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

Estimates of pyroclastic flow emplacement. temperatures in the Cerro Galán ignimbrite and Toconquis. Group ignimbrites were determined using thermal. remanent magnetization of lithic clasts embedded within. the deposits. These ignimbrites belong to the Cerro. Galán volcanic system, one of the largest calderas in the. world, in the Puna plateau, NW Argentina. Temperature. estimates for the 2.08-Ma Cerro Galán ignimbrite are. retrieved from 40 sites in 14 localities (176 measured. clasts), distributed at different distances from the caldera. and different stratigraphic heights. Additionally, temperature. estimates were obtained from 27 sample sites (125. measured clasts) from seven ignimbrite units forming. the older Toconquis Group (5.60–4.51 Ma), mainly. outcropping along a type section at Rio Las Pitas, Vega. Real Grande. The paleomagnetic data obtained by. progressive thermal demagnetization show that the clasts. of the Cerro Galán ignimbrite have one single magnetic. component, oriented close to the expected geomagnetic. field at the time of emplacement. Results show therefore. that most of the clasts acquired a new magnetization. oriented parallel to the magnetic field at the moment of. the ignimbrite deposition, suggesting that the clasts were. heated up to or above the highest blocking temperature. (Tb) of the magnetic minerals (Tb=580°C for magnetite;. Tb=600–630°C for hematite). We obtained similar emplacement. temperature estimations for six out of the seven. volcanic units belonging to the Toconquis Group, with the. exception of one unit (Lower Merihuaca), where we found. two distinct magnetic components. 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. The. homogeneity of high temperatures from proximal to distal. facies in the Cerro Galán ignimbrite provides constraints for. the emplacement model, marked by a relatively low eruption. column, low levels of turbulence, air entrainment, surface–. water interaction, and a high level of topographic confinement,. all ensuring minimal heat loss.