Late Quaternary volcanic record from lakes of Michoacán, central Mexico

This paper describes the initial stages of the development of a tephrochronology for the region of the Michoacán–Guanajuato volcanic field (MGVF) in central Mexico. There are two elements to this: the geochemical characterisation of volcanic glass and the linkage of tephra deposits to eruptions of known age. The MGVF is dominated by cinder cones and shield volcanoes which erupt only once. There are only two stratovolcanoes (multiple eruptions) which are common elsewhere in the Trans-Mexican Volcanic Belt. Tephras were sampled from sub-aerial sites close to cones of known age and from lake sediment cores from the Zirahuén, Pátzcuaro and Zacapu basins in the State of Michoacán. Multiple samples were collected to ensure that each tephra was well represented. The glass was analysed by electron microprobe and found to be calc-alkaline in composition. SiO2 abundances varied from 52% to 75%. Full results are available at http://www.geo.ed.ac.uk/tephra/. The ages of the dated cones ranged from the 20th century AD to ca 17,000 14C years BP. Tephras from eruptions of El Jabali (3840 14C years BP), Jorullo (1759–1774) and Paricutín (1943–1952) have been identified in lake cores. These provide a means of correlating between basins and have the potential to provide a basis for understanding the volcanic history of this area and for dating a wider range of sediment sequences