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.
