| Abstrakt: |
Chemical analyses have been made of non-stoichiometric (i.e. slightly oxidized) titanomagnetites in basaltic rocks from Argentina, Turkey, the Azores, the Canary Islands, Japan, Bulgaria, Aden and the Pacific area. The compositions do not differ significantly from the average compositions of titanomagnetite grains which contain ilmenite lamellae (usually taken as evidence of deuteric oxidation) in other basalts from the same regions and also from Oregon. The shapes of the thermomagnetic curves are considered to provide a rapid and useful approximation to the degree of non-stoichiometry. This has been determined more precisely from observations that the measured Curie points are invariably higher than the compositional ones, calculated for stoichiometric titanomagnetites of the same composition. The degree of non-stoichiometry so obtained has been represented by plotting the estimated compositions of the grains studied on a triangular plot. |
Plný text