Magnetite (U-Th-Sm)/He Geochronology - A Novel Technique for Dating Continental and Oceanic Basalts

知识价值。大陆和海洋玄武质喷发岩是地球表面最常见的火山岩类型，其时空演化对认识板块构造、地幔熔融过程、古地磁、大陆洪水玄武岩省等具有重要意义。同时，玄武岩，尤其是暗质和蚀变的玄武岩，通常很难确定其年代。磁铁矿（Fe3O4）在几乎所有类型的挤压岩中都有发现，在玄武岩到中等火山岩类型中也很常见。提出了发展和校准磁铁矿(U-Th-[Sm])/He定年作为可靠测定玄武岩年龄的新技术。我们预计，这种方法和拟议案例研究的结果应该引起对大陆和海洋领域感兴趣的地球科学界的大量不同部分的极大兴趣。在一项可行性研究中，开发了磁铁矿(U-Th-[Sm])/He定年的分析方法，并证明了其在玄武岩熔岩定年方面的潜力，而其他技术可能无法提供有意义的结果。本项目将严格发展和校准磁铁矿的年代，并探索其在大陆和海洋玄武岩中的地质应用。本研究的具体目标是：(1)研究磁铁矿中的4He和3He扩散动力学，(2)改进分析技术以提高磁铁矿(U-Th-[Sm])/He年代学的精度和准确性，(3)对Steens-Columbia河玄武岩进行磁铁矿(U-Th-[Sm])/He定年案例研究，以及(4)将磁铁矿(U-Th-[Sm])/He定年应用于N皇海山链（IODP Leg 197）和Ninetyeast Ridge （IODP Leg 183）的海洋玄武岩。更广泛的影响。拟议的项目评估了一种新的地球计时器，用于目前众所周知难以或不可能确定日期的样品，特别是在处理隐晶岩和/或蚀变玄武岩时。这将代表着方法论上的重大进步，并将为其他科学家提供一种新技术。这项研究将支持一名女性研究生研究助理，并让一名本科生参与研究的某些方面。该项目将涉及堪萨斯大学小组与麻省理工学院和伯克利地质年代学中心的科学家之间的合作。PI通过与波多黎各马亚圭斯大学（UPRM）的KU地质学合作多样性倡议，努力让少数民族学生参与同位素地球化学。这一多样性倡议鼓励少数民族学生从事本科暑期研究和研究生工作。

Intellectual merit. Continental and oceanic basaltic extrusive rocks are the most common volcanic rock types on the earth's surface and their temporal and spatial evolution are critical for the understanding of plate tectonics, mantle melting processes, paleomagnetism, continental flood basalt provinces, etc. At the same time, basaltic rocks, especially when aphanitic and altered, are often difficult to date. Magnetite (Fe3O4) is found in nearly all types of extrusive rocks and common in basaltic to intermediate volcanic rock types. It is proposed to develop and calibrate magnetite (U-Th-[Sm])/He dating as a novel technique for reliably determining ages of basaltic rocks. We anticipate that this approach and results from the proposed case studies should be of significant interest to a large and diverse portion of the geosciences community interested in the continental and oceanic realm. In a feasibility study, analytical procedures were developed for magnetite (U-Th-[Sm])/He dating and its potential demonstrated in reliably dating basaltic lavas where other techniques might not provide meaningful results. This project will rigorously develop and calibrate the dating of magnetite and explore its geological application to both continental and oceanic basaltic rocks. Specific objectives of this study are to (1) investigate 4He and 3He diffusion kinetics in magnetite, (2) refine analytical techniques to improve precision and accuracy of magnetite (U-Th-[Sm])/He geochronology, (3) conduct a magnetite (U-Th-[Sm])/He dating case study on the Steens-Columbia River basalts, and (4) apply magnetite (U-Th-[Sm])/He date to oceanic basalts from the N Emperor Seamount chain (IODP Leg 197) and Ninetyeast Ridge (IODP Leg 183).Broader impacts. The proposed project evaluate a new geochronometer for use with samples that are notoriously difficult or impossible to date at present, especially when dealing with aphanitic and/or altered basalt. This will represent a considerable methodological advance and will offer a new technique for other scientists to utilize. The study will support a female graduate research assistant and involve an undergraduate student in some aspects of the research. The project will involve collaboration between the Kansas U. group and with scientists from MIT and Berkeley Geochronology Center. The PI strives to involve minority students in isotope geochemistry through participation in a KU Geology collaborative diversity initiative with the University of Puerto Rico Mayaguez (UPRM). This diversity initiative encourages minority students to pursue undergraduate summer research and graduate work.