<P> In geophysics , a magnetic anomaly is a local variation in the Earth 's magnetic field resulting from variations in the chemistry or magnetism of the rocks . Mapping of variation over an area is valuable in detecting structures obscured by overlying material . The magnetic variation in successive bands of ocean floor parallel with mid-ocean ridges is important evidence supporting the theory of seafloor spreading , central to plate tectonics . </P>
<P> In geophysics , a magnetic anomaly is a local variation in the Earth 's magnetic field resulting from variations in the chemistry or magnetism of the rocks . Mapping of variation over an area is valuable in detecting structures obscured by overlying material . The magnetic variation in successive bands of ocean floor parallel with mid-ocean ridges is important evidence supporting the theory of seafloor spreading , central to plate tectonics . </P>
magnetic reversals ( i.e. the cause of marine magnetic anomalies ) are caused by
magnetic reversals ( i.e. the cause of marine magnetic anomalies ) are caused by
variations in the chemistry or magnetism of the rocks
variations in the chemistry or magnetism of the rocks