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

智力上的优点。大陆和大洋玄武岩是地球表面最常见的火山岩类型，它们的时空演化对于了解板块构造、地幔熔融过程、古地磁、大陆泛滥玄武岩省等具有重要意义。同时，玄武岩，特别是玄武岩，尤其是隐形玄武岩和蚀变岩，往往难以确定年代。磁铁矿(Fe3O4)几乎存在于所有类型的喷出岩中，并常见于玄武岩至中间火山岩类型。提出开发和标定磁铁矿(U-Th-[Sm])/He测年技术，作为一种可靠测定玄武岩年龄的新技术。我们预计，对大陆和海洋领域感兴趣的地球科学界的很大一部分人应该会对这种方法和拟议的案例研究的结果产生重大兴趣。在一项可行性研究中，开发了磁铁矿(U-Th-[Sm])/He测年的分析程序，并在其他技术可能无法提供有意义结果的玄武岩熔岩可靠测年中展示了其潜力。该项目将严格开发和标定磁铁矿的年龄，并探索其在大陆和海洋玄武岩中的地质应用。这项研究的具体目标是：(1)研究4He和3He在磁铁矿中的扩散动力学；(2)改进分析技术以提高磁铁矿(U-Th-[Sm])/He年代学的精密度和准确度；(3)对Steens-Columbia River玄武岩进行磁铁矿(U-Th-[Sm])/He定年研究；(4)将磁铁矿(U-Th-[Sm])/He年龄应用于N帝海山链(IODP腿197)和第九酵母岭(IODP腿183)的大洋玄武岩。拟议的项目评估了一种新的地质计时仪，用于目前出了名的难以测年或不可能测年的样品，特别是在处理隐形玄武岩和/或蚀变玄武岩时。这将代表着方法上的巨大进步，并将为其他科学家提供一种新的技术来使用。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团队以及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。国际和平研究所通过与波多黎各大学马亚圭斯大学(UPRM)共同参与密歇根大学地质学合作多样性倡议，努力让少数族裔学生参与同位素地球化学。这一多样性倡议鼓励少数族裔学生进行本科生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.