Magnetic Properties of Melt Particles of Suevitic Samples From the Bosumtwi Impact Structure, Ghana.

The magnetic anomaly over Bosumtwi impact structure has recently raised a debate about its origin. Plado et al. (2000) presented a magnetic model where a strongly remanently magnetized melt or melt-rich body was proposed as a source of this anomaly. Recent deep drilling through the Bosumtwi structure, however, failed to penetrate into the expected melt body. Also, the recent investigations of petrophysical parameters of samples from deep drill cores (Elbra et al., 2006) did not yield any strongly magnetic body. In order to find out whether the current drill cores simply lack the melt or the expected highly magnetized body escaped the drilling, we separated individual melt particles from deep drill core samples and from exposed suevitic rocks, and measured their magnetic properties. Preliminary results of our investigation show differences in magnetic properties between the melt from inside and outside the crater. The melt from drill core samples shows merely a paramagnetic signal of magnetic susceptibility and only a weak intensity of remanence. The melt from exposed rocks, however, shows slightly higher magnetizations. Currently, the more detailed rock-magnetic studies of separate melt inclusions, combined with X-ray diffraction measurements, are carried out in order to identify the nature of magnetic minerals in the melt and to verify if the melt is enough highly magnetic to be the source of the magnetic anomaly. References: Elbra T., Pesonen L.J. (2006) Petrophysical and rock-magnetic properties of impactites from deep drill core of Bosumtwi impact structure. Meteoritics and Planetary Science 41, Supplement, August, A49. Plado J., Pesonen L.J., Koeberl C., Elo S. (2000) The Bosumtwi meteorite impact structure, Ghana: A magnetic model. Meteoritics and Planetary Science 35, 723-732.