Changes

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[[file:using-magnetics-in-petroleum-exploration_fig14-5.png|300px|thumb|{{figure number|1}}]]

[[file:using-magnetics-in-petroleum-exploration_fig14-5.png|300px|thumb|{{figure number|1}}Geologic map of an area of crystalline basement in central Wisconsin on the southern edge of the Canadian Shield. From LaBerge, 1976; courtesy International Basement Tectonics Assoc.]]

A major pitfall in interpreting magnetic residual maps is assuming that magnetic highs and lows are caused by elevation changes on basement rocks in a sedimentary basin. To the contrary, most magnetic anomalies are caused by lithologic changes and the corresponding changes in susceptibility. As shown in [[:file:using-magnetics-in-petroleum-exploration_fig14-5.png|Figure 1]], the basement is of complex lithology and is highly fractured. The fractures divide the basement into blocks and are zones of weakness along which faults occur. The most important and most reliable information obtainable from aeromagnetic maps is the configuration (in plan view) of the underlying basement fault block pattern.

A major pitfall in interpreting magnetic residual maps is assuming that magnetic highs and lows are caused by elevation changes on basement rocks in a sedimentary basin. To the contrary, most magnetic anomalies are caused by lithologic changes and the corresponding changes in susceptibility. As shown in [[:file:using-magnetics-in-petroleum-exploration_fig14-5.png|Figure 1]], the basement is of complex lithology and is highly fractured. The fractures divide the basement into blocks and are zones of weakness along which faults occur. The most important and most reliable information obtainable from aeromagnetic maps is the configuration (in plan view) of the underlying basement fault block pattern.