On correction of loss of mass during Thellier experiments

Determination of geomagnetic paleointensity by the Thellier method compares the decay of natural remanent magnetisation with the gain of a laboratory induced thermoremanent magnetisation. If fragile samples lose some amount of their material after each heating step, the Thellier experiment will be systematically disturbed and paleointensity will be over-estimated. For a lost of 5% of the sample’s mass an over-estimate of 10% in paleointensity is observed. This can easily be corrected by a normalisation to the initial mass of the unheated sample. This is necessary for any fragile materials such as baked clays or when a specimen breaks into pieces during the Thellier experiment.