Nature of magnetic grains and their effect on the remanent magnetization of basalts |
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| Authors: | C Radhakrishnamurty SD Likhite PW Sahasrabudhe |
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| Institution: | 1. Tata Institute of Fundamental Research, Bombay 5, India;2. Physics Department, Fourah Bay College, Freetown, Sierra Leone |
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| Abstract: | The nature of magnetic grains in basalts obtained from different parts of the world has been investigated. Results indicate that magnetic behaviour attributable to cation-deficient magnetite is common in basalts younger than Cretaceous, while that due to multidomain magnetite is widespread in much older rocks. Superparamagnetic grains occur in basalts more abundantly than originally presumed, which seem to be mainly responsible for the viscous remanent magnetization of such samples. Basalts which are inferred to contain predominantly optimum single-domain grains are found to be most suitable for palaeomagnetic work. However, many samples generally contain a wide range of grain sizes and this can account for the observed variation in their magnetic stability. One possible mechanism for the formation of such magnetic grains in basalts and its implications to palaeomagnetism is presented. Basalts whose magnetic behaviour is completely reversible on heating and cooling are very rare and because of this fact the reliability of palaeointensity determinations, involving heating of the samples even for one time, may be reduced to a considerable extent. |
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