Geochemical homogeneity of a long-lived, large silicic system; evidence from the Cerro Galán caldera, NW Argentina

Abstract

By applying a number of analytical techniques across a spectrum of spatial scales (centimeter to micrometer) in juvenile components, we show that the Cerro Galán volcanic system has repeatedly erupted magmas with nearly identical geochemistries over >3.5 Myr. The Cerro Galán system produced nine ignimbrites (∼5.6 to 2 Ma) with a cumulative volume of >1,200 km 3 (DRE; dense rock equivalent) of calc-alkaline, high-K rhyodacitic magmas (68-71 wt.% SiO 2 ). The mineralogy is broadly constant throughout the eruptive sequence, comprising plagioclase, quartz, biotite, Fe-Ti oxides, apatite, and titanite.

High-temperature emplacement of the Cerro Galán and Toconquis Group ignimbrites (Puna plateau, NW Argentina) determined by TRM analyses

“…The estimation of emplacement temperatures in this latter case is constrained at 580-610°C, which are lower than the other ignimbrites. These estimations are also in agreement with the lowest pre-eruptive magma temperatures calculated for the same unit (i.e., 790°C; hornblende-plagioclase thermometer; Folkes et al 2011b). We conclude that the Cerro Galán ignimbrite and Toconquis Group ignimbrites were emplaced at temperatures equal to or higher than 620°C, except for Lower Merihuaca unit emplaced at lower temperatures.…”

“…In the same site, clasts with higher temperatures belonging to class A were probably heated at vent before being incorporated in the pyroclastic flow, preserving very high temperature at emplacement. In agreement with temperature estimations of the Lower Merihuaca emplacement are those related to magma preeruptive temperatures calculated by Folkes et al (2011b). The authors have estimated pre-eruptive temperatures for all the outcropped ignimbrites (i.e., Cerro Galán, Cueva Negra and Toconquis Group ignimbrites) applying different geothermometers.…”

“…The regional stratigraphy, described in early works by Francis et al (1983) and Sparks et al (1985), was recently revised (see Folkes et al 2011a) and is summarized in Table 1. Nine distinct outflow ignimbrites are recognized, including two newly identified ignimbrite units in the Toconquis Group (Pitas and Vega ignimbrites).…”

“…The seven ignimbrites belonging to the Toconquis Group (biotite 40 Ar/ 39 Ar age of 5.60-4.51 Ma; Folkes et al 2011a) are best exposed in a 200-m section at Rio Las Pitas locality, Vega Real Grande section (Fig. 2a).…”

“…The currently preserved areal extent of the Toconquis Group ignimbrites is about 420 km 2 , with a total volume of 651 km 3 (DRE). The highly welded Cueva Negra unit (biotite 40 Ar/ 39 Ar age of 3.77±0.08 Ma; Folkes et al 2011a), outcropping on the eastern flanks of the caldera, is not investigated in this study.…”