Thermomagnetic curves of selected phonolites and trachytes of the České středohoří Mts.

 

Štěpánka Mrázová, Marta Chlupáčová, Vladimír Cajz

Geoscience Research Reports 46, 2013 (GRR for 2012), pages 316–319

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Abstract

Variability of the temperature dependence of magnetic susceptibility and crystalochemical properties of the Fe-Ti oxides have been investigated in 21 selected young felzic alkaline volcanic rocks of the České středohoří Mountains. It was confirmed that magnetization of the rocks is mainly caused by ferromagnetic minerals depending not only on the mineral type and grain size, but also on the contents of Fe-substituting elements in it. Curie temperature (TC) of the rocks containing titanomagnetite (Fe2+1+xFe3+2.2xTix04) depends mainly on the value of x (titanomagnetite content) and, in addition, on the contents of the Tc-lowering impurities such as AI, Mg, Mn, and Cr. For felzic volcanic rocks with titanomagnetites the heating thermomagnetic curves show very similar shape, with TC between 420-550 °C. The heating curves of the samples without Fe-Ti oxides but with silicates, for examples egirine, have a hyperbolic shape and correspond to paramagnetic minerals.