Institute for Rock Magnetism (IRM)
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The Institute for Rock Magnetism (IRM) was established in the fall of 1990 as a National Multi-User Facility whose core mission is to serve the greater geomagnetic community by providing free-of-charge access to state-of-the-art facilities and technical expertise, and by encouraging visiting researchers in their studies of important new topics in rock magnetism and related interdisciplinary fields. See the website at http://www.irm.umn.edu/IRM.
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Browsing Institute for Rock Magnetism (IRM) by Subject "rock magnetism"
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Item The effect of low‐temperature hydrothermal alteration on the remanent magnetization of synthetic titanomagnetites: A case for acquisition of chemical remanent magnetization(Journal of Geophysical Research (American Geophysical Union), 1991) Kelso, Paul; Banerjee, Subir; Worm, HorstItem The rock magnetic fingerprint of chemical remagnetization in midcontinental Paleozoic carbonates(Geophysical Research Letters (American Geophysical Union), 1992) Jackson, Mike; Sun, Wei-wei; Craddock, JohnResults of a paleomagnetic and rock magnetic survey of Paleozoic carbonates from 39 sites in the midcontinental U.S. show that many of these sites carry a stable remanence of apparent Permian age. Many of these remagnetized sites also have relatively high anhysteretic susceptibilities, and higher saturation remanence than most of the sites where the late Paleozoic remanence is absent. However the correlation between late Paleozoic remanence and high anhysteretic susceptibility or high saturation remanence is imperfect. The most diagnostic rock magnetic parameter for recognizing remagnetized sites is a ratio of anhysteretic remanence/saturation remanence exceeding 10%. We have found high ratios in almost all remagnetized sites, but in very few sites where the Late Paleozoic remanence is absent. The high ratios reflect the presence of a significant fraction of extremely fine-grained magnetite (a few tens of nanometers), spanning the superparamagnetic-single domain threshhold.Item Rock magnetic properties of the Arunta Block, Central Australia, and their implication for the interpretation of long-wavelength magnetic anomalies(Journal of Geophysical Research (American Geophysical Union), 1993) Kelso, Paul; Banerjee, Subir; Teyssier, ChristianRock magnetic and petrologic studies of a suite of deep crustal rocks from the Arunta Block of Central Australia reveal that the granulite grade rocks are in general much more magnetic than the amphibolite grade samples irrespective of bulk rock composition. The dominant magnetic mineral in all samples is relatively pure magnetite as determined from thermomagnetic and electron microprobe analysis. The bulk magnetic properties are typical of pseudo-single-domain to multidomain size material. The samples from our study have very large remanences compared to previous crustal magnetic studies, with the granulites having a median natural remanent magnetization of 4.1 A/m and Koenigsberger ratio of 7.2. These remanences are relatively resistant to thermal demagnetization, with nearly 50% of the magnetization remaining after 400°C demagnetization. Thus remanence may contribute significantly to the observed magnetic anomalies, including long-wavelength magnetic anomalies, the source of which resides at depth and therefore at elevated temperature, where a thermoviscous remanent magnetization along the present-day field is likely to dominate. The magnetic susceptibilities of the samples are only capable of producing a magnetization of less than 1 A/m in the 0.05 mT present-day field of Central Australia. Susceptibility is nearly constant with temperature to within 30°C of the Curie temperature where it decreases rapidly, i.e., there is no significant Hopkinson peak. The granulite samples from this study have magnetizations, both remanent and induced components, that are large enough to account for most long-wavelength magnetic anomalies if they are juxtaposed with relatively nonmagnetic rocks, similar to the high-grade rocks in the Canadian Shield.Item Rock magnetism of remagnetized Paleozoic carbonates: low-temperature behavior and susceptibility characteristics(Journal of Geophysical Research (American Geophysical Union), 1993) Jackson, Mike; Rochette, Pierre; Fillion, Gerard; Banerjee, Subir; Marvin, James