INVESTIGADORES
OTAMENDI Juan Enrique
congresos y reuniones científicas
Título:
The Huincan eruptive cycle, southern Mendoza: an example of andesitic front-arc-like miocene volcanism in the back arc of the Southern Volcanic Zone
Autor/es:
NULLO, F., OTAMENDI, J., _BALDAUF, P., STEPHENS, G.
Lugar:
Mendoza
Reunión:
Congreso; Backbone of the Americas Patagonia to Alaska; 2006
Resumen:
A chain of
monogenetic domes and cones erupted during the Huincan cycle (HC) in the
northern SVZ (34º - 35º Lat. S, 69º 39` Long. W), for more than 100 kilometers.
Ar-Ar amphibole ages range from 10 to 6 Ma. All rocks plot in the sub-alkaline
field, and have a narrow, range of SiO2 (55 to 62 % wt) implying
they are basaltic andesite and andesite. Rock compositions straddle the
boundary between calc-alkaline and tholeiitic sub-series in the FeO*/MgO vs SiO2
diagram, and fall in the medium-K field of the SiO2-K2O
diagram. None of these volcanic rocks is primitive as they are not equilibrated
with any mantle assemblage. Rocks from HC have relative and absolute contents
of trace elements resembling intermediate igneous rocks erupted along magmatic
arc fronts. They are characterized by
depletions in HFSE relative to other incompatible elements. HSFE depletion of
the Huincan rocks is both absolute (compared to primitive mantle) and relative
(compared to LILE and LREE). Since HC rocks appear in a belt far to the east of
the main volcanic arc and were active at the same latitude and time (e.g. Kay
et al., 2005), the HC could be considered a case of back-arc magmatism. A
present-day distance of about 75
km from the volcanic front sequence of the Teniente
Volcanic Complex (TVC) and the chain of HC provides an estimate of the distance
between the fore-arc and the back arc. This minimum distance neglects tectonic
shortening during the last 5 Ma. Comparing the geochemistry of back-arc centers
of HC to rocks of the volcanic front (TVC) having equivalent SiO2 contents,
we note that the abundance of most trace elements is coincident for both these
groups. The Sr and Ba contents of the Huincan rocks are significantly elevated
relative to volcanic arc-front. In HC rocks LREE are slightly above, or overlap
with, the highest values of the volcanic-front lavas. Arc-front lavas have
significantly more Th than back-arc rocks. Despite these differences, there is
a striking resemblance between the HC back-arc and TVC frontal-arc rocks
suggesting that similar petrogenetic processes controlled magmatism in the
arc-front and back-arc, which are separated by tens of kilometers.