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Riisager, P. and Riisager, J. (2001). Detecting multidomain magnetic grains in Thellier palaeointensity experiments. Physics of the Earth and Planetary Interiors 125(1-4): 111-117. |
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The Thellier technique is the most commonly used method for absolute palaeointensity studies. It is based on Thellier's laws stating that partial thermoremanent magnetisations (pTRMs) are independent and additive, which however only are true for non-interacting single domain (SD) grains. For multidomain (MD) grains, individual pTRMs are not independent and Thellier palaeointensity experiments on rocks with a significant proportion of MD grains may therefore lead to erroneous palaeofield estimates. By introducing a 'pTRM-tail check' in the Coe version of the Thellier technique [J. Geophys. Res. 72 (1967) 3247], we present a simple method to detect and discard such rocks. The usefulness of the pTRM-tail check is exemplified by Thellier palaeointensity experiments performed on two palaeomagnetic sample collections with different magnetomineralogy. Miocene baked sediments from French Massif Central are shown to be ideal for Thellier studies with the remanent magnetisation residing in thermally stable SD grains. For Palaeocene-Eocene basaltic lavas from Faeroe Islands, 64% of otherwise acceptable palaeointensity estimates are discarded due to the failure of pTRM-tail checks indicating the presence of significant concentrations of MD grains. |
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Keywords
Atlantic Ocean Islands, basalts, Cenozoic, Central Massif, detection, Europe, experimental studies, Faeroe Islands, France, igneous rocks, laboratory studies, lava, magnetic domains, magnetic intensity, magnetization, multidomains, paleomagnetism, remanent magnetization, sedimentary rocks, Tertiary, Thellier Method, thermoremanent, magnetization, volcanic rocks, Western Europe, 18, Solid-earth geophysics |
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Publisher
Elsevier Science
P.O. Box 211
1000 AE Amsterdam
The Netherlands
(+31) 20 485 3757
(+31) 20 485 3432
nlinfo-f@elsevier.com |
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