Geology Commons^™

Contrasting Silicic Magma Series In Miocene-Pliocene Ash Deposits In The San Miguel De Allende Graben, Guanajuato, Mexico, Eric H. Christiansen, Bart J. Kowallis, Aaron J. Adams, Oscar Carranza-Castaneda, Wade E. Miller

Faculty Publications

The San Miguel de Allende graben, Guanajuato, Mexico, contains numerous rhyolitic volcanic ash beds. Electron microprobe and x-ray fluorescence analyses of glass shards from 14 localities, combined with mineralogic, stratigraphic, radiometric, and paleomagnetic data, allow us to correlate the ash beds (and the intervening sedimentary strata and fossils), understand the timing of volcanism, date the age of extension, and better understand the tectonic and volcanic evolution of central Mexico. Our analyses reveal that at least six separate eruptions of rhyolitic ash occurred during the Late Miocene and Pliocene (5-3 Ma) while the San Miguel Allende basin was subsiding. The fallout …