Comparison of magnetic hysteresis parameters of unremagnetized and remagnetized limestones

Abstract

For white magnetite‐bearing Mesozoic pelagic limestones from Italy which carry a “primary” magnetization, the values of Mrs/Ms and Hcr/Hc generally lie in the pseudo‐single domain (PSD) field of the Day et al. (1977) plot. The logarithmic plot of Mrs/Ms against Hcr/Hc gives a straight line (R = 0.814) with slope and intercept close to the empirical mixing line of Parry (1982) for single domain (SD) and multidomain (MD) magnetite. For one of the white pelagic limestone formations (Maiolica Formation), samples with hysteresis ratios closer to the MD field display increased paramagnetic susceptibility and are from the upper part of the formation characterized by increased detrital clay. We therefore associate the increased MD magnetite with increased detrital influx. For pinkish and reddish varieties of the Italian pelagic limestones, the presence of hematite is manifest by high saturation fields, a wide range of Hcr/Hc, and “wasp‐waisted” hysteresis loops attributed to the mixing of magnetite and high‐coercivity authigenic hematite. The hysteresis ratios for a collection of Paleozoic and Mesozoic remagnetized magnetite‐bearing limestones from Britain, Nevada, Alaska and the Appalachians lie mainly outside the PSD field and appear to follow a power law trend. Following Jackson et al. (1993), the high values of Hcr/Hc and the characteristically “wasp‐waisted” hysteresis loops can be interpreted in terms of a fine‐grained subspherical high‐coercivity SD magnetite mixed with a high proportion of superparamagnetic magnetite. The slope and intercept of the power law relationship for Mrs/Ms and Hcr/Hc in the remagnetized limestones are distinct from those observed for the Italian limestones, and may provide a means of fingerprinting magnetite of “primary” as opposed to diagenetic origin.

Associations between burial diagenesis of smectite, chemical remagnetization, and magnetite authigenesis in the Vocontian trough, SE France

“…The ratios therefore probably do not represent true PSD grains but rather a mix of sizes. The samples from Berrias fall approximately along the line on a log/log plot (Figure 12) of coercivity ratios versus magnetization ratios which has been previously described to be indicative of primary magnetizations [Channell and McCabe, 1994]. Samples from the other areas generally plot above the primary magnetization line and below the line which has been previously interpreted to be characteristic of chemical remagnetization [e.g., Channell and McCabe, 1994].…”

Cretaceous Research: A New Constraint on the Paleostress Regime of Southwest Japan Based on Microfabric Analysis of a Granitic Pluton

“…A noteworthy fact is that the altered chip sample exhibits the so-called wasp-waisted loop shape that originates from the presence of high-coercivity components related to a remagnetization event (e.g. [16]). University.…”

“…See text for method of preparing chip and powder samples. Trends a, b and c originate from synthetic and crushed natural magnetite [15], single-domain (SD) and multidomain (MD) mixtures of magnetite [16] and superparamagnetic (SP) and SD mixtures of magnetite [17,18], respectively. Figure 8 shows examples of hysteresis loops for Toki Granite.…”

“…Among the 10 sites, magnetization of the intrusive rocks did not reach saturation at the highest field of the apparatus, so they were then excluded from the following analysis. Dynamics of Arc Migration and Amalgamation -Architectural Examples from the NW Pacific Marginmagnetite [15], single-domain (SD) and multidomain (MD) mixtures of magnetite [16] and superparamagnetic (SP) and SD mixtures of magnetite [17,18], respectively. As for the fresh granites (1), most of the data are found around mixture trends of various sizes of magnetite, implying that the effect of secondary mineral precipitation remains minimal.…”

Magnetic analysis of commercial hematite, magnetite, and their mixtures

“…The Alfa sample, however, shows a wasp-waisted loop (necking in the middle section), which can be caused by either multiple magnetic phases with varying coercivities or multiple particle size distributions. 5,14,18,19 Considering the uniform particle size distribution observed in SEM micrographs of Alfa sample, and the presence of another phase detected by XRD, the observed behavior is likely from an Fe-containing impurity phase which likely has higher magnetization and lower coercivity than hematite. The FORC diagram of the Alfa sample (Figure 2b) confirms the simultaneous presence of a multidomain (MD) lower-H C component (diverging away at the origin) and a single-domain (SD) higher-H C component (small vertical spread along the H u =0 axis).…”