Hawaiian and Strombolian style monogenetic volcanism in the extra-Andean domain of central-west Argentina Gustavo W. Bertotto a, ⁎ , Ernesto A. Bjerg b , Carlos A. Cingolani c a CONICET – Universidad Nacional de La Pampa, Uruguay 151 (6300), Santa Rosa, La Pampa, Argentina b CONICET – Universidad Nacional del Sur, San Juan 670 (8000), Bahía Blanca, Buenos Aires, Argentina c CONICET – Universidad Nacional de La Plata, Calle 1 644 (1900), La Plata, Buenos Aires, Argentina Received 7 November 2005; received in revised form 2 August 2006; accepted 4 August 2006 Available online 20 September 2006 Abstract In the provinces of Mendoza and La Pampa (central-western Argentina), retroarc volcanism was active from the Miocene through historic times. There are approximately 40 basaltic eruptive centers between 36°S and 37°30′S to the East of 68°40′W. These centers were studied in order to define their volcanological evolution. The vents are constituted of seven lithofacies: i.e., (A-1) weakly welded lapilli and bomb beds; (A-2) agglutinated spatter and bomb beds; (A-3) agglutinated spatter beds; (B) ash beds; (C) lava flows; (D) conduit fill; and (E) dikes. Three eruptive episodes (phases) were identified. The first one generated agglutinated spatter and bomb beds (lithofacies A-2), which constitute the internal part of the edifices. These are followed by weakly welded lapilli and bomb beds (lithofacies A-1) and agglutinated spatter beds (lithofacies A-3). The final episode includes lava flows (lithofacies C), minor agglutinated spatter deposits (lithofacies A-3) and isolated lapilli and bomb clasts. We postulate Hawaiian style fountaining activity as responsible for the generation of agglutinated spatter and bombs beds, and variations between Strombolian and Hawaiian activity for the formation of successions of weakly welded lapilli and bomb beds and agglutinated spatter beds. The vent features and the homogeneity of the erupted magma suggest that the studied volcanoes were monogenetic. © 2006 Elsevier B.V. All rights reserved. Keywords: monogenetic volcanoes; basalts; Argentina; Hawaiian; Strombolian 1. Introduction Retroarc basalts (Paleocene–Holocene) from Patago- nia in Argentina form one of the largest Cenozoic continental basaltic provinces on earth (Kay et al., 2004). They constitute the Patagonian Basaltic Province (Llam- bías, 2003) that covers a surface of c. 200,000 km 2 , stretching between 36°S and 52°S. The origin of these basalts has been related to mechanical perturbations of the subcontinental mantle, as a consequence of subduc- tion of the oceanic lithosphere under the South American continental plate (Skewes and Stern, 1979). On the other hand, retroarc magmatism of northern Patagonia (Somuncurá Plateau) has been related to changes in the age of the subducted oceanic crust (Ramos and Barbieri, 1989) and to the presence of transitory hot spots (Kay et al., 1993). An explanation of the origin of the heat necessary to produce the large volume of molten rock Journal of Volcanology and Geothermal Research 158 (2006) 430 – 444 www.elsevier.com/locate/jvolgeores ⁎ Corresponding author. Tel.: +54 2954 436787; fax: +54 2954 432535. E-mail address: gwbertotto@yahoo.com.ar (G.W. Bertotto). 0377-0273/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jvolgeores.2006.08.001