ThellierCoolPy: A Cooling-Rate Correction Tool for Paleointensity Data

We report a new approach of implementing cooling-rate corrections in absolute ancient magnetic field intensity (paleointensity) studies. Nearly all methods of determining paleointensity estimates rely on rocks having recorded a thermoremanent magnetization (TRM), on cooling from above the rock's constituent minerals' Curie temperature. Typically paleointensity estimates are made by comparing natural TRM, with a TRM induced in the laboratory; however, TRM intensity has long been reported to be dependent on cooling rate. Natural cooling rates are impractical in laboratories. We have developed a new cooling-rate correction method and corresponding software (ThellierCoolPy), that directly corrects the unprocessed paleointensity data, using first-order reversal curve data collected on a sister sample. This site tailored cooling-rate correction has a unique correction for each temperature step within the paleointensity data set. This new method differs from previous approaches which apply a blanket cooling-rate correction independent of the material properties of the sample. Paleointensity data from historical lavas from Paricutin, Mexico, are used to demonstrate the new software. For this data set, it is shown that cooling time of 1 million years yields a reduction of the paleointensity of similar to 7%. The software is available for download.