New criteria for selecting reliable Thellier-type paleointensity results from the 1960 Kilauea lava flows, Hawaii

Thellier-type paleointensity experiments associated with partial thermal remanent magnetization checks have been widely used to determine paleointensity values from volcanic and archaeological media. However, previous studies have revealed that a substantial portion of paleointensity results with positive checks for historical lava samples largely fails to predict known Earth magnetic field intensity values. To determine the fidelity of paleointensity values, conventional Thellier-type paleointensity experiments were performed on Kilauea lava flows that erupted in 1960. The positive partial thermal remanent magnetization checks for our results range from 30.28 ± 1.38 µT to 52.94 ± 1.89 µT. This strongly indicates that conventional paleointensity checks cannot guarantee the fidelity of paleointensity results, especially when the unblocking temperatures for the newly formed magnetic particles are higher than the treatment temperature. Therefore, in this study, to check for thermal alteration during heating, the temperature dependence of the hysteresis parameter measured at room temperature for the thermally treated samples was also measured. Our new results show that nearly all biased paleointensity values correspond to a ratio of the coercivity of remanence to the magnetic coercivity of > 3 and a chemical alteration index > ~ 10%, which indicates the strong effect of the domain state and thermal alteration on the fidelity of the paleointensity results. Our study provides feasible criteria to further improve the fidelity of paleointensity estimations.

New Criteria for Selecting Reliable Thellier-Thellier type Paleointensity Results from the 1960 Kilauea Lava Flow, Hawaii

Thellier-Thellier type paleointensity experiments associated with partial thermal remanent magnetization (pTRM) checks have been widely used to determine paleointensity values from volcanic and archaeological media. However, previous studies further revealed that a substantial portion of paleointensity results with positive checks for historical lavas largely fails to predict the known Earth’s field intensity values. To determine the fidelity of paleointesnity values, conventional Thellier-Thellier type paleointensity experiments have been performed from the Kilauea lava flows erupted in 1960. Our results show that positive pTRM checks range from 30.34±1.39 to 53.04±1.80 μT. This strongly indicates that positive pTRM checks can’t guarantee the fidelity of paleointensity results especially when the unblocking temperatures for the newly-formed magnetic particles are higher than the treated temperature. Thus, in this study, to check thermal alteration during heating, the temperature-dependent of hysteresis parameter measured at the room-temperature for the thermally-treated samples were also measured. Our new results show that almost all biased paleointensity values correspond to Bcr /Bc >3 and CI >~10%, which indicates strong effects of domain state and thermal alteration on the fidelity of paleointensity results. Our study provides a feasible criteria to further improve the fidelity of paleointensity estimations.

Photo-induced magnetic behavior in the amorphous spin-glass material Co3(SbTe3)2

A new ternary material Co3(SbTe3)2 was prepared by using a rapid precipitation metathesis reaction between the Zintl material K3SbTe3 and CoCl2 in aqueous solution. The dc specific resistivity of this material is in the region for metallic conductors (p = 2.75 × 10-3 Ω-cm). The dc magnetic susceptibility of Co3(SbTe3)2 is reported over a 2.2 K-300 K temperature region, and the material is characterized as a spin glass with a freezing temperature of about 5 K. Magnetization data are also reported as both thermal remanent magnetization and isothermal remanent magnetization as a function of magnetizing field and temperature. When cooled well below the glass freezing temperature, the frozen spin glass has been observed to exhibit photomagnetic effects consistent with a disruption of the spin-glass state caused by uv-radiation.

Infidélité paléomagnétique observée dans une formation lacustre varvée quaternaire dite: "argiles d'Eybens" (Grenoble, France)

We have investigated the properties of natural magnetization of a lacustrine interglacial Riss–Würm deposit near Grenoble (France). Made up of accumulated argillite 250 m thick, this deposit comprises annual varves with an average thickness of 0.5 cm.The magnetic viscosity of this sediment is not very high, and we have demonstrated that the characteristic magnetization, measured after a moderate thermal treatment (between 160 and 220 °C) followed by alternating field demagnetization with maximum intensity at 200 Oe (15.9 × 103 A/m), is possibly a detrital magnetization carried by the magnetite (thermomagnetic and strong continuous field studies).On a local scale (area of about 100 m2), the direction of this magnetization remains very homogeneous within each horizon; sampling restricted to about 10 sites 1 m apart indicates for each level a mean direction of magnetization with a high accuracy: α95 = 1–2°, k = 500–2500. The aveage direction calculated by this method for different levels indicates significant stratigraphic variations (attaining an inclination of 20° and a declination of 50°), which are reached rapidly (from 1 to few degrees per year). Such variations cannot be reasonably attributed to changes in the directions of the Earth's magnetic field.A study of the acquired anisotropy of the thermal remanent magnetization indicates a magnetic anisotropy that is related to the lithological structure of the sediment and shows a strong intensity: the maximum divergence between the field direction and the acquired thermal remanent magnetization direction in this field varies, with individual samples, between 9 and 50°. The study of the properties of this anistotropy demonstrates the "infidelity" of the detrital magnetization: for one of the small vertical sequences studied for anisotropy the characteristic magnetization of a specified level has a direction nearer the axial direction of easy magnetization when the anisotropic intensity is large. This infidelity may be caused by different factors influencing the deposition of the sediment, particularly the variable directions of water flows determining the particle orientation. [Journal Translation]