Year

2014

Degree Name

Doctor of Philosophy

Department

School of Earth and Environmental Sciences

Abstract

The basaltic volcanism occurring on a continental plate behind a volcanic arc is not well studied, as this type of volcanic activity is neither common nor easily classified by conventional tectonic setting. In order to investigate the volcanism of this type, an area with abundant Quaternary monogenetic volcanism behind a volcanic arc was chosen, namely, the Payenia Basaltic Province (PBP), in central west Argentina. The PBP is subdivided into several volcanic fields; Nevado, Payún Matrú, Llancanelo and Rio Colorado. The Quaternary alkali volcanism produced in this region has been the focus of several studies since the 1960s, with the pioneering work of Llambías (1966), mainly dedicated to the polygenetic Payún Matrú caldera. More recently, several studies have dealt with the monogenetic volcanism in the PBP, classifying this setting as back-arc (Bermudez and Delpino, 1989; Bertotto et al., 2009; Gudnason et al., 2012; Jacques et al., 2013; Espanon et al., 2014b; among others), intraplate (Ramos and Folguera, 2011) or a transition between back-arc and intraplate (Søager et al., 2013; Hermando et al., 2014), highlighting the difficulty in assigning a setting. In the last few years, the understanding of this basaltic province has significantly increased; however, there are some aspects and approaches that have not been previously considered and applied. These are, for example; to integrate and compare the geochemical signatures of the volcanic fields composing the PBP, in order to obtain a general geochemical fingerprint. Furthermore, using a combined approach with geochemistry and geochronology, the evolution of the PBP can be reconstructed.

The focus of this investigation is the Llancanelo and the Payún Matrú volcanic fields as they represent the latest stages of activity in the PBP and are late Quaternary in age, according to the available chronology. The aims of the investigation are i) to determine the geochemical signatures that have controlled the volcanism during the Pleistocene and the Holocene, ii) to temporally and spatially determine the volcanic evolution and to comprehend the processes that shaped these two volcanic fields, and iii) to contribute broadly to the understanding of this type of volcanism and thereby relate the findings with similar locations around the globe. In the current investigation, new geochemical data from the Llancanelo Volcanic Field (LLVF) and Payún Matrú Volcanic Field (PMVF) are presented. In addition, new numerical ages from three different dating methods are provided. These ages are from basalts of the Pampas Onduladas flow which have not been previously dated and from the Santa Maria volcano which has been regarded as young (Espanon et al., 2014a), but for which no previous reliable numerical ages were available. Of special interest are the Holocene basalts from the Santa Maria volcano, as they constitute the most recent history of the PBP.

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