PALEOMAGNETIC DATA FROM CENTRAL MEXICO AND THEIR USE FOR PALAEOSECULAR VARIATION STUDIES

Three Brunhes-age palaeomagnetic data sets from central Mexico exhibit different dispersion of virtual geomagnetic poles. Volcanics from the eastern part of the Trans-Mexican Volcanic Belt result in a S(F) = 14.8-degrees. This value is interpreted to represent an upper limit, as these rocks probably are affected by localized tectonic rotations. For a stalagmite, S(F) = 9.5-degrees, which is interpreted as a lower limit, as the stalagmite is only 1200 years old and the data are strongly biased in time. Seventy-four volcanic units from the Chichinautzin Formation result in S(F) - 11.7-degrees, with confidence limits of 10.4-degrees and 13.3-degrees. This dispersion is much lower than expected from palaeosecular variation models, but corresponds to data obtained for other areas in or beneath the Pacific Basin, e.g. the Hawaiian islands.