Collaborative Research: Melting and Mass Transfer in the Central American Arc From Pa-231, Th-230, and Ra-226 Systematics

合作研究：Pa-231、Th-230 和 Ra-226 系统学中美洲弧的熔化和质量传递

• 批准号: 9900461
• 负责人: Mark Reagan
• 金额: $ 4.07万
• 依托单位: University of Iowa
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-02-01 至 2003-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9900461&HistoricalAwards=false
• 关键词: Collaborative; Research; Melting; Mass; Transfer

9900461ReaganThe mechanism and timing of partial melting and melt extraction in the mantle beneath arcs constitutes one of the key unresolved questions regarding arc magmatism. This collaboration between researchers at the Universities of Minnesota and Iowa will use analyses of U-series nuclides and particularly of 231Pa in young volcanic rocks to better understand the melting process beneath the Central American arc and to determine how this process is affected by fluxes of components from the subducting slab. Preliminary studies show that 231Pa is strongly fractionated from U in the sub-arc mantle prior to eruption on a time scale similar to or less than the half life of 231Pa (33 kyr), strongly suggesting that 231Pa is a sensitive indicator of the timing and mechanism of melting and melt extraction. Measurements of (231Pa)/(235U) and (230Th)/(238U) activity ratios using thermal ionization mass spectrometry and (226Ra)/(230Th) ratios using alpha counting techniques will be made for an along-arc suite of young volcanic rocks from the southern Central American arc in Costa Rica and Nicaragua. The southern Central American arc is an ideal location for studying melting and mass transfer processes using U-series isotopes because many of the parameters affecting arc volcanism, such as the composition of the mantle and the mass flux of components from the subducting slab, vary across the region in a systematic and well-characterized fashion. The resulting data set will be to our knowledge the most complete study of U-series isotopes associated with an arc province, and combined with the trace element and long-lived isotopic data will yield a unique body of data against which hypotheses for melting and mass transfer in arcs can be tested.

9900461雷根弧下地幔部分熔融和熔融提取的机制和时间构成了弧岩浆活动的关键未解决的问题之一。 明尼苏达大学和爱荷华州大学的研究人员之间的这项合作将使用对年轻火山岩中U系列核素，特别是231 Pa的分析，以更好地了解中美洲弧下的熔融过程，并确定这一过程如何受到俯冲板片成分通量的影响。 初步研究表明，在喷发前，231 Pa在弧下地幔中与U强烈分馏，其时间尺度类似于或小于231 Pa（33 kyr）的半衰期，这强烈表明231 Pa是熔融和熔融提取的时间和机制的敏感指标。 本文对中美洲弧南部哥斯达黎加和尼加拉瓜的一套年轻火山岩进行了（231 Pa）/（235 U）和（230 Th）/（238 U）活度比值的热电离质谱测量和（226 Ra）/（230 Th）比值的α计数测量。中美洲南部的弧是一个理想的位置，研究熔化和质量转移过程中使用U系列同位素，因为许多参数影响弧火山作用，如地幔的成分和质量流量的组件从俯冲板，在整个地区的变化在一个系统和良好的特点。由此产生的数据集将是我们所知的最完整的研究与弧省的U系列同位素，并结合微量元素和长寿命同位素数据将产生一个独特的身体的数据对熔化和质量转移的假设弧可以测试。