Ústav geotechniky
Browse
Recent Submissions
- ItemThe Fagradalsfjall and Sundhnúkur Fires of 2021-2024: A single magma reservoir under the Reykjanes Peninsula, Iceland?(WILEY, 2024-07-02) Troll, Valentin R.; Deegan, Frances M.; Thordarson, Thor; Tryggvason, Ari; Krmíček, Lukáš; Moreland, William M.; Lund, Björn; Bindeman, Ilya N.; Höskuldsson, Ármann; Day, James M. D.The Reykjanes Peninsula (RP) hosts several volcanic lineaments that have been periodically active over the last 4000 years. Since 2021, following a ca. 800-year quiescence, eight eruptions have occurred on the RP, with more expected in the future. To better understand the origins of this renewed volcanism and help forecast future eruptions, we examine (i) if the ongoing volcanism is fed from a single or multiple magma storage zone(s) or from several smaller reservoirs and; (ii) where the zone(s) are located (i.e. mantle or lower or upper crustal depths). Using major and trace element geochemistry, oxygen isotopes, and seismic tomography we rule out a single, RP-scale, deep-seated magma storage zone. Instead we propose the presence of a ca. 10-km-wide region of crustal-level (9-12 km) magma accumulation beneath the Fagradalsfjall volcanic lineament that fed both the 2021-23 eruptions of the Fagradalsfjall Fires and the 2023-24 eruptions of the Sundhn & uacute;kur Fires.
- ItemUpper Cretaceous to Pleistocene melilitic volcanic rocks of the Bohemian Massif: petrology and mineral chemistry(Slovak Academy of Sciences, 2015-06-15) Roman, Skála; Ulrych, Jaromír; Ackerman, Lukáš; Krmíček, Lukáš; Fediuk, Ferry; Balogh, Kadosa; Hegner, ErnstUpper Cretaceous to Pleistocene volcanic rocks of the Bohemian Massif represent the easternmost part of the Central European Volcanic Province. These alkaline volcanic series include rare melilitic rocks occurring as dykes, sills, scoria cones and flows. They occur in three volcanic periods: (i) the Late Cretaceous to Paleocene period (80–59 Ma) in northern Bohemia including adjacent territories of Saxony and Lusatia, (ii) the Mid Eocene to Late Miocene (32.3–5.9 Ma) period disseminated in the Ohře Rift, the Cheb-Domažlice Graben, Vogtland, and Silesia and (iii) the Early to Late Pleistocene period (1.0-0.26 Ma) in western Bohemia. Melilitic magmas of the Eocene to Miocene and Pleistocene periods show a primitive mantle source [(143Nd/144Nd)t = 0.51280–0.51287; (87Sr/86Sr)t = 0.7034–0.7038)] while those of the Upper Cretaceous to Paleocene period display a broad scatter of Sr-Nd ratios. The (143Nd/144Nd)t ratios (0.51272–0.51282) of the Upper Cretaceous to Paleocene rocks suggest a partly heterogeneous mantle source, and their (87Sr/86Sr)t ratios (0.7033-0.7049) point to an additional late-to post-magmatic hydrothermal contribution. Major rock-forming minerals include forsterite, diopside, melilite, nepheline, sodalite group minerals, phlogopite, Cr-and Ti-bearing spinels. Crystallization pressures and temperatures of clinopyroxene vary widely between ~1 to 2 GPa and between 1000 to 1200 °C, respectively. Nepheline crystallized at about 500 to 770 °C. Geochemical and isotopic similarities of these rocks occurring from the Upper Cretaceous to Pleistocene suggest that they had similar mantle sources and similar processes of magma development by partial melting of a heterogeneous carbonatized mantle source.
- ItemExperimental study on time dependent behaviour of coarse aggregate concrete mixture for 3D construction printing(Elsevier, 2023-04-20) Vespalec, Arnošt; Podroužek, Jan; Boštík, Jiří; Miča, Lumír; Koutný, DanielThis experimental study analyses coarse aggregate-containing and coarse aggregate-free materials from the perspective of additive manufacturing. The primary objective is to identify, through a series of experiments, the fundamental equations that characterise material behaviour at early ages in order to formulate a digital material model. During the research, a previously unreported phenomenon, namely the contradictory development of Young's modulus and cohesion, was observed. In addition, the sensitivity of buildability to changes in material properties was discussed and demonstrated with a motivating example using a spatiotemporal simulation of 3Dprinted concrete.
- ItemLead isotope evolution of the Central European upper mantle: Constraints from the Bohemian Massif(CHINA UNIV GEOSCIENCES, BEIJING, 2020-05-15) Krmíčková, Simona; Krmíček, Lukáš; Romer, Rolf L.; Ulrych, JaromírThe Pb isotope composition of the upper mantle beneath Central Europe is heterogeneous due to the subduction of regionally contrasting material during the Variscan and Alpine orogenies. Late Variscan to Cenozoic mantle-derived melts allow mapping this heterogeneity on a regional scale for the last ca. 340 Myr. Late Cretaceous and Cenozoic anorogenic magmatic rocks of the Bohemian Massif (lamprophyres, volcanic rocks of basanite/tephrite and trachyte/phonolite series) concentrate mostly in the Eger Rift. Cretaceous ultramafic lamprophyres yielded the most radiogenic Pb isotope signatures reflecting a maximum contribution from metasomatised lithospheric mantle, whereas Tertiary alkaline lamprophyres originated from mantle with less radiogenic Pb-206/Pb-204 ratios suggesting a more substantial modification of lithospheric source by interaction with asthenospheric-derived melts. Cenozoic volcanic rocks of the basanite/tephrite and trachyte/phonolite series define a linear mixing trend between these components, indicating dilution of the initial lithospheric mantle signature by up-welling asthenosphere during rifting. The Pb isotope composition of Late Cretaceous and Cenozoic magmatic rocks of the Bohemian Massif follows the same Pb growth curve as Variscan orogenic lamprophyres and lamproites that formed during the collision between Laurussia, Gondwana, and associated terranes. This implies that the crustal Pb signature in the post-Variscan mantle is repeatedly sampled by younger anorogenic melts. Most Cenozoic mantle-derived rocks of Central Europe show similar Pb isotope ranges as the Bohemian Massif.
- Item(40)A/Ar-39 step-heating dating of phlogopite and kaersutite megacrysts from the Zelezna hurka (Eisenbuhl) Pleistocene scoria cone, Czech Republic(Earth Science Institute, Slovak Academy of Sciences, 2020-08-15) Krmíček, Lukáš; Timmerman, Martin J.; Ziemann, Martin A.; Sudo, Masafumi; Ulrych, Jaromír(40)A/Ar-39 step-heating of mica and amphibole megacrysts from hauyne-bearing olivine melilitite scoria/tephra from the Zelezna hurka yielded a 435 +/- 108 ka isotope correlation age for phlogopite and a more imprecise 1.55 Ma total gas age of the kaersutite megacryst. The amphibole megacrysts may constitute the first, and the younger phlogopite megacrysts the later phase of mafic, hydrous melilitic magma crystallization. It cannot be ruled out that the amphibole megacrysts are petrogenetically unrelated to tephra and phlogopite megacrysts and were derived from mantle xenoliths or disaggregated older, deep crustal pegmatites. This is in line both with the rarity of amphibole at Zelezna hurka and with the observed signs of magmatic resorption at the edges of amphibole crystals.