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

Amerom EdwardsEAR-9980545 EAR-9980605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区域。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体运输有关的过程的不同所致。大陆玄武岩虽然在体积上并不重要，但可以为地幔熔融过程提供独特的见解。特别令人感兴趣的是与神秘的岩石圈地幔熔融有关的过程，以及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运输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的比率)，并且半衰期具有适合于地幔熔化和运输的时间尺度。研究地幔熔融的两个重要的铀系同位素系统是230Th-238U和231Pa235U。一旦我们了解了231Pa235U在熔化过程中的行为，231Pa235U系统可能是对更发展的230Th-238U方法的有力补充。目前有关玄武岩的231Pa235U资料很少。我们希望这个项目的结果将扩大我们对231Pa235U在熔融和熔体输送过程中分馏的理解。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。该项目的铀系同位素数据将为熔融和岩浆运移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.