Mathematics – Logic
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.u12a..13b&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #U12A-13
Mathematics
Logic
1500 Geomagnetism And Paleomagnetism, 1512 Environmental Magnetism, 1519 Magnetic Mineralogy And Petrology, 1540 Rock And Mineral Magnetism, 1594 Instruments And Techniques
Scientific paper
Magnetic minerals in rocks and sediments are information repositories for past changes in the geological or planetary environment, preserved in the varying composition, concentration, grain size and overall magnetic alignment of the magnetic species: iron oxides, hydroxides, carbonates and sulfides. The creation of the Institute for Rock Magnetism, with the support of the National Science Foundation's Earth Science Division, the Keck Foundation and the University of Minnesota - Twin Cities, has meant that scientists who use paleomagnetism and rock magnetism can have some of their most basic questions answered through cooperative research at the IRM. In the last decade, scientists from two other disciplines -- global environmental change and biomagnetism -- have also utilized the IRM for controlled experiments on target minerals, sometimes as small as 5 nm, to interpret in a more quantitative manner the amplitudes of past variations. Of all the instruments made available to the magnetics community by the IRM, e.g., high and low field magnetometers, particle size analyzers, M”ssbauer spectrometers and magneto-optic and magnetic force microscopes, it is the SQUID susceptometers (operating at temperatures down to 1.5K and magnetic fields from zero to 5 Tesla) that have made the most impact on the science. In-house researchers and NSF/EAR-supported visiting fellows have made a number of discoveries based on new fundamental knowledge of low temperature magnetism of the following 8 minerals: (titano)magnetite, hematite, goethite, lepidocrocite, ferrihydrite, siderite, rhodochrocite and pyrrhotite. For a significant number of U.S. and international geologists and geophysicists, thermal demagnetization of low temperature (~10-20K) magnetizations has now become the most widely-used non-destructive technique for recognition and estimation of (a) magnetite in natural sediments, (b) glacial/interglacial climate change records in worldwide loess deposits and (c) paleoredox histories in lake and marine sediments. Sophisticated low-temperature treatments applied to room-temperature magnetizations have led to understanding microstructural control of magnetic remanence, particularly in magnetite and hematite. Some resulting new techniques include paleointensities from meteorites, environment-controlled growth mechanisms in nanophase (~5 nm) iron oxides and hydroxides, and precise location and dating of cold/warm climate transitions in loess deposits. The unique advantage of such high-speed, high-sensitivity techniques is the ability to study as-is natural samples with no pre-treatment or magnetic separation, resulting in rapid regional verification of the data.
Banerjee Sanjay K.
Jackson James M.
Marvin James A.
Moskowitz Bruce M.
Solheid Peter A.
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