K-Ar and Rb-Sr geochronology and evolution of the Štiavnica Stratovolcano (Central Slovakia)

Abstract

Abstract:The Štiavnica Stratovolcano in Central Slovakia is the largest volcano in the Neogene to Quaternary Carpathian volcanic arc. A large caldera, an extensive subvolcanic intrusive complex and a resurgent horst with late stage rhyolite volcanites are the most characteristic features. The results of new K-Ar and Rb-Sr isotope dating using more sophisticated methodical approaches have changed our view on the timing of volcanic and intrusive activity. K-Ar dating of groundmass fractions combined with Rb-Sr isochron dating in the cases of possible rejuvenation has provided highly reliable results. The lifespan of the stratovolcano is apparently shorter than assumed earlier. Evolution of the stratovolcano took place in five stages during the Early Badenian to beginning of Early Pannonian time: (1) construction of the extensive andesite stratovolcano during the interval 15.0-13.5 Ma; (2) denudation of the volcano concluded with the initial subsidence of a caldera and the contemporaneous emplacement of a subvolcanic intrusive complex of diorite, granodiorite, granodiorite porphyries and quartz-diorite porphyries during the interval 13.5-12.9 Ma; (3) subsidence of the caldera and its filling by differentiated andesites during the interval 13.1-12.7 Ma -volcanic activity overlapping with the emplacement of the youngest intrusions; (4) renewed explosive and effusive activity of less differentiated andesites during the interval 12.7-12.2 Ma; (5) uplift of the resurgent horst in the central part of the caldera accompanied by rhyolite volcanic/intrusive activity during the interval 12.2-11.4 Ma. Extensive epithermal mineralization was contemporaneous with the uplift of the resurgent horst and rhyolite volcanic activity and continued till 10.7 Ma.

Rapid cooling and geospeedometry of granitic rocks exhumation within a volcanic arc: A case study from the Central Slovakian Neovolcanic Field (Western Carpathians)

“…(c) Geological scheme of the central–caldera part of Š tiavnica Stratovolcano. Modified from Chernyshev et al () and Konečný et al (), with indication of andesite extrusive domes AD ‐1, AD ‐2, AD ‐3 according Tomek et al (2016)…”

“…The southern border of the CSNF is built by two smaller volcanoes like Čelovce and Lysec, with volcano‐sedimentary epiclastics transition to adjacent area (Figure (b)). Detailed description of the structure and evolutionary stages of the Štiavnica Stratovolcano can be found in V. Konečný et al (, , , , ), Lexa et al () and Chernyshev et al (). The main structural units of the stratovolcano correspond to the following five evolutionary stages the definition of which is based on superposition and major unconformities established by geological mapping and sporadic biostratigraphic data (see V. Konečný et al, , , , ): The first pre‐caldera stage represents the lower structural unit and products of an andesitic volcanic activity that lie directly on the pre‐Neogene basement, pre‐volcanic sedimentary rocks and consist of biotite‐amphibole‐pyroxene andesites and andesite porphyry. The second stage produced the subvolcanic/intravolcanic intrusive complexes that were emplaced during a break in volcanic activity, represented by the studied granitic rocks. The third caldera stage as the middle structural unit is formed by differentiated volcanic rocks of biotite–hornblende andesite to dacite composition, filling the caldera and paleovalleys on the slopes of the stratovolcano. The fourth post‐caldera stage is represented by the upper structural unit and products of an andesitic volcanic activity. The fifth stage is represented by the so called Jastrabá Formation that comprises products of a late‐stage rhyolitic volcanic activity associated with the uplift of the resurgent horst. …”

“…Continuing subduction was compensated locally by asthenospheric mantle upwelling in the back arc realm. The timing and spatial distribution of the arc‐type andesite volcanics is well represented by the evolution of the CSNF (Chernyshev et al, ; V. Konečný et al, ; Lexa, et al, ). Volcanic activity began by the garnet‐bearing andesites prior to the evolution of the Štiavnica Stratovolcano in the time interval 16.0 Ma 14.8 Ma (Langhian−Early Badenian).…”

“…The stratovolcano reached a diameter of 35–40 km at the base of the volcanic cone and a probable elevation of 3000–4000 m (V. Konečný et al, , ). Creation of the stratovolcano was followed by a period of denudation and emplacement of the extensive subvolcanic intrusive complex of diorite, diorite porphyry, granodiorite, and granodiorite porphyry over the time interval 13.5 Ma to 12.9 Ma (Serravalian–Late Badenian) according to V. Konečný et al (, ) and Chernyshev et al (). However, our study reveals the affinity of dioritic rocks to the earlier stage, and only granodiorites fit with this second stage.…”

“…Although the relative age and the succession of volcanic formations, subvolcanic intrusive rocks and associated metallogenetic processes is relatively well established based on field observations, structural and geochemical data (Koděra, Lexa, Rankin, & Fallick, ; V. Konečný, Lexa, & Planderová, ; V. Konečný et al, ; Lexa, Štohl, & Konečný, ; Pécskay et al, ), the accurate and precise absolute timing and duration of magmatic events and related hydrothermal activity remain uncertain. Existing biostratigraphic data from CSNF, including extensive palynology records (V. Konečný et al, ; Planderová, ), and available isotope dating results are often incongruous due to persisting problems with chronostratigraphic assignment of lithostratigraphic units, correlations of Paratethys stratigraphic stages with isotope ages, complexity of isotope data interpretation in areas with repeated magmatic activity and hydrothermal alterations, and also due to a rather questionable quality of some of the old radiometric data (Chernyshev et al, ; and citations therein). For instance, Bouloton and Paquette () reported zircon crystals armoured in garnet from the Neogene andesites and dacite lavas of CSNF and dated them by Laser Ablation–Inductively Coupled Plasma–Mass Spectrometry (LA–ICP–MS) U–Pb to 13.3 ±0.1 Ma and 12.4 ±0.2 Ma, which is at least 3 Myr younger than previously thought on the basis of whole rock K–Ar and amphibole fission‐track dating coupled with biostratigraphic correlations (V. Konečný, Bagdasarjan, & Vass, ; V. Konečný et al, ; Repčok, ).…”