Search

The Štiavnica volcano–plutonic complex is an erosional relic of Miocene caldera-stratovolcano in the Western Carpathians. The complex exposes a vertical section from the volcano basement through subvolcanic intrusions and a ring fault to volcanic edifice, comprising mostly andesitic lava flows and domes. This paper examines internal structure, magnetic fabric as derived from the anisotropy of magnetic susceptibility (AMS), and emplacement dynamics of three intra-caldera andesite domes (referred to as Domes 1–3) located near the presumed ring fault. Magnetic fabrics, carried by multi-domain titanomagnetite and titanomaghemite, are interpreted as recording various mechanisms of dome growth controlled by active caldera collapse. Dome 1 is explained as a lava coulée, fed by conduits located along the ring fault, with a long lava outflow down the sloping caldera floor. Dome 2 represents an elongated, ring fault-parallel dome wherein the lava flowed a short distance over a flat floor. Dome 3 is interpreted as a composite dome fed from multiple linear fissures opened at a high angle to the ring fault. Subsequently, the dome was intruded by ring fault-parallel dikes that may have potentially fed overlying, now largely eroded lava domes and flows. Finally, we suggest that all domes formed during collapse of the Štiavnica caldera and the various mechanisms of their growth reflect different stages of the caldera evolution from piston (Dome 2) through trap-door (Dome 1) to piecemeal (Dome 3). [ABSTRACT FROM AUTHOR]

Abstract: In this paper we present a study of the structural setting of the volcanic island of Ischia by the analysis and interpretation of high-resolution aeromagnetic and self-potential data recently acquired over the island. The magnetic data allowed us to locate the main anomaly sources and lineaments of the island and its offshore surroundings, while the self-potential (SP) data provided information on both the structural pattern of the resurgent caldera and the high-temperature fluid circulation. An inversion of the acquired magnetic and SP data, and a joint modelling of the magnetic data and of a previous gravity data set along a SW–NE profile allowed us to build a model of the island. The model is characterized by the presence of an igneous–very likely trachytic–structure, whose top is located at 1200–1750 m b.s.l. Such a body, possibly formed by several neighbouring intrusions, has a density contrast with the pyroclastic cover of about 0.4 gr/cm3 and its central-western part, below Mt. Epomeo, seems to be demagnetized. The demagnetization should be connected to the high geothermal gradient measured in this portion of the island and may be due to hydro-chemical alteration processes and/or to the possible presence of partially melted spots within the intrusion. Our outcome is consistent with the results of previous geophysical, geo-volcanological and geothermal studies. [Copyright &y& Elsevier]

The western slope of Cerro Domuyo in northern Patagonia is characterized by thermal springs with boiling waters, Quaternary silicic domes, and pyroclastic deposits that suggest the existence of a geothermal reservoir. According to geochemical studies, the reservoir may have a temperature of 220 °C and one of the largest advective heat fluxes reported for a continental volcanic center. In this paper, we propose a more refined conceptual model for the Domuyo geothermal area, based on a geological survey supported by U Pb, U Th, and Ar Ar geochronology and by magnetotelluric and gravity surveys. Our study indicates that the Domuyo Volcanic Complex (DVC) is a Middle Pleistocene dome complex overlying middle Miocene to Pliocene volcanic sequences, which in turn cover: 1) the Jurassic-Early Cretaceous Neuquén marine sedimentary succession, 2) silicic ignimbrites dated at ~186.7 Ma, and 3) the Paleozoic metamorphic basement intruded by ~288 Ma granite bodies. The volcanic cycle in the DVC is distinctly bimodal, characterized by the emplacement of massive silicic domes and less voluminous olivine basalts on its southern slope. A major collapse of the central dome at ~600 ka produced a voluminous (19.4 km3 and 133 km2) block-and-ash flow, and associated pyroclastic flows, that filled a valley to the southwest at distances up to ~30 km from Cerro Domuyo summit. This was followed by a period of intense effusive activity that formed the Cerro Guitarra, Cerro Las Pampas, Cerro Domo, and Cerro Covunco silicic domes. The last two domes are the youngest and largest edifices, dated at 0.50 Ma (Ar Ar age) and 0.25 Ma (U Th age). Pre-Cenozoic successions were affected by N-S reverse and thrust faults that were later displaced by an ENE-WSW-trending transtensional belt. The basement rocks at the northern termination of the Cordillera del Viento anticlinorium were also displaced towards the east-northeast by this belt, which is observed NNW of Cerro Domuyo. The DVC was emplaced within this zone of crustal weakness. The integration of geologic observations with magnetotelluric and gravity data, allowed us to develop an updated conceptual model of the geothermal system. The geothermal reservoir is inferred at a depth of less than 2 km within pre-Pliocene fractured rocks, bounded by ~WSW-ENE trending faults and sealed by the pyroclastic deposits and rhyolitic lavas of the DVC. The location of most thermal springs is not directly controlled by faults. Instead, flows emerge at the contact between the fractured and faulted basement and the caprock. • The Domuyo Volcanic Complex (DVC) is a silicic dome complex formed in the Pleistocene. • The central dome collapsed at ~600 ka producing a voluminous (19.4 km3) pyroclastic deposit. • The youngest domes were emplaced at ~500 ka and 250 ka. • The DVC was emplaced within a ENE-WSW trending transtensional zone of crustal weakness. • The geothermal reservoir is hosted in pre-Pliocene rocks sealed by the DVC pyroclastics and lavas. [ABSTRACT FROM AUTHOR]

This special issue aims to highlight and strengthen the role of geology in modern volcanology, which has grown turbulently in recent years, especially in the field of numerical modelling. Accurate mapping of debris avalanche and lahar deposits was fundamental constraints in simulating lahars along the Negro River and in the upper Amazonia basin (Espin Bedon et al., this volume). Finally, a review paper on use of drones to collect volcanological field data (Jordan, this volume) completes the special issue, showing possibility and potential of this new and rapidly evolving methodology. [Extracted from the article]