EarthRef.org Reference Database (ERR) -- Yu et al. 2004

Paleointensity determinations based on double heating techniques (in-field/zero-field cooling, zero-field/in-field cooling, and two in-field steps with opposite laboratory fields) are generally considered to be functionally interchangeable producing equally reliable paleointensity estimates. To investigate this premise, we have developed a simple mathematical model. We find that both the zero-field first and in-field first methods have a strong angular dependence on the laboratory field (parallel, orthogonal, and anti-parallel) while the two in-field steps method is independent of the direction of the laboratory-produced field. Contrary to common practice, each method yields quite different outcomes if the condition of reciprocity of blocking and unblocking temperatures is not met, even with marginal (10%) tails of partial thermoremanence. Our calculations suggest that the zero field first method with the laboratory-produced field anti-parallel to the natural remanence (NRM) is the most robust paleointensity determination technique when the intensity of the lab-induced field is smaller than ancient field. However, the zero field first method with the laboratory-field parallel to the NRM is the optimum approach when the intensity of the lab-induced field is larger than the ancient field. By far the best approach, however, is to alternatethe infield-zerofield (IZ) steps with zerofield-infield (ZI) steps. Paleointensity determinations based on double heating techniques (in-field/zero-field cooling, zero-field/in-field cooling, and two in-field steps with opposite laboratory fields) are generally considered to be functionally interchangeable producing equally reliable paleointensity estimates. To investigate this premise, we have developed a simple mathematical model. We find that both the zero-field first and in-field first methods have a strong angular dependence on the laboratory field (parallel, orthogonal, and anti-parallel) while the two in-field steps method is independent of the direction of the laboratory-produced field. Contrary to common practice, each method yields quite different outcomes if the condition of reciprocity of blocking and unblocking temperatures is not met, even with marginal (10%) tails of partial thermoremanence. Our calculations suggest that the zero field first method with the laboratory-produced field anti-parallel to the natural remanence (NRM) is the most robust paleointensity determination technique when the intensity of the lab-induced field is smaller than ancient field. However, the zero field first method with the laboratory-field parallel to the NRM is the optimum approach when the intensity of the lab-induced field is larger than the ancient field. By far the best approach, however, is to alternatethe infield-zerofield (IZ) steps with zerofield-infield (ZI) steps.