Cosmogenic 3He and 21Ne surface exposure dating of young basalts from Southern Mendoza, Argentina

Abstract

Southern Mendoza, Argentina, is characterised by abundant Pleistocene to Holocene volcanism associated with back-arc magmatism, influenced by the subducting Nazca plate. Age determinations in this volcanic area have been improved during the last 5 years. However, there are some volcanic features especially in the Payunia Volcanic Field (PVF) which suggest fairly recent eruptions and which have not been chronologically determined. Recent studies on the Llancanelo Volcanic Field (LLVF) and PVF have determined volcanic activity mainly using K–Ar and 40Ar/39Ar as well as cosmogenic 3He. However, K–Ar and 40Ar/39Ar fail to produce reliable ages in Holocene basaltic flows. To better constrain the younger volcanic activity in the LLVF and especially in the PVF, surface exposure dating using cosmogenic 3He and 21Ne was applied to five volcanic features. By applying this method, 3He and 21Ne ages ranging from late Pleistocene to mid Holocene were obtained for basalts from the area of Los Volcanes, from the PVF. The youngest age acquired is significant as it supports previous evidence for mid Holocene volcanic activity in the PVF and constitutes the first noble gas cosmogenic surface exposure age obtained from a basaltic bomb. This paper illustrates the advantages of using two nuclides (3He and 21Ne) for cosmic-ray exposure ages in the study of recent volcanic eruptions. The results in the present study indicate that the PVF was active in the last 5 ka.