Palaeomagnetism and K-Ar Ages of Cenozoic Basalts from Argentina

Results of a combined palaeomagnetiogeochronological study made on Cenozoic basalts from the extra-Andean area of the Provinces of Mendoza and Neuqutn are presented and discussed in the light of the geological stratigraphy of the area and of the normal and reversed geomagnetic polarity intervals now well established for the past 4 My. The polarities of samples which yielded older dates are compared with the time zones of normal and reversed polarity but with arbitrary (i.e. not absolute) time scales, suggested by sea-floor spreading. It is concluded that the volcanism during the Cenozoic in this area occurred in cycles. The most recent cycle occurred between the Upper Pliocene and the end of the Pleistocene in the north, centre and south of NeuquCn province and in the south of Mendoza province. An older cycle extended from the Upper Miocene until the Middle Pliocene in the south and centre of NeuquCn province. We have defined new boundaries, which we have called GI and G2, between normal and reversed epochs at 5-5+0-3 My (R/N) and a