Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2016 Polycyclic scoria cones of the Antofagasta de la Sierra basin, Southern Puna plateau, Argentina WALTER BA ´ EZ 1*, GERARDO CARRASCO NUN ˜ EZ 2, GUIDO GIORDANO 3,4 , JOSE´ G. VIRAMONTE 1 & AGOSTINA CHIODI 1 1Unidad de recursos geolo´gicos y geote´rmicos INENCO (UNSa – CONICET), Av. Bolivia 5150, A4400FVY Salta, Argentina 2Centro de Geociencias, UNAM Campus Juriquilla, Blvr. Juriquilla 3001 Quere´taro, Qro. 72300 Mexico 3Department of Sciences, University Roma Tre, 00146 Rome, Italy 4CNR-IDPA Institute for Dynamics of Environmental Processes, Via M. Bianco, 20131 Milan, Italy *Correspondence: [email protected] Abstract: Despite a number of published papers focusing on the geodynamic implications of the recent Southern Puna mafic magmatism, there have been fewer studies of the volcanology and stratigraphy of this outstanding volcanism. This paper presents a detailed map of two well- preserved Quaternary scoria cones showing their complex stratigraphy. Complementary morpho- metric, morpho-structural, petrographic and geochemical data were used to reconstruct the evolu- tion of both volcanoes. The occurrence of more than one eruption at each volcano was inferred by the recognition of temporal hiatuses using morpho-stratigraphic criteria. The polycyclic nature of both scoria cones could be related to a combination of a high input magma in response to litho- spheric delamination, a favourable regional stress field and the interaction of rising magma with pre-existing faults. The youngest eruptions in both volcanoes were complex, with shifts in the erup- tive style from violent strombolian to hawaiian /strombolian phases, and probably lasted for a few years. The explosive activity was accompanied by the emission of lava flows from lateral vents. Phreatomagmatic activity was triggered during the waning stages of the eruptions. The occurrence of more than one eruption in a single scoria cone and the changes in the eruptive style during long- lasting eruptions are important topics for volcanic hazard assessment in the Southern Puna. Scoria cones are small monogenetic volcanoes extrusion rates and long-lived volcanic activity produced during eruptions with a broad spectrum (kyr to myr) consisting of periods of quiescence of eruptive styles, including strombolian, violent and erosion (Walker 2000). However, some studies strombolian, hawaiian and phreatomagmatic. Mono- carried out in different geological settings suggest genetic scoria cones are characterized by eruptions that many scoria cones and maars may actually lasting from days and months to several years, involve multiple eruptions separated by tens to involving discrete, small-volume magma batches hundreds of thousands of years with geochemical and associated with dispersed plumbing networks variations (e.g. Turrin & Renne 1987; Renault et al. (Vespermann & Schmincke 2000). Scoria cones 1988; Wells et al. 1990; Bradshaw & Smith 1994; typically occur as fields of small volcanoes together McKnight & Williams 1997; De Benedetti et al. with other monogenetic volcanic structures, such 2008; Sheth et al. 2009; Kereszturi et al. 2010; as maars, tuff rings and lava domes (Connor & Needham et al. 2011; Sheth 2014). In an attempt Conway 2000; Ne´meth 2010) and are usually con- to clarify this paradoxical situation, Ne´meth & trolled by the regional tectonic setting (e.g. Lesti Kereszturi (2015) proposed a new definition for a et al. 2008; Pardo et al. 2009). In contrast, poly- monogenetic volcano: a volcanic edifice with a genetic volcanoes are characterized by more com- small cumulative volume (typically ≤1 km 3) that plex plumbing systems, including the development has been built up by one continuous, or many dis- of relatively large magma chambers in the upper continuous, small eruptions occurring over a short crust. Thus polygenetic volcanoes show complex timescale (typically ≤10 years) and fed from one patterns of compositional variations, higher magma or multiple magma batches through a relatively From: N e´meth, K., C arrasco-N u´n˜ez , G., A randa-G o´mez, J. J. & S mith, I. E. M. (eds) Monogenetic Volcanism. Geological Society, London, Special Publications, 446, http: // doi.org/10.1144/SP446.3 # 2016 The Author(s). Published by The Geological Society of London. All rights reserved. For permissions: http:// www.geolsoc.org.uk/permissions. Publishing disclaimer: www.geolsoc.org.uk /pub_ethics Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2016 W. BA ´ EZ ET AL. simple, closely spaced feeder dyke (and sill) Geological setting system with no associated well-developed magma chamber. In addition, Ne´meth & Kereszturi (2015) The Miocene–Quaternary volcanic activity in the indicated the existence of departures from the Altiplano-Puna plateau originated the Andean monogenetic volcanoes sensu stricto that create a CVZ (ACVZ) (Fig. 1). A north–south volcanic arc nearly continuous spectrum to the polygenetic has developed since Neogene times, initially along volcanoes sensu stricto. One type of ‘transitional’ the Maricunga belts and finally stabilized 50 km to volcano is the polycyclic monogenetic volcano the west in the present day volcanic arc (Western (Kereszturi et al. 2010; Ne´meth & Kereszturi Cordillera) (Kay & Coira 2009; Guzma´n et al. 2015). Such volcanoes are formed by multiple and 2014). The eastwards broadening of arc magmatism complex eruptive episodes with small volumes of along regional NW–SE vertical strike-slip fault magma and separated by time gaps from thousands systems can be explained by shallowing of the to millions of years. Thus the resultant volcanic subducting slab (Viramonte et al. 1984; Viramonte structures show a complex facies architecture, but & Petrinovic 1990; Petrinovic et al. 1999; Riller morphologically resemble the small-volume volca- et al. 2001; Trumbull et al. 2006). The orogen- noes traditionally defined as monogenetic (Ne´meth parallel thrust faults also played an important part & Kereszturi 2015). in focusing the arrest of hydrofractures, the forma- The Southern Puna plateau of Argentina differs tion of magma chambers and the emplacement of from the rest of the Andean Central Volcanic polygenetic volcanoes in the back-arc region (Nor- Zone (CVZ) as a result of the abundance of late ini et al. 2013). Major changes in the magmatic Miocene and younger small mafic (basaltic andes- and deformational style in the Southern Puna back- ite) back-arc volcanic centres (Viramonte et al. arc region began at 7 Ma (Marrett et al. 1994; Kay & 1984; Kay et al. 1994; Risse et al. 2008; Viramonte Coira 2009; Montero Lo´pez et al. 2010; Guzma´n et al. 2010). The presence of this mafic volcanism in et al. 2014). A shift from a purely contractional to the Southern Puna plateau is one of the main a mixed stress regime with normal, strike-slip and arguments supporting late Cenozoic lithospheric thrust faults, and the eruption of both mafic (basaltic delamination beneath this region (Kay et al. 1994; andesite) lavas and the dacitic ignimbrites from Whitman et al. 1996). Despite the publication of Cerro Gala´n Caldera are considered as superficial several papers focused on both the petrogenesis evidence supporting the delamination model pro- and geodynamic implications of this outstanding posed by Kay et al. (1994) for this portion of the magmatism (Knox et al. 1989; Kay et al. 1994; Central Andes. There are currently two different Risse et al. 2008, 2013; Drew et al. 2009; Ducea models that are used to explain the lithospheric et al. 2013; Murray et al. 2015), the stratigraphy delamination below the Southern Puna using the of each volcanic centre and its physical volcanology geochemical features of mafic lavas. The first remains poorly studied. The main aim of this paper model suggests that the mafic magmas were gener- is to contribute to a better volcanological knowledge ated from a relatively homogeneous asthenospheric of the mafic volcanism in the back-arc region of mantle peridotite that upwelled adiabatically and the Southern Puna plateau by performing a detailed melted in the wake of a large foundering block of study of the stratigraphy and geological evolution lower lithosphere (Kay et al. 1994; Risse et al. of two Quaternary scoria cones located in the 2013). The second model proposes that it is not nec- Antofagasta de la Sierra basin: the Alumbrera and essary to catastrophically founder large volumes of De La Laguna (also called Antofagasta) volcanoes. lithosphere to generate the Puna mafic magmas, The stratigraphic criterion in the field survey and but that the small-scale dripping and melting of het- geological mapping was the identification of litho- erogeneous dense lower lithospheric blocks (pyrox- stratigraphic units, including their distribution and enites) are the source of these magmas (Drew et al. stratigraphic relationships. Although no absolute 2009; Ducea et al. 2013; Murray et al. 2015). age is available, some hiatuses in the stratigraphic The Southern Puna back-arc mafic volcanism succession were recognized by significant variations consists of numerous scoria cones, lava domes, in the degree of erosion of each mapped unit. lava flows, tuff rings and maars grouped in small Complementary morphometric, morpho-structural, volcanic fields, one of them located in the Antofa- petrographic and geochemical data were used to gasta de la Sierra Basin (ASB) (Fig. 1). The ASB is reconstruct the evolution of the two volcanoes. a north–south-trending, thrust fault-bounded, intra- The polycyclic nature of both volcanoes and the fac- montane depression. This tectonic depression is tors controlling the variations in the eruptive style closed to the north by the Neogene volcanic chain during a single eruption are discussed and compared Archibarca-Gala´n (Viramonte et al. 1984; Kay & with other mafic volcanic centres of the Southern Coira 2009) and has a floor that dips gently south- Puna plateau and similar well-known historical wards. The sedimentary basin infill is represented eruptions worldwide. by Neogene–Quaternary continental sequences Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2016 POLYCYCLIC SCORIA CONES Fig.