Torta domes as part of a new morphological and rheological classification based on the distribution of Quaternary domes in the Central Volcanic Zone of the Andes, northern Chile

Abstract

Northern Chile has numerous effusive monogenetic events, among those domes without a morphological or rheological classification. This study analyzes 44 Quaternary domes (0–2.58 Ma) in the Central Volcanic Zone of the Andes (CVZA) using 57 radioisotopic ages (KAr and ArAr) and geochemical data to define their distribution and establish a morphological-rheological classification focusing on torta-type domes. We employed i) compilation of published data, ii) k-means multivariable analysis to identify distribution patterns, and iii) morphometric calculations using MORVOLC to obtain physical parameters. We identified three geographical clusters (GC1, GC2, GC3) and four age clusters (AC1, AC2, AC3, AC4). The first one, GC1 (18.07°-19.79°S) comprises 11 domes, predominantly andesitic, with their activity in the last 700 ka; GC2 (21.21°-23.83°S) includes 25 domes, mainly dacitic, across the entire Quaternary. Finally, GC3 (25.99°-27.11°S) contains eight domes with dacitic and rhyolitic compositions, across the entire Quaternary. The morphological analysis contrasted two classifications: i) based only on morphology, and ii) based on rheology and morphology. In this way, we obtained 27 low lava domes, 10 coulées, and 7 “tortas,” a subtype of low lava dome. Torta domes in northern Chile are restricted to 19.5°-22.5°S and the last ∼400 ka, exhibit specific morphometric characteristics (circular and flat-topped): yield strength (τ₀) between 2.1E+05 and 7.5E+05 Pa, height/radius (H/R) ratio of 0.14–0.27, a mean flank slope of 16.78 to 25.93°, and a pre-eruptive angle surface between 2.96 and 6.72°. The spatial distribution and composition of these domes are related to the geological setting in the area, such as the Altiplano-Puna Volcanic Complex (APVC), the Altiplano-Puna Magma Body (APMB), and local/regional fault systems. This detailed analysis enhances our understanding of Quaternary monogenetic volcanism in the CVZA, providing valuable insights into magmatic evolution, eruption dynamics, morphological structures, and potential volcanic hazards associated in the region. The proposed classification scheme for torta-type domes may be applicable to similar volcanic features worldwide with defined rheological and morphological parameters.