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Jackson M, Swanson-Hysell NL. Rock magnetism of remagnetized carbonate rocks: another look. ACTA ACUST UNITED AC 2012. [DOI: 10.1144/sp371.3] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
AbstractAuthigenic formation of fine-grained magnetite is responsible for widespread chemical remagnetization of many carbonate rocks. Authigenic magnetite grains, dominantly in the superparamagnetic and stable single-domain size range, also give rise to distinctive rock-magnetic properties, now commonly used as a ‘fingerprint’ of remagnetization. We re-examine the basis of this association in terms of magnetic mineralogy and particle-size distribution in remagnetized carbonates having these characteristic rock-magnetic properties, including ‘wasp-waisted’ hysteresis loops, high ratios of anhysteretic remanence to saturation remanence and frequency-dependent susceptibility. New measurements on samples from the Helderberg Group allow us to quantify the proportions of superparamagnetic, stable single-domain and larger grains, and to evaluate the mineralogical composition of the remanence carriers. The dominant magnetic phase is magnetite-like, with sufficient impurity to completely suppress the Verwey transition. Particle sizes are extremely fine: approximately 75% of the total magnetite content is superparamagnetic at room temperature and almost all of the rest is stable single-domain. Although it has been proposed that the single-domain magnetite in these remagnetized carbonates lacks shape anisotropy (and is therefore controlled by cubic magnetocrystalline anisotropy), we have found strong experimental evidence that cubic anisotropy is not an important underlying factor in the rock-magnetic signature of chemical remagnetization.
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Affiliation(s)
- Mike Jackson
- Institute for Rock Magnetism, Winchell School of Earth Sciences, University of Minnesota, Minnesota, US
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Dunlop DJ. Theory and application of the Day plot (Mrs/MsversusHcr/Hc) 1. Theoretical curves and tests using titanomagnetite data. ACTA ACUST UNITED AC 2002. [DOI: 10.1029/2001jb000486] [Citation(s) in RCA: 664] [Impact Index Per Article: 30.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Dunlop DJ. Theory and application of the Day plot (Mrs/MsversusHcr/Hc) 2. Application to data for rocks, sediments, and soils. ACTA ACUST UNITED AC 2002. [DOI: 10.1029/2001jb000487] [Citation(s) in RCA: 309] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Newell AJ, Merrill RT. Size dependence of hysteresis properties of small pseudo-single-domain grains. ACTA ACUST UNITED AC 2000. [DOI: 10.1029/2000jb900122] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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