The memory of fire in El Coporo (Northern Mesoamerica): Apogee and abandonment

Abstract Most detailed archaeometric studies come from central and southern Mesoamerica while many important sites belonging to the western regions are not yet rigorously studied. Here we report a detailed rock-magnetic and archaeomagnetic study from the El Coporo archaeological site at the northern border of Mesoamerica. Our study of more than 100 oriented samples was performed on the six most important sites distributed along the archaeological zone. Continuous thermomagnetic curves revealed magnetite as responsible for magnetization accompanied by unstable (titano)maghemite. Most of the samples are characterized by a single component magnetization, which is almost completely removed applying 50 mT, suggesting the presence of relatively low coercivity magnetic minerals. Characteristic directions were precisely determined for four out of six studied sites, yielding statistically undistinguishable directions. Corresponding archaeomagnetic age intervals range from 820 to 950 A.D. in good agreement with previous archaeological studies that suggested a period of abandonment at about 900 A.D. as an attempt to reoccupy the place by the Toltecs. Numerous archaeological evidences argue in favor of an intentional fire. However, the possibility of ritual closure should be also considered since there is no evidence of violent or warlike actions.