U-Series Isotope Systematics of Continental Rift Basalts: The Rio Grande Rift, USA

9706373阿斯梅罗姆裂谷是一种独特的构造环境，其中既有来自深部地幔的岩浆，也有来自古老岩石圈大陆地幔的岩浆。裂谷中喷发的大陆玄武岩的化学和同位素研究可以为我们提供大陆下地幔组成的信息。 与长寿命同位素系统相反，短寿命核素，如U系列同位素，使我们能够追踪现今壳幔系统的动力学和成分方面。研究区域，格兰德河裂谷及其边缘，是美国大陆裂谷系统最具特色的地区之一。它包含同时代的年轻碱性和拉斑玄武岩的假定软流圈和岩石圈地幔起源在空间上接近。这些玄武岩的U系列同位素数据和Pb、Sr、Nd同位素组成有助于我们了解：（1）控制大陆玄武岩Th富集变化的因素，如熔融程度、熔融速率和地幔熔融深度（源区）的差异。 地幔源区随时间变化的信息为大陆裂谷作用模型提供了约束条件。 2)大陆下地幔的Th-U成分变化，特别是大陆岩石圈地幔232 Th/238 U比值（k值）的变化。关于k值的信息对于全球物质平衡和作为地幔中的再循环和交代作用等过程的指标是重要的。3)大陆地壳在改变裂谷岩浆化学性质方面的作用。

9706373 Asmerom Rifts are unique tectonic settings where magmas derived from both the deep mantle and the old lithospheric continental mantle occur. Chemical and isotopic studies of continental basalts erupted in rifts can provide us with information on the mantle composition under the continents. In contrast to long-lived isotope systems, short-lived nuclides, such as the U-series isotopes, allow us to trace dynamical and compositional aspects of the present-day crust-mantle system. The study area, the Rio Grande Rift and its cratonic margins, is one of the best characterized continental rift systems in the US. It contains contemporaneous young alkali and tholeiitic basalts of presumed asthenospheric and lithospheric mantle origin in close spatial proximity. The U-series isotopic data in conjunction with Pb, Sr and Nd isotopic compositions of these basalts will contribute to our understanding of: 1) controls on the variation of Th enrichment in continental basalts such as differences in degree and rate of melting, and depth (source) of mantle melting. Information on the variation of mantle sources with time provides constrains for models of continental rifting. 2) Th-U compositional variability of the mantle under continents, and in particular the variability in the 232Th/238U ratio (k-value) of the continental lithospheric mantle. Information on the k-value is important with respect to global mass balance and as indicator of processes such as recycling and metasomatism in the mantle. 3) the role of continental crust in modifying the chemistry of rift magmas.