Thermal Resolution of Unblocking Temperatures (TROUT): A Method for "Unmixing" Multi-Component Magnetizations

Abstract

Some rocks contain multiple remanence “components,” each of which preserves a record ofa different magnetic field. The temperature ranges over which these remanence components unblock canoverlap, making it difficult to determine their directions. We present a data analysis tool called ThermalResolution Of Unblocking Temperatures (TROUT) that treats the process of thermal demagnetization as afunction of temperature (or alternating field demagnetization as a function of coercivity). TROUT models theunblocking temperature/coercivity distributions of components in a demagnetization experiment, allowing thesedistributions to overlap. TROUT can be used to find the temperatures/coercivities over which paleomagneticdirections change and when two directional components overlap resulting in curved demagnetizationtrajectories. When applied to specimens given multi-component Thermoremanent Magnetizations (TRMs)in the laboratory, the TROUT method estimates the temperature at which the partial TRMs were acquired towithin one temperature step, even for specimens with significant overlap. TROUT has numerous applications:knowing the temperature at which the direction changes is useful for experiments in which the thermal historyof a specimen is of interest (e.g., emplacement temperature of pyroclastic deposits, re-heating of archaeologicalartifacts, reconstruction of cooling rates of igneous bodies). The ability to determine whether a singlecomponent or multiple components are demagnetizing at a given temperature is useful for choosing appropriateranges of temperatures to use in paleodirection/intensity experiments. Finally, the width of the range oftemperature overlap may be useful for inferring the composition, grain size and domain state of magneticmineral assemblages.