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。 对大型简单火成岩系统的详细地球化学研究对于理解岩浆演化和行星形成过程至关重要。 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，而且作为铂族元素、铬、镍、铜和铁矿床的主要来源也具有重要的经济意义。 铁同位素研究可以帮助揭示这些火成杂岩及其矿床的形成过程，因为铁的不同同位素可能在不同的过程中分成不同的相，包括熔体中矿物的结晶、围岩的同化和反应岩石和晚期热液之间。 在单个晶体内，铁同位素还可以以不同的速率扩散通过各种矿物，并且还可以反映平衡（岩浆）或非平衡（动力学）过程。 通过多接收器电感耦合等离子体质谱 (MC-ICP-MS) 对大块岩石和矿物的 Fe 稳定同位素测量精度的提高表明，高温镁铁质和超镁铁质的陆地地壳和地幔火成岩、月球镁铁质存在显着变化岩石、陨石。 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铁同位素组成及其分馏的了解仍然有限，并且对高温陆地和地外火成岩系统中铁同位素分馏的原因、机制和影响仍然知之甚少。 仅用铁同位素详细研究了非常有限数量的火成岩侵入体。 此外，无法对地外岩石中的单个矿物进行原位铁同位素测量，并且对于陆地岩石而言，也只有很少的铁同位素测量。 这意味着，在许多情况下，先前在散装矿物中测量的铁同位素组成很可能是晶体生长、扩散或后期热液蚀变过程中记录的复杂组成的平均值。 该项目将结合大块岩石和矿物的铁和氧同位素分析以及矿物的高空间分辨率原位铁和氧同位素分析，确定简单高温岩浆系统中铁同位素分馏的范围、原因和机制。飞秒激光烧蚀 (fs-LA) MC-ICP-MS 和二次离子质谱 (SIMS) 分别用于镁铁质-超镁铁质层状侵入格陵兰岛斯卡尔加德，地球上研究最多的侵入体综合体。 这种侵入例证了一个高度分化的岩浆房，它起源于一个单一的、大型的岩浆体，该岩浆体通过分步结晶经历了广泛的、封闭的系统演化，随后又经历了热液蚀变。 这项研究的结果将有助于了解镁铁质-超镁铁质层状侵入体及其宿主岩浆矿床的形成过程，并对了解行星分异过程具有重要意义。该项目的重点是系统、高分辨率、矿物间铁同位素分馏和原位矿物内 Fe 同位素组成（通过 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。 详细的块体岩石和矿物 Fe 和 O 同位素成分与原位 Fe 同位素成分、矿物化学、O 同位素冷却温度、块体岩石主要和微量元素成分以及建模相结合，将对单个大型岩石进行最全面和详细的研究。火成岩侵入。 氧同位素组成将有助于从动力学和后期热液效应中辨别高温岩浆铁同位素组成（平衡）。 所有这些数据一起将有助于确定测量的分馏的起源（分馏结晶、化学扩散、热扩散、后期热液蚀变）。 为斯卡尔加德计算的矿物间铁同位素分馏因子作为温度的函数将有助于理解其他陆地火成岩系统、月球和火星岩石以及其他行星体中的矿物间铁同位素分馏因子。 由于很难从陨石中获得大量样本，因此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对侵入水平上铁同位素大规模演化以及晶体内小规模铁同位素异质性的理解。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、地球化学以及铁和氧同位素地球化学方面的专业知识。 该项目将支持一名早期职业女性科学家，资助两名硕士学位。论文和本科生研究人员，并支持东卡罗来纳大学最先进的高温同位素地球化学研究的物理基础设施的开发。 此次合作还将为 ECU 的研究生和本科生提供使用威斯康辛大学麦迪逊分校最先进的分析设施并与地球化学领域的顶尖领导者互动的经验。

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