The
role played by the
regional tectonics and
relationships between volcanic st
ructu
res and thei
r shallow magmatic feeding system a
re of pa
ramount impo
rtance in unde
rstanding multiple late
ral collapse events and, thus, fo
r haza
rd assessment in active volcanoes. Ollag
xfc;e (21°18′S, 68°11′W, Andean Cent
ral Volcanic Zone, Chile-Bolivia bo
rde
r) is an active, andesite-dacite, composite volcano developed on a
regional NW-st
riking extensional fault system that bisects the volcanic edifice. Geological and st
ratig
raphic studies on the summit pa
rt of the cone, togethe
r with new
40A
r/
39A
r dating and pet
rog
raphic and geochemical (majo
r-t
race elements) analyses, have allowed us to delineate the volcanic histo
ry of Ollag
xfc;e and
recognize multiple defo
rmation and late
ral collapse events. The evolution of Ollag
xfc;e appea
rs to be cha
racte
rized by fou
r stages of volcano building, sepa
rated by th
ree main events of defo
rmation of the cone. These defo
rmation events developed p
rog
ressively by downth
row of the SW secto
r of the volcano (
![]()
rc="http://www.sciencedi
rect.com/scidi
rimg/entities/223c.gif" alt="not, ve
rt, simila
r" title="not, ve
rt, simila
r" bo
rde
r="0"> 800 ka), along the NW-st
riking no
rmal fault p
ropagating f
rom the subst
rate, to a final catast
rophic failu
re (
![]()
rc="http://www.sciencedi
rect.com/scidi
rimg/entities/223c.gif" alt="not, ve
rt, simila
r" title="not, ve
rt, simila
r" bo
rde
r="0"> 300 ka) of the SW secto
r and deb
ris avalanche emplacement. Both NW-t
rending
regional tectonics and weakness of the edifice caused by the successive defo
rmation and collapse events a
re
responsible fo
r both the geomet
ric va
riations of the shallow magma feeding system and the coexistence of summit and pa
rasitic dacitic vents. Cent
ral and late
ral vents shifted in a SW-t
rending di
rection, i.e. pe
rpendicula
r to the tectonic t
rend and along the axis of the collapse movement, and developed along a NW-t
rending alignment, i.e. pa
rallel to the main tectonic t
rend and collapse sca
rps.