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 of a different magnetic field. The temperature ranges
over which these remanence components demagnetize can overlap, making it
difficult to determine their directions. We present a data analysis tool
called Thermal Resolution Of Unblocking Temperatures (TROUT) that treats
the process of thermal demagnetization as a function of temperature (or
alternating field demagnetization as a function of coercivity). TROUT
models the unblocking temperature distributions of components in a
demagnetization experiment, allowing these distributions to overlap.
TROUT can be used to find the temperatures over which paleomagnetic
directions change and when two directional components overlap resulting
in curved demagnetization trajectories. 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 to within 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 history of a specimen is of interest (e.g. emplacement
temperature of pyroclastic deposits, re-heating of archaeological
artifacts, reconstruction of cooling rates of igneous bodies). The
ability to determine whether a single component or multiple components
are demagnetizing at a given temperature is useful for choosing
appropriate ranges of temperatures to use in paleointensity experiments.
Finally, the width of the range of temperature overlap may be useful for
inferring the domain state of magnetic mineral assemblages.