LAUSR

Abstract Our knowledge of the Earth's magnetic field intensity changes over the past few thousand years is still limited because of the uneven spatial and temporal distribution of data, which also includes the Americas. The present study reports 41 new palaeointensity data covering the past 3600 years which, together with 38 previously published data of similar quality, are used to construct a palaeointensity secular variation curve for Central Mexico. These new data are an important contribution to the global intensity database and will also improve the application of palaeomagnetic dating in Mexico, which is of interest because of the many Holocene monogenetic volcanoes within the Trans-Mexican Volcanic Belt, and of its archaeological heritage. The most conspicuous feature of the new intensity curve is the rapid increase between 400 and 250 BCE, from about 45 to 65 μT. Other relative intensity highs of ≈45–55 μT were found around 1600 BCE, 370 CE, and 1200 CE and relative intensity lows of ≈30–35 μT around 1350 BCE and 700 CE. Comparing the virtual axial dipole moment of our intensity curve with global VADM-VDM dipole estimates indicates that non-dipole components in Central Mexico have been observed at several times from 1600 BCE to 1000 CE while the dipole field was prevalent from 1000 to 1800 CE. A comparison of our results with selected data from southern USA shows a significant difference between the two regions which indicates an important nondipole feature of the magnetic field during the last few thousands of years, and/or undetected problems in the age/palaeointensity data accuracy.