Near-fractional Melting of Pyroxenite: Experimental Investigations and Applications to Basalt Petrogenesis

辉石岩的近分馏熔融：玄武岩成因实验研究及其应用

• 批准号: 1551442
• 负责人: Sarah Lambart
• 金额: $ 15.36万
• 依托单位: University of California-Davis
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-06-01 至 2018-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1551442&HistoricalAwards=false
• 关键词: Near; fractional; Melting; Pyroxenite; Experimental

The rocks that make up Earth's crust are subject to a cycle of life - new crust is formed at divergent plate boundaries (spreading centers) via the melting of the mantle (material beneath the crust) and transport of magma to the surface, while old crust sinks back into the mantle at convergent plate boundaries. Specifically, the return of oceanic crust to the mantle creates chemical and mineralogical heterogeneities (mixtures of olivine-rich and pyroxene-rich lithologies) that can lead to complex melting behavior when this material rises again beneath spreading centers and in mantle plumes. The abundance and time scales of crustal recycling are important aspects of the plate tectonic cycle, but difficult to constrain based solely on the petrology and geochemistry of crustal rocks. Quantitative modeling requires knowledge of melting behavior of different rock types. The goal of this research is to obtain new high quality experimental data on the melting of pyroxenite, which represents one the most important rock types that are recycled into the mantle. Experiments will be performed at conditions found in the mantle where temperatures are thousands of degrees hotter and pressures tens of thousands of times greater than found at the Earth's surface. The results obtained will be integrated into forward models of melting of heterogeneous mantle that simulate the dynamic processes operating beneath the world's spreading centers and in mantle plumes. The primary objective of this project is to understand the effect of near-fractional melting of pyroxenites, to better quantify the role of pyroxenite in basalt genesis. The experimental approach will consist of performing incremental melting experiments, with increments of melt fraction less than 5 wt. % at each stage, on three different compositions previously investigated by batch melting experiments. The selected compositions span the likely compositional range of pyroxenite lithologies in the mantle. Melt composition at each temperature increment will be determined with the microdike technique and used to define new melting parameterizations that can be used to model near-fractional melting and integrate them into forward models of melting of heterogeneous mantle. NiO and MnO proxies used to determine the pyroxenite contribution in typical basaltic magmas and their source regions will be recalibrated based on the experimental results. Because melt extraction during generation of MORB and ocean island basalts is likely to occur via near fractional melting rather than batch melting, these new calibrations will allow us to better quantify the proportion of pyroxenite in the mantle source of the most abundant magmas on Earth.

构成地壳的岩石经历了一个生命周期--新的地壳通过地幔（地壳下的物质）的熔化和岩浆向地表的输送在分散的板块边界（扩张中心）形成，而旧的地壳在会聚的板块边界处沉入地幔。 具体来说，洋壳向地幔的回归造成了化学和矿物学的不均匀性（富含橄榄石和辉石的岩石的混合物），当这种物质在扩张中心和地幔柱下再次上升时，会导致复杂的熔融行为。 地壳再循环的丰度和时间尺度是板块构造旋回的重要方面，但很难仅根据地壳岩石学和地球化学来约束。 定量建模需要了解不同岩石类型的熔融行为。 本研究的目的是获得新的高质量的实验数据的熔融辉石岩，这是最重要的岩石类型之一，是再循环到地幔。 实验将在地幔中发现的条件下进行，那里的温度比地球表面高数千度，压力比地球表面大数万倍。所获得的结果将被整合到非均匀地幔熔化的正演模型中，该模型模拟了在世界扩张中心和地幔柱下运行的动态过程。 该项目的主要目的是了解辉石岩的近分熔作用，以更好地量化辉石岩在玄武岩成因中的作用。实验方法将包括进行增量熔融实验，其中熔融分数的增量小于5 wt. %，在每个阶段，对三个不同的组合物先前研究的分批熔融实验。所选的组合物涵盖了地幔中辉石岩岩性的可能组成范围。每个温度增量下的熔体成分将使用微堤技术确定，并用于定义新的熔化参数化，这些参数化可用于模拟近部分熔化并将其整合到非均质地幔熔化的正演模型中。本文将根据实验结果重新标定用于确定辉石岩在典型玄武岩岩浆及其源区中贡献的NiO和MnO指标。由于熔融提取过程中产生的MORB和洋岛玄武岩很可能发生通过附近的部分熔融，而不是批量熔融，这些新的校准将使我们能够更好地量化的比例辉石岩在地幔中最丰富的岩浆源在地球上。

项目成果

No direct contribution of recycled crust in Icelandic basalts

• DOI: 10.7185/geochemlet.1728
• 发表时间: 2017-07
• 作者: S. Lambart