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

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。玄武岩化学和同位素组成的变化可能是由于其地幔来源的不同或与熔融和熔体运输有关的过程的不同。大陆玄武岩虽然在体积上不重要，但可能为地幔融化过程提供独特的见解。特别有趣的是与神秘的岩石圈地幔融化和岩石圈在底层软流圈动态融化中的作用有关的过程。与提供时间集成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程度和时间提供独特的限制。这些限制是可能的，因为源核素比是已知的（等于任何链中核素的半衰期之比），而且半衰期的时间尺度适合于地幔熔化和运输。230Th-238U和231Pa-235U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231Pa和235U在熔化过程中的行为方式，231Pa-235U系统可以成为更发达的230 - 238u方法的有力补充。目前关于玄武岩的231Pa-235U资料很少。我们期望这个项目的结果将扩大我们对231Pa-235U在熔融和熔体运输过程中的分馏的理解。除了全岩数据外，我们还将获得矿物/基质Pa数据。目前还没有Pa的矿物/熔体分配数据。该项目的铀系列同位素数据将为熔融和岩浆输送模型提供重要的约束条件。

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.