versão impressa ISSN 0016-7169
LAYER, P. W. et al. El Chichón volcanic complex, Chiapas, México: Stages of evolution based on field mapping and 40Ar/39Ar geochronology. Geofís. Intl [online]. 2009, vol.48, n.1, pp. 33-54. ISSN 0016-7169.
A new interpretation of the evolution of El Chichón volcano is presented in this paper based on photogeology, fieldwork, 40Ar/39Ar dating and chemistry of juvenile products. El Chichón volcano belongs to a volcanic complex formed by craters and peripheral domes with a total estimated volume of ~26 km3. Our data suggest that inception of magmatism began around 370 ka with the emission of lava domes buried by younger products. The activity continued with the formation of a large andesitic dome complex between 209 and 276 and associated block and ash flows and lahars. The dome complex was subsequently destroyed by a major eruption that left a 1.5-km wide Somma-type crater. The activity continued with the extrusion of the SW dome at 217 ka, that partially disrupted the southwestern Somma crater wall. Later on a series of dome extrusions occurred beyond the northwestern sector of the Somma crater at about 95 ka. Juvenile blocks found in 1982 products yielded ages of 44 and 29 ka attesting to heretofore unidentified late Pleistocene activity. The onset of Holocene activity occurred both outside the Somma crater with explosive eruptions that formed the Guayabal Tuff Cone and inside the Somma crater with the formation of a tuff cone that has been repeatedly reactivated during the Holocene, lastly during the 1982 eruption. All magmas produced during the past 370,000 years are K-alkaline andesites that exhibit minor variation in their chemical composition. An average discharge rate of 0.5 km3/ka is calculated during the past 8,000 years (~4 km3).
Palavras-chave : 40Ar/39Ar dating; evolution; volcanic complex; Chichón; México.