Melt Inclusion Study of Water and Chlorine Abundances in HIMU- and EM-type Mantle

该项目将研究挥发性丰度（水，CO2，Cl和S）的橄榄石托管熔融包裹体熔岩从南极岛链。 以前对这些岛屿熔岩的研究表明，三种不同的地幔成分参与其中，其中一种成分被认为来自古老的再生海洋地壳。 挥发性元素丰度和物种形成数据将结合主要和微量元素数据以及原位铅同位素数据，以评估有关这些熔岩的成因及其地幔来源的性质的几个基本问题。 具体的问题，将得到解决包括：（一）Cl浓度和Cl/K2 O比在南方群岛熔融包裹体的变化来自浅熔体/地壳或熔体/水圈的相互作用，或这些变化跟踪挥发性元素丰度在不同的地幔水库参与玄武岩成因？ (ii)水和氯的丰度在多大程度上与其他同位素和微量元素特征相关，表明存在循环洋壳？ (iii)有多少水或氯保留在俯冲洋壳中，并在俯冲引起的脱水后返回到深部地幔？地幔中水和其他挥发性物质的丰度和分布对地幔对流、熔体生成以及地球内部化学和物理演化中涉及的其他基本过程有重大影响。 地球内部与水圈和大气层的相互作用也可能在地质时间尺度上改变地球表面的环境。 目前，地幔中水和其他挥发分的数量和分布受到很差的限制。 目前还不清楚板块形成和后来的俯冲过程是否会导致地球表面水和其他挥发物的净增加或净损失。 这项研究将提供一个更好的了解的丰度和起源的挥发性物质在不同的地幔水库和作用，板块构造和板块俯冲在控制脱气（可能再放气）的地幔随着时间的推移。

This project will examine volatile abundances (water, CO2, Cl, and S) in olivine-hosted melt inclusions from lavas from the Austral Island chain. Previous study of lavas from these islands indicates the involvement of three distinct mantle components, including a component believed to derive from ancient recycled oceanic crust. Volatile element abundance and speciation data will be combined with major and trace element data as well as in situ Pb-isotope data to evaluate several fundamental questions regarding the genesis of these lavas and the nature of their mantle sources. Specific questions that will be addressed include: (i) do variations in Cl concentrations and Cl/K2O ratios in Austral Islands melt inclusions derive from shallow melt/crust or melt/hydrosphere interaction, or do these variations track volatile element abundances in the different mantle reservoirs involved in basalt genesis? (ii) to what extent do water and chlorine abundances correlate with other isotopic and trace element signatures indicative of the presence of recycled oceanic crust? (iii) how much water or chlorine is retained in subducted oceanic crust and returned to the deep mantle after subduction-induced dehydration?The abundance and distribution of water and other volatile species in the mantle has a significant effect on mantle convection, melt generation, and other fundamental processes involved in the chemical and physical evolution of the Earth's interior. Interaction of the Earth's interior with the hydrosphere and atmosphere may also alter the Earth's surface environment on geologic timescales. At present, the amount and distribution of water and other volatiles in the mantle are poorly constrained. It is also unclear whether the processes of plate creation and later subduction result in a net gain or a net loss of water and other volatiles at the Earth's surface. This study will provide a better understanding of the abundance and origin of volatile species in different mantle reservoirs and the role that plate tectonics and plate subduction have played in controlling degassing (and possibly re-gassing) of the mantle over time.