Adrian Muxworthy: A practical Preisach approach for correcting palaeointensities for cooling rate
Channel: Institute for Rock Magnetism
Date: 02/06/2021

12th Institute for Rock Magnetism Conference 

Lightning Talk

Title: A practical Preisach approach for correcting absolute palaeointensities for cooling rate

Authors: Adrian Muxworthy & Evelyn Baker

Title: Department of Earth Science and Engineering, Imperial College London, London, UK 

Abstract:
It is long established that thermoremanent magnetization (TRM) intensity depends on cooling rate. This is a problem as most standard methods of determining absolute paleointensities replace natural TRM acquired in nature, with TRM acquired in the laboratory in a known applied field. In most circumstances the cooling time of the natural TRM is significantly longer than those acquired in the laboratory, i.e., times of approximately one month for basalts for basalts, but potentially greater than 100 kyrs for intrusive rocks, versus one hour respectively. This difference is thought to cause a significant difference in the final intensity estimate of ~5–10%. If a sample suite is known to come from a rock with a long cooling time, then typically a blanket correction is applied to all the samples.

We have developed a practical approach for correcting palaeointensities for cooling rate using Preisach theory. This method uses the FORC diagram measured for a sample to generate a unique cooling correction for each temperature in a Thellier-type measurement, after which the palaeointensity is estimated, i.e., the palaeointensity is determined for a cooling-rate corrected Arai plot data. This is a more sophisticated approach than the standard blanket approach, providing a unique correction for every sample at every temperature. We plan to submit this for publication, after which we make this tool available as a Jupyter notebook.