Cation diffusion in titanomagnetites

Alteration of titanomagnetites and its related magnetic properties in the Noya geothermal area, central Kyushu, Japan.

“…They concluded that low temperature oxidation involved diffusion of Fe out of the original spinel lattice into surrounding silicates, which would result in an increase of the Ti/ Fe ratio for the remaining Fe-Ti oxide. ARAGON et al (1984) clarified the slow diffusion rate of Ti compared to that of Fein Our observations and analytical results are consistent with their conclusion. The characteristic features of subaereal low temperture oxidation are similar to those of submarine low temperature oxidation.…”

“…Ca and Si must be introduced by hydrothermal fluid from surrounding silicates for sphene mineralization. Considering the lower diffusivity of Ti compared to Fe in titanomagnetites (ARAGON et al, 1984), this exchange cannot be explained by only lattice diffusion, and cations migration by hydrothermal fluid probably plays an important role. The rapid reaction rate of oxide minerals compared to that of silicates gives rise to recrystallization of pure magnetite after titanomagnetites, even though the other silicate minerals suffer only slight hydrothermal alteration.…”

Impact of irradiation‐induced point defects on electronically and ionically induced magnetic relaxation mechanisms in titano‐magnetites

“…Moreover, Frenkel defects of higher formation enthalpies may, generally, be assumed to form closer pairs, undergoing faster recombination on thermal annealing, than larger--distance pairs associated with lower formation enthalpies. This rule may be relativized, however, with respect to Ti 4+ -type Frenkel pairs in view of the considerably higher migration enthalpy of Ti 4+ [21,22], as compared to Fe 2+ [22,23] and O 2interstitials [24].…”

A cascade of magmatic events during the assembly and eruption of a super-sized magma body

“…14 and S.9). Fe-Ti oxides, and magnetite in particular, are known to rapidly re-equilibrate in response to fluctuations in magmatic conditions (Freer and Hauptman 1978;Aragon et al 1984;Nakamura 1995;Venezky and Rutherford 1999;Coombs et al 2000;Devine et al 2003).…”