 29.91万
• 依托单位: Florida State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-12-01 至 2010-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0635864&HistoricalAwards=false
• 关键词: Nb; Ta; Fractionations; Tracer; Subduction

Intellectual merit. Using current estimates for the composition of the Earth's principal reservoirs, mass balance for niobium (Nb) and hafnium (Hf) does not add up and some Nb and Hf is unaccounted for. This proposal is aimed at testing the hypothesis of the existence of a mantle reservoir that contains the balance of the Nb and Hf. This "hidden" reservoir would be high in Nb/Ta and/or low in Lu/Hf. The recognition of such a reservoir would have significant implications for understanding mantle evolution and the recycling of crustal components back into the mantle. Subducted oceanic crust may be the key to solving the apparent mass balance problem. However, for oceanic crust to be the postulated hidden reservoir, it needs to lose Ta compared to Nb in the subduction process. Nb/Ta is an especially useful petrogenetic tracer because very few processes can fractionate these elements (given their similar chemical properties), and thus it can become a very reliable indicator of recycled material. However, because the total variation is limited, high precision analyses are required to recognize the variations. Low-precision analyses of island arc volcanics indicate that there is a significant fractionation in Nb/Ta during subduction. However, the "when" and "where" of the Nb/Ta fractionation is unknown. We propose to determine the behavior of these and other elements in subducted material from various stages of subduction to determine the reaction(s) that result in the fractionation of Nb from Ta and to characterize the material that is subducted. We will work on natural materials as the experimental evidence on elemental partitioning is inconclusive. Once the fractionation process is identified the Nb/Ta can be used as a fingerprint of that process. We complement the analyses of the subducted material with analyses of island arc samples - with the aim to understand where in the subduction process Nb and Ta fractionate. Broader impacts. One outcome will be development of "new" high precision trace element analytical methods that will have wide applicability. This project will support a young scientist and a graduate student and it will provide core support for the operation of the laboratory, which the PI tries to operate as an open use facility, especially for students. In combination with existing programs at the National High Magnetic Field Laboratory (NHMFL) the proposed research will train and educate undergraduate students as well as teachers. The presence of an active research program is an essential component in being able to expose students and teachers to scientific discovery.

智力优点。使用目前的地球主要储层组成的估计值，Niobium（NB）和Hafnium（HF）的质量平衡不会加起来，并且某些NB和HF的质量不计。 该建议旨在检验包含NB和HF平衡的地幔储层存在的假设。 这个“隐藏”的水库在NB/TA中很高，在LU/HF中为/或低。 对这种储层的认识将对理解地幔进化以及将地壳成分回收回到地幔具有重要意义。 俯冲的海洋壳可能是解决明显的质量平衡问题的关键。 但是，要使海洋壳是假定的隐藏储层，与俯冲过程中的NB相比，它需要损失TA。 NB/TA是一种特别有用的岩发生示踪剂，因为很少的过程可以将这些元素分离（鉴于它们相似的化学特性），因此它可以成为回收材料的非常可靠的指标。 但是，由于总变化是有限的，因此需要高精度分析才能识别变化。对岛弧火山的低精度分析表明，在俯冲过程中，NB/TA有明显的分馏。 但是，尚不清楚NB/TA分馏的“何时”和“何处”。 我们建议从俯冲的各个阶段确定这些和其他元素在俯冲材料中的行为，以确定导致NB从TA分馏的反应，以表征俯冲的材料。 我们将研究天然材料，因为有关元素分配的实验证据尚无定论。 一旦确定了分馏过程，NB/TA可以用作该过程的指纹。 我们通过对岛弧样品的分析进行了对俯冲材料的分析 - 旨在了解俯冲过程中的nb和Ta分数中的位置。 更广泛的影响。一个结果将是开发具有广泛适用性的“新”高精度痕量分析方法。 该项目将支持一位年轻的科学家和研究生，它将为实验室的运营提供核心支持，PI试图作为开放用途设施，尤其是针对学生。 结合国家高磁场实验室（NHMFL）的现有计划，拟议的研究将培训和教育本科生和教师。 积极研究计划的存在是能够使学生和教师了解科学发现的重要组成部分。