Preliminary Rb/Sr geochronology of calc-alkaline dykes from the Tandilia system, Buenos Aires province, Argentina - Echeveste, H; Ribot, A; Teixeira, Wilson; Fernandez, R; Girardi, Vicente Antonio Vitorio; Piccirillo, Enzo Michele; Bellieni, Giuliano; Jacumin, M (South American Symposium on Isotope Geology, 1997)