Magnetic Anomalies of Impact Craters at Low Magnetic Latitudes

Abstract

Hypervelocity meteor impacts create circular or ova l craters and fracture the subsurface. This fracturing has been associated with geothermal reso urces, metallic ore deposits, and even oil and gas fields. These practical targets give the study of meteor impacts importance aside from the several more basic scientific reasons for impact crater research . An examination of the worldwide distribution of known impact crater locations shows that very few c raters appear on or near the magnetic equator. Although this could be mere chance, it is possible that some low latitude impact craters are buried or hidden by heavy vegetation and are overlooked because their magnetic anomalies do not appear particularly ring-like. Magnetic anomalies from im pacts are variable, but three main categories captu re the majority: (1) simple ring anomalies created by the uplifted rim of the crater, (2) complex crater anomalies consisting of an outer ring and a center anomaly, and (3) a simple crater filled with nonmagnetic debris in modestly magnetic bedrock. At l ow magnetic latitudes, each of these types can produce induced magnetic anomalies with sufficient magnitudes for detection by aeromagnetic surveys, but which are not decidedly ring-like in appearance . Low latitude rings usually show sizeable anomali es only at their north, south, east, and west extremit ies. The east and west anomalies may not be large enough spatially to detect with wide line spacing, but the north and south anomalies are usually spati ally broad. Most of the remainder of the ring is of suc h low magnitude as to be almost undetectable. Complex craters produce sizeable magnetic lows in t he center. Craters filled with non-magnetic debris may produce detectable magnetic highs. The ability to predict what types of anomalies may be formed by low magnetic latitude impact craters may be usef ul in identifying these structures in areas such as West Africa or Brazil, where dense vegetation and p oor access make detailed initial inspection problematic.