Secular Evolution in the Composition of the Mantle

9506517 Jacobsen现今地幔的成分变化是由地质时期的许多壳幔和地幔内分异过程造成的。 其中一些古老的过程与今天发生的过程有着明显的不同。 大陆地壳的形成对现今地幔的组成有着最大的影响，但这究竟是如何以及何时发生的却存在争议。 建议对现代和古代镁铁质至超镁铁质熔岩及其熔融包裹体进行一系列高质量的地球化学测量，这将对地幔成分的长期演化产生新的见解。 这些研究中最重要的是将使用微束技术对古熔岩中的橄榄石熔融包裹体进行研究，以确定原生熔岩及其源区的成分特征。 科马提岩样品含有橄榄石托管熔融包裹体从广泛变化的时间和空间协会将进行调查。 这些微束技术也将被应用于确定现代海洋玄武岩的玻璃质部分的成分，以建立在熔岩及其源区的不相容元素的“恒定比例”的变化。 描述地幔成分的长期演化将有助于加深对壳幔和地幔内分异过程及其发生速率的理解。

9506517 Jacobsen The compositional variation of the present-day mantle results from a number of crust-mantle and intra-mantle differentiation processes operating over geologic time. Some of these ancient processes many have been markedly different from those occurring today. The production of continental crust has had the greatest influence in establishing the composition of the present-day mantle, but exactly how and when this occurred is controversial. It is proposed to conduct a series of high quality geochemical measurements of modern and ancient mafic to ultramafic lavas and their melt inclusions that will yield new insights into the secular evolution in the composition of the mantle. Foremost among these studies will be the use of microbeam techniques on olivine-hosted melt inclusions in ancient lavas to determine the compositional characteristics of the primary lavas and their source regions. Komatiitic samples containing olivine-hosted melt inclusions from widely varying temporal and spatial associations will be investigated. These microbeam techniques will also be applied to determine the compositions of glassy portions of modern oceanic basalts in order to establish variations in "constant ratios" of incompatible elements in the lavas and their source regions. Characterizing the secular evolution of the composition of the mantle will lead to a enhanced understanding of crust-mantle and intra-mantle differentiation processes and the rate at which they occurred.