Investigation of Fe Isotope Fractionation During Magmatic Differentiation at the Skaergaard Intrusion

斯卡尔加德岩体岩浆分异过程中铁同位素分馏的研究

• 批准号: 1430219
• 负责人: Adriana Heimann Rios
• 金额: $ 25.71万
• 依托单位: East Carolina University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-09-01 至 2018-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1430219&HistoricalAwards=false
• 关键词: Investigation; Fe; Isotope; Fractionation; During

Magma evolution is responsible for the wide range of igneous rocks observed on Earth as well as their varied chemical compositions and the genesis of associated economic mineral deposits. Of fundamental importance for understanding magmatic evolution and planetary formation processes are detailed geochemical studies of large simple igneous systems. Layered mafic-ultramafic igneous complexes are not only useful for understanding magmatic differentiation processes but also important economically for being the main source of platinum group elements, Cr, Ni, Cu, and Fe ore deposits. Iron isotope studies can help unravel the formation processes of these igneous complexes as well as their mineral deposits because the different isotopes of Fe can potentially partition into different phases during diverse processes, including crystallization of minerals from the melt, assimilation of country rocks, and reactions between rocks and late-stage hydrothermal fluids. Within individual crystals Fe isotopes can also diffuse through various minerals at different rates and may also reflect equilibrium (magmatic) or non-equilibrium (kinetic) processes. Improvements in the precision of Fe stable isotope measurements of bulk rocks and minerals by multi collector inductively coupled plasma mass spectrometry (MC-ICP-MS) show that significant variations exist in high-temperature mafic and ultramafic terrestrial crustal and mantle igneous rocks, lunar mafic rocks, and meteorites. These findings promise success for understanding magmatic differentiation and planetary formation processes. However, the current knowledge of Fe isotope compositions of individual minerals and fractionations among them in these rocks is still limited, and the causes, mechanisms, and implications of Fe isotope fractionations in high-temperature terrestrial and extraterrestrial igneous systems are still poorly understood. Only a very limited number of igneous intrusions have been investigated in detail with Fe isotopes. In addition, in situ Fe isotope measurements of individual minerals in extraterrestrial rocks are not available and only very few exist for terrestrial rocks. This means that Fe isotope compositions previously measured in bulk minerals may well be, in many cases, an average of the complex compositions recorded during crystal growth, diffusion, or late-stage hydrothermal alteration. This project will determine the extents, causes, and mechanisms of Fe isotope fractionations in a simple high-temperature magmatic system combining Fe and O isotope analysis of bulk-rocks and minerals with high-spatial resolution in situ Fe and O isotope analysis of minerals by femtosecond laser ablation (fs-LA) MC-ICP-MS and secondary ion mass spectrometry (SIMS), respectively, in the mafic-ultramafic layered intrusion of Skaergaard, Greenland, the most studied intrusive complex on Earth. This intrusion exemplifies a highly differentiated magma chamber originated from a single, large, magma body that underwent extensive, closed-system evolution through fractional crystallization that later underwent hydrothermal alteration. The results of this research will help understand the processes of formation of mafic-ultramafic layered intrusions and their host magmatic mineral deposits and has implications for understanding planetary differentiation processes.The emphasis of this project is on systematic, high resolution, inter-mineral Fe isotope fractionations and in situ intra-mineral Fe isotope compositions (by fs-LA-MC-ICP-MS). Because fs-LA-MC-ICP-MS is a new technique in geochemistry, this research will help develop the method that may ultimately benefit the broader geoscience community. Detailed bulk-rock and mineral Fe and O isotope compositions combined with in situ Fe isotope compositions, mineral chemistry, O isotope cooling temperatures, bulk-rock major and trace element compositions, and modeling will produce the most comprehensive and detailed study of a single large igneous intrusion. Oxygen isotope compositions will help discern high-temperature magmatic Fe isotope compositions (equilibrium) from kinetic and late-stage hydrothermal effects. All these data together will help identify the origin of the measured fractionations (fractional crystallization, chemical diffusion, thermal diffusion, late-stage hydrothermal alteration). The inter-mineral Fe isotope fractionation factors as a function of temperature calculated for Skaergaard will be useful for understanding those in other terrestrial igneous systems, lunar and Martian rocks, and other planetary bodies. Because large samples are hard to obtain from meteorites, this study will provide much needed information to determine the best approach for extraterrestrial sample studies. The results of this work will improve our understanding of large-scale evolution of Fe isotopes at the intrusion level as well as small scale, Fe isotope heterogeneities within crystals. This project combines the expertise of mineralogy, petrology, economic geology, geochemistry, and Fe and O isotope geochemistry of the PI and collaborators from the University of Wisconsin-Madison. This project will support an early career female scientist, fund two M.S. theses and undergraduate student researchers, and support the development of the physical infrastructure for research on state-of-the-art high-temperature isotope geochemistry at East Carolina University. This collaboration will also provide graduate and undergraduate students at ECU the experience of working with state-of-the-art analytical facilities at UW-Madison and interact with top leaders in geochemistry.

岩浆演化是地球上所观察到的各种火成岩及其不同化学成分和相关经济矿床成因的原因。 对于了解岩浆演化和行星形成过程至关重要的是对大型简单火成岩系统进行详细的地球化学研究。 层状镁铁质-超镁铁质火成杂岩不仅有助于了解岩浆分异过程，而且是铂族元素、Cr、Ni、Cu和Fe矿床的主要来源，具有重要的经济意义。 铁同位素研究有助于揭示这些火成杂岩及其矿床的形成过程，因为不同的铁同位素可能在不同的过程中分成不同的相，包括矿物从熔体中结晶，围岩的同化，以及岩石与后期热液流体之间的反应。 在单个晶体中，Fe同位素也可以以不同的速率扩散到各种矿物中，也可以反映平衡（岩浆）或非平衡（动力学）过程。 用多接收电感耦合等离子体质谱（MC-ICP-MS）测定岩石和矿物中Fe稳定同位素的精度得到了提高。结果表明，高温镁铁质和超镁铁质地壳和地幔火成岩、月面镁铁质岩石和陨石中存在显著的变化。 这些发现有望成功理解岩浆分异和行星形成过程。 然而，目前对这些岩石中单个矿物的Fe同位素组成及其分馏的认识仍然有限，并且对高温陆地和地外火成岩系统中Fe同位素分馏的原因、机制和意义仍然知之甚少。 只有非常有限的几个火成岩侵入体进行了详细的铁同位素研究。 此外，在地外岩石中的单个矿物的原位铁同位素测量是不可用的，只有极少数存在的陆地岩石。 这意味着，铁同位素组成先前测量的散装矿物，在许多情况下，在晶体生长，扩散，或后期热液蚀变过程中记录的复杂组合物的平均值。 本项目将确定一个简单的高温岩浆系统中Fe同位素分馏的程度、原因和机制，结合大块岩石和矿物的Fe和O同位素分析以及分别通过飞秒激光烧蚀（fs-LA）MC-ICP-MS和二次离子质谱法（西姆斯）对Skaergaard镁铁质-超镁铁质层状侵入体进行的矿物的高空间分辨率原位Fe和O同位素分析，格陵兰岛，地球上研究最多的侵入复合体。 这一侵入体证实了一个高度分化的岩浆房，该岩浆房起源于一个单一的大型岩浆体，该岩浆体通过分离结晶经历了广泛的封闭系统演化，后来又经历了热液蚀变。 本研究的重点是系统的、高分辨率的矿物间Fe同位素分馏和原位矿物内Fe同位素组成（fs-LA-MC-ICP-MS）。 由于fs-LA-MC-ICP-MS是地球化学中的一项新技术，因此这项研究将有助于开发最终可能使更广泛的地球科学界受益的方法。 详细的大块岩石和矿物Fe和O同位素组成结合原位Fe同位素组成，矿物化学，O同位素冷却温度，大块岩石的主要和微量元素组成，和建模将产生最全面和详细的研究一个单一的大型火成岩侵入。 氧同位素组成将有助于区分高温岩浆铁同位素组成（平衡）的动力学和后期热液效应。 所有这些数据一起将有助于确定所测量的分馏（结晶分离，化学扩散，热扩散，后期热液蚀变）的起源。 矿物间Fe同位素分馏因子作为温度的函数计算Skaergaard将是有用的，了解那些在其他陆地火成岩系统，月球和火星岩石，和其他行星体。 由于很难从陨石中获得大样本，这项研究将提供急需的信息，以确定外星样本研究的最佳方法。 这项工作的结果将提高我们的理解，大规模的演化Fe同位素的侵入水平，以及小规模，晶体内的Fe同位素的不均匀性。该项目结合了PI和威斯康星大学麦迪逊分校合作者的矿物学，岩石学，经济地质学，地球化学以及Fe和O同位素地球化学的专业知识。 该项目将支持一名早期职业女性科学家，资助两名硕士。该项目为研究人员和本科生研究人员提供了大量的技术支持，并支持东卡罗莱纳大学发展最先进的高温同位素地球化学研究的物理基础设施。 这种合作还将提供ECU的研究生和本科生与威斯康星大学麦迪逊分校最先进的分析设施合作的经验，并与地球化学领域的顶级领导人互动。

项目成果

SIMS matrix effects in oxygen isotope analysis of olivine and pyroxene: Application to Acfer 094 chondrite chondrules and reconsideration of the primitive chondrule minerals (PCM) line

• DOI: 10.1016/j.chemgeo.2022.121016
• 发表时间: 2022-07
• 期刊: Chemical Geology
• 影响因子: 3.9
• 作者: Mingming Zhang;K. Fukuda;M. Spicuzza;G. Siron;A. Heimann;Alexander Hammerstrom;N. Kita;T. Ushikubo;J. Valley