ABR: Axial Magma Chambers and Shallow Fractionation Processes: A Comparative Mineralogic and Petrologic Study of Three Ridge Segments

地幔源熔体的浅层分馏过程是海洋地壳形成的核心。在本研究中，我们将对三个具有不同AMC特征和熔融透镜体逐渐收缩和消失的洋中脊段的物性熔岩进行全面、系统和定量的矿物学和岩石学研究。这三个脊段分别是北纬9°30°和10°30°的东太平洋隆起和南纬26°的大西洋中脊，我们对这些脊段的样品进行了很好的主元素、微量元素、同位素比率和基线岩石学和矿物学研究。我们建议详细研究的样品包含斑晶和微斑晶组合，以及含有熔体包裹体的难熔巨晶。利用各种技术（点计数、诺玛斯基、晶体尺寸分布和电子探针），我们将确定不同晶体种群及其熔体包裹体的丰度、组成和组成带。这些数据将使用现有的岩石学工具进行解释，以限制与三个区域中存在的各种液体和固体相关的浅层分馏过程的顺序和相对重要性。这项研究的比较性质和大量的定量矿物学和岩石学限制将使我们能够测试关于AMC过程的许多现有想法，包括熔融透镜体是广泛岩浆混合的场所的概念。

Processes of shallow fractionation of mantle-derived melts are central to the creation of oceanic crust. In this study, we will undertake a comprehensive, systematic and quantitative study of the mineralogy and petrology of phyric lavas from three mid-ocean ridge segments with very different AMC characteristics and progressive shrinking and disappearance of the melt lens. The three ridge segments are the East Pacific Rise at 9 30'N, 10 30'N and the Mid- Atlantic Ridge at 26 S, for which we have samples that are well studied for major elements, trace elements, isotopic ratios, and baseline petrography and mineralogy. The samples we propose to study in detail contain phenocryst and microphenocryst assemblages, as well as refractory megacrysts containing melt inclusions. Using a variety of techniques (point counting, Nomarski, crystal size distributions, and electron microprobe) we will determine the abundances, compositions and compositional zoning of different crystal populations and their melt inclusions. These data will be interpreted using available petrologic tools to constrain the order and relative importance of identified processes of shallow fractionation relating the various liquids and solids present in each of the three areas. The comparative nature of the study and the wide variety of quantitative mineralogic and petrologic constraints will allow us to test numerous current ideas about AMC processes, including the notion that the melt lens is the site of extensive magma mixing.