The total amplitude of secular variations, global magnetic anomalies and plumes

The paleomagnetic directions (from Paleomagnetic Database) characterizing t he Brunhes chron and the whole Cenozoic era are used to determine the total amplitude of secular variations in the geomagnetic field (S = 81/(K)(1/2)) . The behavior of S is analyzed as a function of the distance to the neares t centers of global magnetic anomalies and deep-seated plumes. This analysi s showed that S tends to decrease with increasing distances from the center s of the global magnetic anomalies (over the last few tens of thousands of years) and from the epicenters of present plumes (50- to 30-Ma paleomagneti c records of the geomagnetic field directions). Global magnetic anomalies a lso affect paleomagnetic declinations at points located west and east of th e anomalies: average deviations from the dipole field are negative west of the anomalies and positive east of them. This effect disappears for paleoma gnetic determinations older than 100 ka. This suggests that the sources of secular variations and global magnetic anomalies are interrelated with plum es and can provide constraints on the age of the related heterogeneities in the core and on the time of the plume ascent from the core to the Earth's surface.