TRM in low magnetic fields: a minimum field that can be recorded by large multidomain grains
| Autor: | Norman F. Ness, Peter J. Wasilewski, Mario H. Acuña, Tomas Kohout, Michael D Fuller, Emilio Herrero-Bervera, Gunther Kletetschka |
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| Rok vydání: | 2006 |
| Předmět: |
010504 meteorology & atmospheric sciences
Physics and Astronomy (miscellaneous) Thermoremanent magnetization Magnetism Demagnetizing field Mineralogy Astronomy and Astrophysics 010502 geochemistry & geophysics Condensed Matter::Disordered Systems and Neural Networks 01 natural sciences Physics::Geophysics Magnetic field chemistry.chemical_compound Geophysics Earth's magnetic field chemistry Space and Planetary Science Remanence Critical field Geology 0105 earth and related environmental sciences Magnetite |
| Zdroj: | Physics of the Earth and Planetary Interiors. 154:290-298 |
| ISSN: | 0031-9201 |
| Popis: | Thermally acquired remanent magnetization is important for the estimation of the past magnetic field present at the time of cooling. Rocks that cool slowly commonly contain magnetic grains of millimeter scale. This study investigated 1-mm-sized magnetic minerals of iron, iron–nickel, magnetite, and hematite and concluded that the thermoremanent magnetization (TRM) acquired by these grains did not accurately record the ambient magnetic fields less than 1 μT. Instead, the TRM of these grains fluctuated around a constant value. Consequently, the magnetic grain ability to record the ambient field accurately is reduced. Above the critical field, TRM acquisition is governed by an empirical law and is proportional to saturation magnetization ( M s ). The efficiency of TRM is inversely proportional to the mineral's saturation magnetization M s and is related to the number of domains in the magnetic grains. The absolute field for which we have an onset of TRM sensitivity is inversely proportional to the size of the magnetic grain. These results have implications for previous reports of random directions in meteorites during alternating field demagnetization, or thermal demagnetization of TRM. Extraterrestrial magnetic fields in our solar system are weaker than the geomagnetic field by several orders of magnitude. Extraterrestrial rocks commonly contain large iron-based magnetic minerals as a common part of their composition, and therefore ignoring this behavior of multidomain grains can result in erroneous paleofield estimates. |
| Databáze: | OpenAIRE |
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