This grant supports a three year continuation of funding for the Institute for Rock Magnetism (IRM) at the University of Minnesota. The goals of the IRM include: 1) providing the geoscience research community with access to a full suite of sensitive instrumentation for detailed study of magnetic properties of natural materials; 2) providing visiting scholars with the support necessary to use the facilities effectively, including technical, educational, and logistical components of support; 3) adapting methods and techniques from physics and materials science, as well as developing new methods, for using magnetic measurement data to characterize complex natural samples and to address questions of specific interest to geoscientists; and; 4) serving as a catalyst in widening and improving the applications of magnetic analysis in geological and biological studies, by holding workshops and conferences, and by maintaining active (and separately funded) research programs in those areas. Research facilitated by the analytical and technical capabilities of the IRM includes high resolution studies of variability in the intensity of the Earth's magnetic field in order to elucidate fundamental questions surrounding the origin of the geodynamo, characterization of the properties of microbial nanophase magnetic minerals, and fundamental studies of the origin of magnetization in minerals and the behavior of magnetic minerals in response to environmental perturbations in temperature and applied magnetic fields. The IRM supports the training of graduate and postdoctoral students in state-of-the-art rock and paleomagnetic analysis techniques and facilitates international collaborations through the Visiting Fellows program and a biennial conference series.
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The Institute for Rock Magnetism (IRM) serves as a national center for research on Earth (and extraterrestrial) materials using magnetic instrumentation and techniques of analysis. At this facility, an advanced set of sensitive instruments is maintained and made available to researchers for studies aimed at mining the information stored in the magnetic characteristics and the magnetic memory of the iron-bearing minerals in natural samples. Research by IRM-resident scientists is complemented by that of Visiting Fellows, selected through a competitive proposal process from the global geoscience community. More than 50 Visiting Fellows have worked at the IRM during the past three-year grant period, on projects involving paleoclimate and paleoenvironmental research, paleogeographic reconstruction of the past locations of the continents and oceanic tectonic plates, and the history of the Earth’s magnetic field. Some of the IRM’s key recent research findings include: Nanostructures in iron-titanium (Fe-Ti) oxide minerals formed by slow cooling over millions of years can record an unusually strong and stable magnetization. This newly-discovered interfacial magnetic ordering, "lamellar magnetism," plays an important role in generating some major magnetic anomalies measured above Earth’s surface, and it may contribute to the satellite-measured anomalies on Mars. Fe-Ti oxide minerals may form by exsolution ("unmixing") of iron silicate minerals such as pyroxene, and in the process they capture high-fidelity records of the orientation and strength of geomagnetic field. Within the silicate host mineral, these tiny magnetic inclusions are shielded against chemical alteration by hydrothermal fluids and weathering, factors which often degrade the paleomagnetic signal in rocks. In the example shown in Image 1, "A" shows the surface topography of a polished rock surface, with mineral boundaries discernible. In "B" the magnetic structure of the Fe-Ti oxide grain is imaged by means of the magnetic forces exerted on the scanning probe by the sample. "C" shows the magnetic structure inferred (cpx is clinopyroxene). Understanding how such magnetic "domain" structures form and how they are affected by temperature, pressure and time are fundamental aspects of the effort to reconstruct the past variations in the geomagnetic field through magnetic measurements of rocks and sediments. In the glassy crusts of submarine basaltic lava flows produced at mid-ocean ridges, small (less than 1 micrometer) iron-titanium oxide particles crystallize at high temperatures on cooling from a melt, so the glasses carry a primary magnetization. This finding confirms that submarine basaltic glass can be used to reconstruct reliable records of the variations in the strength of the geomagnetic field for the last 200,000 years. High-sensitivity experimental magnetic techniques and theoretical models can now be used to identify minute concentrations of single magnetic domain particles (<0.1 micrometers) in sediments, some of which are produced by various types of microorganisms. Identification of biologically-produced magnetic iron phases in whole rock samples will allow scientists to study the environmental influences on iron biomineralization and to quantify biomagnetic mineral populations in the geologic record.
