HR: 14:30h
AN: U53A-03    [Abstracts]
TI: Ignimbrite Flare-up in the North-Central Sierra Madre del Sur, Southern Mexico: a Continuation of the Sierra Madre Occidental Ignimbrite Province?
AU: * Moran-Zenteno, D J
EM: dantez@servidor.unam.mx
AF: Instituto de Geologia UNAM, Ciudad Universitaria Delegacion Coyoacan, Mexico, D.F 04510, Mexico
AU: Alba-Aldave, L
EM: aldave@servidor.unam.mx
AF: Instituto de Geologia UNAM, Ciudad Universitaria Delegacion Coyoacan, Mexico, D.F 04510, Mexico
AU: Gonzalez-Torres, E A
EM: eagtgaia@geologia.unam.mx
AF: Instituto de Geologia UNAM, Ciudad Universitaria Delegacion Coyoacan, Mexico, D.F 04510, Mexico
AU: Martiny, B
EM: martiny@servidor.unam.mx
AF: Instituto de Geologia UNAM, Ciudad Universitaria Delegacion Coyoacan, Mexico, D.F 04510, Mexico
AU: Bravo-Diaz, B A
EM: dbbeatriz@yahoo.com.mx
AF: Instituto de Geologia UNAM, Ciudad Universitaria Delegacion Coyoacan, Mexico, D.F 04510, Mexico
AU: Sohn, E
EM: sohn@astroscu.unam.mx
AF: Instituto de Geologia UNAM, Ciudad Universitaria Delegacion Coyoacan, Mexico, D.F 04510, Mexico
AB: The north-central Sierra Madre del Sur, immediately south of the Trans Mexican Volcanic Belt, is made up of a series of Eocene silicic volcanic centers distributed along a WNW trending 300 km long belt from Valle de Bravo to Huautla (98°50'-100°30'W longitude). This belt constitutes an inland arc near parallel to, and coeval with, the coastal batholitic belt of southern Mexico. It includes at least 9 exhumed volcanic edifices that display diverse caldera styles controlled by regional fracture zones and rheological contrasts in the host rocks. Initiation of the volcanism ranges from 37 Ma in the west to 32 Ma in the east, and extinction of magmatism was nearly simultaneous in the eastern half of the belt. Southwest of the silicic volcanic belt, andesitic volcanism is slightly younger (33-29 Ma) and the combined effect of post-Eocene uplift and erosion removed most of the extracaldera facies. The remnants of the silicic volcanic cover extend over an area of ~3000 km². Reactivated fracture zones related to the volcanic activity include NW to W- trending faults that reveal a transition from left lateral to right lateral slip as result of a change in the stress field during the last stages of silicic volcanism. These and other groups of N-S to NNW trending faults accommodated the collapse structures and were the sites of emplacement of massive pyroclastic dikes. Immediately north of the Trans Mexican Volcanic Belt, ignimbrites and related rocks of the Mesa Central and southern Sierra Madre Occidental are slightly younger and display a westward 30 to ~15 Ma migration pattern accompanied by E-W regional extension. These patterns have been attributed to the roll back of the subducted slab, which caused the ascent of asthenospheric mantle and probably triggered ignimbrite flare-up. The distinct tectonic and geochronologic patterns of the arc volcanic rocks in the northern Sierra Madre del Sur and the southern Sierra Madre Occidental-Mesa Central suggests two slab segments with different geometry an dynamics during the early Oligocene that were decoupled at the latitude of the Trans Mexican Volcanic Belt.
DE: 8178 Tectonics and magmatism
DE: 8185 Volcanic arcs
DE: 8440 Calderas
DE: 9350 North America
DE: 9604 Cenozoic
SC: Union [U]
MN: 2007 Joint Assembly