CERRO-XALAPAXCO - AN UNUSUAL TUFF CONE WITH MULTIPLE EXPLOSION CRATERS, IN CENTRAL MEXICO (PUEBLA)

Authors
Citation
Mj. Abrams et C. Siebe, CERRO-XALAPAXCO - AN UNUSUAL TUFF CONE WITH MULTIPLE EXPLOSION CRATERS, IN CENTRAL MEXICO (PUEBLA), Journal of volcanology and geothermal research, 63(3-4), 1994, pp. 183-199
Citations number
36
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Geology
ISSN journal
0377-0273
Volume
63
Issue
3-4
Year of publication
1994
Pages
183 - 199
Database
ISI
SICI code
0377-0273(1994)63:3-4<183:C-AUTC>2.0.ZU;2-M
Abstract
The Xalapaxco tuff cone is located on the northeast flank of La Malinc he stratovolcano in central Mexico. An unusually large number (10) of explosion craters, concentrated on the central and on the uphill side of the cone, expose alternating beds of stratified surge deposits and massive fall deposits. The morphology of the cone and the characterist ics of its deposits point to the involvement of significant quantities of groundwater during its eruption. The phreatomagmatic eruptions whi ch led to the cone's formation pierced an alluvial fan, whose source i s a glacially carved canyon near the summit of La Malinche volcano. Th e large canyon was cut during repeated glacial episodes, the last of w hich ended ca. 8500 years ago. The present alluvial fan mostly consist s of reworked glacio-fluviatile andesite/dacite material from La Malin che. Rising magma encountered substantial amounts of groundwater withi n the limestone basement and in overlying intercalated pyroclastic and glacio-fluviatile deposits of the alluvial fan. Short-lived phreatoma gmatic eruptions produced surge and airfall deposits. Xenoliths found in the cone beds are composed of dacite and andesite clasts, limestone , chert, and rare ignimbrite fragments. No juvenile material could be unequivocally identified, but is represented most probably by porphyri tic dacite similar in texture and composition to La Malinche lavas. Th e multiple craters were formed as a response to changes in water and m agma supply during the short-lived eruption. Hence, the locations wher e ideal magma/water ratios existed to fuel phreatomagmatic explosions shifted in time and space. Analysis of diameter/depth ratios of the cr aters indicates that the activity shifted from the center of the cone to its periphery in the west. Due to the configuration of the hydrogra phic environment, more groundwater flowing from La Malinche was availa ble from the fan on the uphill side than below the cone at later stage s of the eruption. The apparently anomalous position of the tuff cone on the slopes of a stratovolcano in a presently dry environment can be explained by more humid climatic conditions prevailing at the time of eruption.