Effect of gyroremenance on relative paleointensity estimates applied to ignimbrite

Abstract

Abstract Anhysteretic remanent magnetization (ARM) data serve many applications in the geosciences, such as quantifying the paleomagnetic field intensity, the magnetic grain size distributions in rocks, the degree of particle alignment from flow processes, and the emplacement and strain histories of rocks. However, the use of an alternating field when imparting or removing an ARM may give rise to a gyroremanent magnetization (GRM), which is a spurious signal that can bias ARM data. In this paper, we demonstrate the effect of GRM on ARM acquisition and demagnetization through an example of a relative paleointensity measurement. We describe a method using singular spectrum analysis to remove GRM acquired during static alternating field demagnetization (GRMAF). Another GRM component (GRMARM) is acquired during ARM acquisition. GRMARM is progressively removed during AF demagnetization, which results in a demagnetization spectrum containing two overlapping components (ARM and GRMARM). A second progressive demagnetization of a GRM imparted on the sample using an AF protocol with the same peak field as that used to impart the ARM, should contain the identical GRMARM component as acquired during the original ARM demagnetization. When separately measured, GRMARM can be subtracted from the original ARM demagnetization as a means of isolating a GRM-free ARM. Although we restrict our discussion to relative paleointensity, the methods described herein are applicable to any study involving alternating fields in paleomagnetic laboratory experiments.