MAGNETIC ANOMALY NEAR THE CENTER OF THE VREDFORT STRUCTURE - IMPLICATIONS FOR IMPACT-RELATED MAGNETIC SIGNATURES

A strong magnetic anomaly near the center of the ancient and deeply er oded Vredefort structure is attributed to remanent magnetization cause d by a large meteorite impact at similar to 2.0 Ga. The rocks underlyi ng the anomaly are Archean gneisses thought to represent mid-crustal d epths that were uplifted to the surface during the postulated impact e vent. Measurements of the remanent magnetization of the basement rocks yielded consistent vectors of declination = 25 degrees, inclination = 56 degrees, k = 18, alpha = 16 that correspond to the paleomagnetic p ole position at time of impact. Petrologic studies indicate that durin g impact, large volumes of rock were heated enough to cause thermal re magnetization in the ambient field. Thermal effects of all large impac ts on cratons may induce a remanent magnetization of sufficient intens ity to cause anomalies in the geomagnetic field that are detectable ev en by satellites.