Mantle Composition as a Function of Crustal Tectonics, Southwestern U.S.

本文研究了盆山省和邻近的科罗拉多高原以及两省之间的过渡带中来自地幔的尖晶石橄榄岩包体的地球化学特征。研究的核心是分析和模拟从块状橄榄岩中分离出的单斜辉石的稀土元素和锶、钕同位素组成，但捕虏体的种群系统学和矿物组成将被调查，在选择具有代表性的样品进行研究时尤为重要。除了标准的分析技术外，二次离子质谱仪还将用于测量单个CPX颗粒中的相对稀土丰度。将描述这两个构造省下现今的地幔成分，并为每个地区建立一个模型。这将包括观察到的非均质性(或均质性)，以及在可能的情况下，推断的分馏事件的年龄和性质。最终，将综合所有地区的模型，为地幔成分的系统变化提供一个区域模型，因为它与大规模的地壳构造作用有关。

This is a study of the geochemistryof mantle-derived, spinel peridotite xenoliths from localities in the Basin and Range Province and the adjacent Colorado Plateau, as well as the transition zone between the two provinces. The heart of the study is the anlysis and modelling of the REE and Sr and Nd isotopic compositions of clinopyroxene seperated from the bulk peridotites, but xenolith population systematics and mineral composition will be investigated and will be particularly important in choosing representative samples for study. In addition to standard analytical techniques, secondary ion mass spectrometry will be utilized to measure relative REE abundances in single cpx grains. Present-day mantle composition beneath the two tectonic provinces will be characterized and for each locality a model will be developed. This will include observed heterogeneity (or homogeneity) and where possible, the inferred age and nature of fractionation events. Ultimately models for all localities will be integrated to provide a regional model for the systematic variation of mantle composition as it relates to large-scale crustal tectonism.