Abstract

BAEZ, Walter et al. Stratigraphy and evolution of the Cerro Blanco Volcanic Complex, Puna Austral, Argentina. Rev. mex. cienc. geol [online]. 2015, vol.32, n.1, pp.29-49. ISSN 2007-2902.

Cerro Blanco Volcanic Complex is located in Catamarca Province in the southern limit of Andean plateau. It corresponds to a system of nested calderas, with associated domes and pyroclastic deposits. All erupted products are rhyolitic/rhyodacitic in composition and constitute the youngest (Middle Pleistocene-Holocene) collapse calderas system in the Southern Central Andes based on the available radiometric ages. The Cerro Blanco Volcanic Complex hosts an active, small geothermal field and is subsiding with an average velocity of 0.87 cm/year. Despite the existence of numerous studies on regional volcanism of the southern edge of the Andean plateau, the stratigraphy of most of eruptive centers in the region is poorly understood. This study presents a new stratigraphic scheme for the Cerro Blanco Volcanic Complex using a combination of lithostratigraphic units and Unconformity Bounded Stratigraphic Units, plus the application of volcanic activity units and lithosome concept. The results allowed to reconstruct the Cerro Blanco Volcanic Complex evolution in three main eruptive epochs that constitute an eruptive period: i) the Cortaderas eruptive epoch (Middle Pleistocene) is represented by the homonymous synthem and characterized by explosive boiling over eruptions with the generation of huge volumes of pyroclastic density currents (Barranca Blanca and Carachi ignimbrites). The source of these eruptions remains unknown. ii) The Campo de la Piedra Pómez eruptive epoch (Upper Pleistocene), represented by the homonymous synthem and formed by at least one boiling over, explosive eruption. This eruption had two main eruptive phases represented by synthems UI and UII and was characterized by the generation of huge volumes of pyroclastic density currents (Ignimbrita Campo de la Piedra Pómez). A preliminary model is proposed in which the Campo de la Piedra Pómez eruptive epoch is associated with a volcano-tectonic depression. iii) The Cerro Blanco eruptive epoch (Holocene), represented by the homonymous synthem which includes the pre-, syn- and post-Cerro Blanco Caldera collapse (subsynthems CB1, CB2 and CB3 respectively). The pre-caldera activity was effusive and is indirectly represented by block and ash flow deposits. The syn-caldera activity was explosive with a plinian/subplinian eruptive style with simultaneous pyroclastic density currents generation, represented by Cerro Blanco Ignimbrite and associated pyroclastic fall deposits. The post-caldera activity was effusive/explosive and is represented by post-caldera domes and associated block and ash and vulcanian fall deposits. The results indicate that over the past 100000 years the Cerro Blanco Volcanic Complex had at least two large-scale eruptions (Volcanic Explosivity Index ≥ 6). Particularly, the caldera-forming Cerro Blanco eruption constitutes one of the greatest Holocene volcanic events in the Central Andes. Finally, the results presented in this study could contribute to the evaluation of the potential hazard associated with a possible renewal of explosive activity at Cerro Blanco Volcanic Complex.

Keywords : felsic volcanism; Quaternary; sequential stratigraphy; volcanic hazard; Central Andes.

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