The Importance of the Size and Distribution of Mantle Heterogeneities to the Interpretation of Isotope Ratios and Trace Element Abundances in Basalts

地幔异质性的大小和分布对玄武岩同位素比和微量元素丰度解释的重要性

• 批准号: 1852088
• 负责人: Yan Liang
• 金额: $ 35.74万
• 依托单位: Brown University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-04-15 至 2023-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1852088&HistoricalAwards=false
• 关键词: Importance; Size; Distribution; Mantle; Heterogeneities

Oceanic islands such as Hawaii are formed by volcanic eruptions. Magmas that feed the volcanos are produced by partial melting in the interior of the Earth. Oceanic basalts, which are sampled at oceanic islands and along mid-ocean ridges on the seafloor, provide important clues to understanding the composition of the inaccessible Earth and the processes and time scales of magma generation and transport in the mantle. A fundamental observation in geochemistry is that the source regions of oceanic basalts in the mantle are heterogeneous and consist of chemically and lithologically distinct domains of variable size and distribution. Partial melting of such heterogeneous mantle sources gives rise to a diverse range of basaltic magmas erupted on the surface. The size and distribution of mantle heterogeneities are unknown, but may have played an important role in controlling chemical variations observed in basalts. One of the long-standing problems of geochemistry is the mapping of heterogeneities observed in basalts into the chemical and lithological heterogeneities in the mantle source. Such a mapping is nonlinear and its mathematical expression is unknown. The thesis of this project is to investigate how the size and distribution of mantle heterogeneities affect the isotope ratios and trace element abundances in oceanic basalts. Results from this project will enable geochemists to establish the nonlinear mapping between basalts and their mantle sources. The project would advance STEM education by providing research opportunities for undergraduate students and by developing of a competitive STEM workforce through training of graduate students and postdoc scholar. The primary objectives of this proposed study are (1) to find the functional forms for the nonlinear mapping between basalts and their mantle sources; (2) to develop a framework for understanding and interpreting variations in isotope ratios and trace element abundances in spatially and temporally associated oceanic basalts; and (3) to test the new models through selected case studies where temporal or spatial geochemical data are available. To establish the nonlinear mapping, one needs to know the nature of heterogeneity (chemical vs. lithological, size and distribution), the style of melting (batch vs. fractional), the process of melt migration (channelized vs. grain-scale porous flow), and the extent of chemical disequilibrium between residual minerals and the percolating melt. Time and spatial variables will be added to the widely used melting models in the geochemical literature. These time-dependent melting models will enable geochemists to systematically study the roles of the size and distribution of heterogeneities in the mantle source in controlling the variations of isotope ratios and incompatible trace element abundances in extracted melts. Two-dimensional models will be constructed using the one-dimensional time-dependent melting models. These physically more realistic models will be used to examine variations of Sr-Nd-Hf-Pb isotope and selected incompatible trace element ratios in mid-ocean ridge basalts and ocean island basalts. An important outcome of the proposed work is a set of new interpretation tools to petrologists and geochemists in their studies of spatially and temporally correlated mantle and mantle-derived samples.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

海洋岛（例如夏威夷）是由火山喷发形成的。 饲养火山的岩浆是通过在地球内部部分熔化而产生的。海洋玄武岩是在海洋岛上和海底海脊中采样的，为了解无法接近地球的组成以及地幔中岩浆产生和运输的过程和时间尺度提供了重要的线索。 地球化学的基本观察是，地幔中的海洋玄武岩的来源区域是异质的，由化学和岩性上不同的尺寸和分布的化学和岩性不同的域组成。 这种异质地幔源的部分熔化会导致表面爆发的各种玄武岩岩浆。地幔异质性的大小和分布尚不清楚，但在控制玄武岩中观察到的化学变化中可能起着重要作用。 地球化学的长期问题之一是在玄武岩中观察到的异质性映射到地幔源中的化学和岩性异质性。 这样的映射是非线性的，其数学表达未知。 该项目的论点是研究地幔异质性的大小和分布如何影响海洋玄武岩中的同位素比和痕量元素丰度。 该项目的结果将使地球化学主义者能够在玄武岩及其地幔来源之间建立非线性映射。该项目将通过为本科生提供研究机会，并通过培训研究生和博士后学者来发展竞争性的STEM劳动力，从而提高STEM教育。 这项拟议的研究的主要目标是（1）找到玄武岩及其地幔源之间非线性映射的功能形式； （2）开发一个框架，以理解和解释在空间和时间相关的海洋玄武岩中同位素比和痕量元素丰度的变化； （3）通过选定的案例研究来测试新模型，在这些案例研究中，可以使用时间或空间地球化学数据。 为了建立非线性映射，人们需要了解异质性的性质（化学与岩性，大小和分布），熔化的样式（批次与分数），熔体迁移的过程（通道化与谷物尺度的多孔流）以及残留矿物质和渗透熔体之间的化学不平衡的程度。 时间和空间变量将被添加到地球化学文献中广泛使用的熔融模型中。 这些依赖时间的熔融模型将使地球化学主义者能够系统地研究地幔源中异质性在控制同位素比的变化和提取熔体中不兼容的痕量元素丰度的作用。 二维模型将使用一维时间依赖的熔融模型构建。 这些物理上更现实的模型将用于检查中腹脊和海洋岛玄武岩中SR-ND-HF-PB同位素的变化和选定的不相容的微量元素比率。 拟议工作的一个重要结果是在对空间和时间相关的地幔和地幔衍生的样本的研究中，向岩石学家和地球化学家提供了一系列新的解释工具。这项奖项反映了NSF的法定任务，并通过使用该基金会的智力功能和广泛的影响来评估NSF的法定任务。

项目成果

Calcium diffusion in enstatite, with application to closure temperature of the Ca-in-opx thermometer

顽辉石中的钙扩散，适用于 Ca-in-opx 温度计的闭合温度

• DOI: 10.1016/j.gca.2022.06.018
• 发表时间: 2022
• 期刊: Geochimica et Cosmochimica Acta
• 影响因子: 5
• 作者: Cherniak, D.J.;Liang, Y.
• 通讯作者: Liang, Y.

Mixing Loops, Mixing Envelopes, and Scattered Correlations among Trace Elements and Isotope Ratios Produced by Mixing of Melts Derived from a Spatially and Lithologically Heterogenous Mantle

空间和岩性异质地幔熔体混合产生的混合环、混合包络线以及微量元素和同位素比率之间的分散相关性

• DOI: 10.1093/petrology/egac092
• 发表时间: 2022
• 期刊: Journal of Petrology
• 影响因子: 3.9
• 作者: Liang, Yan

Trace element fractionation and isotope ratio variation during melting of a spatially distributed and lithologically heterogeneous mantle

• DOI: 10.1016/j.epsl.2020.116594
• 发表时间: 2020-12
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: Yan Liang

Importance of permeability and deep channel network on the distribution of melt, fractionation of REE in abyssal peridotites, and U-series disequilibria in basalts beneath mid-ocean ridges: A numerical study using a 2D double-porosity model

渗透率和深水通道网络对熔体分布、深海橄榄岩中稀土元素分馏以及大洋中脊下玄武岩 U 系不平衡的重要性：使用二维双孔隙模型的数值研究

• DOI: 10.1016/j.epsl.2019.115788
• 发表时间: 2019
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: Liu, Boda;Liang, Yan
• 通讯作者: Liang, Yan

Formation of Amphibole‐Bearing Peridotite and Amphibole‐Bearing Pyroxenite Through Hydrous Melt‐Peridotite Reaction and In Situ Crystallization: An Experimental Study

• DOI: 10.1029/2020jb019382
• 发表时间: 2021-03
• 期刊: Journal of Geophysical Research: Solid Earth
• 作者: Chunguang Wang;Yan Liang;Wenliang Xu