Chemical Dynamics of Mantle Lithosphere from Th Isotope Systematics

9418323里德美国西部地幔岩石圈Th-Pb同位素变化的起源将通过研究三个地区的玄武岩来研究：西部大盆地(WGB)、蛇河平原(SRP)和科罗拉多高原西部及其过渡带。这些区域突出了可能对熔岩的最终Th-Pb特征产生重大控制作用的互补和对比过程，包括岩石圈形成和矿物学(所有区域)、与俯冲有关的地幔源交代作用(WGB和SRP)以及与羽流有关的地幔源富集(SRP)。到目前为止所获得的结果反映了其中两个地区的有限采样，但表明Th同位素不平衡可能与部分熔融过程有关，并与地幔储集层及其成因有关。将从美国西部的构造岩浆省获得晚更新世至全新世玄武岩的Th同位素数据，因为它们可能对地幔岩石圈的性质和演化产生重要的制约。除了Th，这些玄武岩还将以其锶、钕和铅的同位素组成为特征。在完整的常量、痕量元素和同位素分析的框架内，将利用U-Th同位素体系的不平衡来考虑玄武岩岩浆中部分熔融的条件和岩石圈特征的可能来源。

9418323 Reid The origin of Th-Pb isotope variations in mantle lithosphere beneath the western USA will be investigated by examining basalts from three areas: the Western Great Basin (WGB), Snake River Plain (SRP), and western Colorado Plateau and its transition zone. These areas highlight complementary and contrasting processes that may have exerted significant control on the ultimate Th-Pb characteristics of the lavas including lithosphere formation and mineralogy (all areas), subduction-related metasomatism of mantle sources (WGB and SRP), and plume-related enrichment of mantle sources (SRP). Result obtained to date reflect a limited sampling of two of these areas but show that Th isotope disequilibria can be related to processes of partial melting and to characterizing mantle reservoirs and their origin. Th isotope data will be obtained for late Pleistocene to Holocene basalts from tectonomagmatic provinces in the western USA selected for their likelihood to yield important constraints on the nature and evolution of mantle lithosphere. In addition to Th, these basalts will be characterized for their Sr, Nd, and Pb isotope compositions. Within the framework of complete major and trace element and isotope analyses, disequilibrium in U-Th isotope systematics will be used to consider the conditions of partial melting and possible origins for lithospheric signatures in basaltic magmas.