A new Approach for Absolute Paleointensity Determination: Consideration on Blocking Processes Between Temperature and Interaction-Field

Numerous paleomagnetic studies showed that only rarely the magnetic carriers in rocks are pure non- interacting single-domain (SD) grains. In most cases, samples contain mixture of pseudo-single domain (PSD), multidomain (MD), and/or SD particles with strong magnetic grain/or domain interactions. Our recent investigations indicate that magnetostatic interactions within magnetic particles can seriously affect the properties of thermal remanent magnetization (TRM) and generate non-ideal behavior for the Thellier-Coe paleointensity experiment. Here we present a new method for absolute paleointensity determination for the case where magnetostatic interactions among particles generally exist. We demonstrate that, with the presence of strong magnetostatic interactions, grain's unblocking temperature (Tub) will not equal to its blocking temperature (Tb). Significant viscous effect will also exist, that is, TRM will be blocked or unblocked more at slower cooling or heating rate. At the temperature that is higher than the ideal maximum Tub of an assemblage of clustered SD particles, the interacting field will disappear statistically, the particles will be reset, and acquire a completely magnetized TRM (CM_TRM) during successively cooling, which is identical to the total TRM (cooled from Curie temperature to room temperature). This is the crucial point of our new experimental method for paleointensity determination: we compare the unblocking temperature spectra of the CM_TRM part of an artificial TRM with that of natural remanent magnetization (NRM) to estimate paleointensity, rather than comparing the unblocking spectra of NRM with blocking spectra of progressive artificial TRM, which is used in the traditional Thellier-Coe method. The premise of our new method is that, if the unblocking spectra of CM_TRM of an artificial TRM can be obtained before significant laboratory physicochemical alteration occurs, a reliable paleointensity can be extracted from samples, even for those samples that contain PSD and MD grains. To illustrate these characteristics and validate our method, we have conducted detailed experiments on several representative artificial magnetite samples and will present these results at the meeting.