First Full Vector Archeomagnetic Data From Northern Mexico

Several regional secular variation curves of the geomagnetic field have been proposed for Mexico over the last millennia. Despite a fairly large number of archeomagnetic data, these curves remain imprecise because of an uneven quality and geographic distribution, with a lack of data in Northern Mexico. Nine pottery kilns were sampled in Casas de Fuego, an archeological site in the Chihuahua state. These kilns belong to the Casas Grandes culture and were in use between 1250 and 1450 CE. Rock magnetic experiments indicate that the main magnetic phase is a Ti-poor titanomagnetite in the SD range. Mean characteristic directions per kiln were estimated by alternating field and/or thermal demagnetization, and archeointensities with the Thellier-Thellier protocol, after correction for anisotropy and cooling effects. The nine directions and eight intensities agree with data from USA and Mexico but do not support the peak in inclination modeled by the Mexican secular variation curve around 1200-1300 CE. For the last millennium, the Western North American curve is consistent with the SHAWQ2k global model, and better reflects the secular variation in Northern Mexico. For intensity, neither the SHAWQ2k model nor the regional intensity curve can depict the rapid secular variation that likely occurs circa 1500 CE. The Casas de Fuego results are the first full vector determinations obtained in Northern Mexico.