Magnetic properties of Kurokami pumices from Mt. Sakurajima, Japan

Both chromite and low-Ti titanomagnetite are carriers of natural remanent m agnetization (NRM) in Kurokami andesitic pumices of Mt. Sakurajima, Japan. Thermal demagnetization of the NRM and of a laboratory isothermal remanence indicate unblocking of chromite remanence between 200 and 260 degreesC and of titanomagnetite remanence between 400 and 510 degreesC. Electron microp robe analyses support the compositions Fe(1.9)Cr(1.1)1O(4) and Fe2.9Ti0.1O4 indicated by the respective Curie temperatures of 260 degreesC and 520-530 degreesC. Chromite is thermally unstable and converts to magnetite during thermal demagnetization, leading to a self-reversal of NRM between 500 and 580 degreesC. The chromite contributes about 25% of the NRM intensity of th e sample. (C) 2001 Elsevier Science B.V. All rights reserved.