Collaborative Research: Pa-231/U-235 Fractionation During Intra-Plate Mantle Melting and Magma Transport

合作研究：板内地幔熔融和岩浆输送过程中的 Pa-231/U-235 分馏

• 批准号: 9980545
• 负责人: Yemane Asmerom
• 金额: $ 9.8万
• 依托单位: University of New Mexico
• 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: 1999-11-15 至 2003-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9980545&HistoricalAwards=false
• 关键词: Collaborative; Research; Pa; 231; 235

Asmerom EdwardsEAR-9980545 EAR-9980605Basalts are our physical link to the mantle, which is the largest silicate domain in the earth. Variations in the chemical and isotopic composition of basalts may result from differences in their mantle sources or processes related to melting and melt transport. Continental basalts, although volumetrically not significant, may provide unique insights into mantle melting processes. Particularly interesting are the processes related to the enigmatic lithospheric mantle melting and the role of the lithosphere during the dynamic melting of the underlying asthenosphere. Unlike long-lived isotopic systems, which provide time-integrated data, the short-lived uranium series isotopes may provide unique constraints on extent and timing of melting and melt transport. These constraints are possible because the source nuclide ratios are known (equal to the ratio of the half-lives of the nuclides in any chain) and the half-lives are of time-scales appropriate for mantle melting and transport. The two important uranium-series isotopic systems for the study of mantle melting are 230Th-238U and 231Pa-235U. The 231Pa-235U system can be a powerful complement to the more-developed 230Th-238U method once we gain understanding of the ways in which 231Pa and 235U behave during melting. At the present there are very few 231Pa-235U data on basalts. We expect results from this project will enlarge our understanding of 231Pa-235U fractionation during melting and melt transport. In addition to whole-rock data, we will obtain mineral/matrix Pa data. At the present there are no mineral/melt partitioning data for Pa. Uranium-series isotopic data from this project will provide important constraints for melting and magma transport models.

Asmerom 玄武岩是我们与地幔的物理联系，地幔是地球上最大的硅酸盐域。 玄武岩的化学和同位素组成的变化可能是由于它们的地幔来源或与熔融和熔融输送有关的过程的差异。 大陆玄武岩，虽然体积不显着，可能提供独特的见解地幔熔融过程。特别令人感兴趣的是与神秘的岩石圈地幔熔融过程和岩石圈在下伏软流圈动态熔融过程中的作用。 与提供时间综合数据的长寿命同位素系统不同，短寿命铀系列同位素可能对熔化和熔体输送的范围和时间提供独特的限制。 这些限制是可能的，因为源核素比率是已知的（等于任何链中核素的半衰期比率），半衰期的时间尺度适合于地幔熔融和迁移。 230 Th-238 U和231 Pa-235 U是研究地幔熔融的两个重要铀系同位素体系。 一旦我们了解了231 Pa和235 U在熔融过程中的行为方式，231 Pa-235 U系统可以成为更先进的230 Th-238 U方法的有力补充。 目前玄武岩的~（231）Pa-~（235）U数据很少。 我们期望这个项目的结果将扩大我们对熔融和熔融输送过程中231 Pa-235 U分馏的理解。 除全岩数据外，我们还将获得矿物/基质Pa数据。 目前没有Pa的矿物/熔体分配数据。 该项目的铀系同位素数据将为熔融和岩浆迁移模型提供重要的约束。