Petrogenesis of Miocene volcanic arc rocks over the Chilean- Pampean flat-slab segment of the Central Andes constrained by mineral chemistry



Miocene arc volcanism is manifested widely in the Valle del Cura-El Indio belt region (29°30´–30° South latitude), in the southern Central Andes of Argentina and Chile. The magmas that fed this volcanism are well represented by the Cerro de las Tórtolas Formation, which is divided into two volcanic episodes based on petrographic, chemical and age differences: an older basaltic-andesitic event (16–14Ma) and a younger andesitic to dacitic (13–10Ma) one. Representative plagioclase, orthopyroxene, clinopyroxene and amphibole phenocrysts from rock samples already characterized from geochemical and isotopic viewpoints were selected for electron microprobe determination of mineral chemistry. Results indicate an overall homogeneous composition for each of the mineral phases. Equilibrium temperatures were estimated through two-pyroxenes, amphibole-plagioclase and amphibole geothermometers, which show a consistent temperature range between 970 to 850°C. Equilibrium pressure calculated using amphibole composition for volcanic suites produced the most comprehensive results for pressure equilibrium conditions, with results close to 4kb. Changes in the residual mineral assemblages and variations in isotopic signatures indicate that primary magmas were equilibrated at the lower crust with a gradual increase of crustal thickness. These melts evolved towards intermediate magma chambers, where crystallization of phenocrysts occurred at the same temperature and pressure conditions, hence, no increase in depth of intermediate magma chambers is registered although the increase of crustal thickness registered from Lower to Middle Miocene times.


Andesitic; Geothermobarometry; Volcanisme; Crustal thickness; Valle del Cura; Argentina; Chile

Full Text:




  • There are currently no refbacks.

Creative Commons License
This work is licensed under a Creative Commons Attribution-ShareAlike License.

            Facultat de Ciències de la Terra                       Geociències Barcelona                           Institut de Diagnosi Ambiental                    Universitat Autònoma de Barcelona           
                Universitat de Barcelona                                                                                          i Estudis de l'Aigua (CSIC) 
Geologica Acta (ISSN-1695-6133)
Biblioteca de Ciències de la Terra (UB-CSIC) | Facultat de Ciències de la Terra, Martí i Franquès s/n 08028 Barcelona | Spain
Phone: +34 93 403 19 89 | E-mail:
RCUB RCUB Declaració ètica Avís Legal Centre de Recursos per a l'Aprenentatge i la Investigació Universitat de Barcelona