Late Archean analogy to modern accretionary plate margins, an example from Superior Province, Canada

New paper recently published in Precambrian Research examines an illustrative example of a Late Archean granitic pluton emplaced along a major tectonic boundary in the Superior Province, northeastern Québec, Canada. To characterize the syn-magmatic strain patterns, we integrate structural and kinematic analysis with anisotropy of magnetic susceptibility (AMS) and numerical modeling of fabric development in response to strain increments. This dataset allowed us to set-up a general geological model that discusses the significance of pluton fabrics, interfering intrusive and tectonic strains, and finally also on evaluating various scenarios for the Late Archean assembly of the Superior Province.

Žák J., Tomek F., Svojtka M., Vacek F., Kachlík V., Ackerman L., Ježek J., Petronis, M.S. (2021): Distributed crustal shortening followed by transpressional shearing in the Superior Province, northeastern Canada: a Late Archean analogy to modern accretionary plate margins? Precambrian Research 362, 106322. (DOI)

Metal(loid)s remobilization from contaminated soils during experimental wildfires

The temperature-dependent releases of metal(loid)s (As, Cd, Cu, Pb, Zn) from biomass-rich savanna soils collected near a Cu smelter in Namibia have been studied under simulated wildfire conditions. For this purpose, new wildfire-simulating setups were introduced. Laboratory single-step combustion experiments (250–850 °C) and experiments with a continuous temperature increase and online ICP-OES detection (25–750 °C) were coupled with mineralogical investigations of the soils, ashes, and aerosols. The results indicate that metals are dominantly concentrating in the ash residue, and part of As is remobilized depending on temperature. Therefore, the active and abandoned mining and smelting sites, especially those highly enriched in As, should be protected against wildfires, which can be responsible for substantial As re-emissions.

Tuhý M., Ettler V., Rohovec J., Matoušková Š., Mihaljevič M., Kříbek B., Mapani B. (2021):  Metal(loid)s remobilization and mineralogical transformations in smelter-polluted savanna soils under simulated wildfire conditions. Journal of Environmental Management 293, 112899. (DOI)

Looking at a Pb–Zn mining/smelting site in Kabwe (Zambia) using tree rings

We used pine tree rings and soil geochemistry to expose the activity of a Pb-Zn smelter in Kabwe, Zambia. We found that local soils are extremely contaminated (up to 16000 mg/kg Pb; 14000 mg/kg Zn; 600 mg/kg Cu in the topsoil). Also, metal bearing particles share their Pb isotopic signature with smelting by-products, and more concerning, metals in tree biomass. We concluded that these metals enter the tree though the bark and leaves, not the roots, implying airborne contamination. Using Pb and C isotopes we mapped the dendrochronology of the tree and verified its susceptibility to changes in smelter production throughout the late 20th century.

Baieta R., Mihaljevič M., Ettler V., Vaněk A., Penížek V., Trubač J., Kříbek B., Ježek J., Svoboda M., Sracek O., Nyambe I. (2021): Depicting the historical pollution in a Pb–Zn mining/smelting site in Kabwe (Zambia) using tree rings. Journal of African Earth Sciences 181, 104246. (DOI)

Plenary talk at the 7th Slag Valorization Symposium

Vojtěch Ettler will give a plenary lecture entitled “The leaching behavior of smelting slags: from contaminants to critical metals” on the 7th International Slag Valorization Symposium (SVS7). The conference, originally planned to take place in Leuven, Belgium, will finally run in a virtual mode. SVS7 is a major event on characterization and applications of metallurgical slags and will bring together people from R&D sector and industry.

Mobility of As in sulfidic gley soils during drought

We combined selective chemical extractions and S isotopes to examine the mobility of As and trace metals (Co, Cu, Ni) in two Czech wetland soils enriched in authigenic Fe-As sulfide minerals through the drying process. We found that As and trace metals released via oxidation of the sulfide phases (particularly Fe sulfides) were almost entirely sequestered by Fe(III) (oxyhydr)oxides, but concomitant acidification resulted in the pH-dependent release of the As(III) and trace metals. Although our results documented the relatively low As mobilization potential under relatively short droughts (several weeks), the preservation of the anoxic conditions must be regarded as a fundamental management strategy of these and other sulfidic wetlands enriched in As.

Drahota P., Peřestá M., Trubač J., Mihaljevič M., Vaněk A. (2021): Arsenic fractionation and mobility in sulfidic wetland soils during experimental drying. Chemosphere 277, 130306. (DOI)

Successful virtual PhD conference

We had a successful virtual conference, which has been jointly organized by PhD students associated to the Center for Geosphere Dynamics (UNCE/SCI/006 project) and SGA Student Chapter Prague. The morning of 15th April 2021 was full of exciting presentations (see program and abstracts here). Thanks go to all participants (we were up to 45), but especially to Rafael Baieta, Marine Jouvent and Marek Tuhý, who organized the conference and chaired individual sessions within the ZOOM platform!

Invasion to Carboniferous lakes makes horseshoe crabs look like babies

Today’s horseshoe crabs are often described as living fossils, mostly for their early appearance in the fossil record and their supposedly conservative morphologies. Nevertheless, after a careful investigation, one can find even peculiar species among this group of spider’s close relatives. Indeed, the recent marine representatives of horseshoe crabs (three genera, four species) are all members of one surviving clade called Limulidae. Deep in the past, during the Paleozoic and Mesozoic, some horseshoe crabs evolved into quite different morphologies and explored various environments. One group called Belinuridae comprises mostly late Paleozoic species that explored freshwater habitats. Lustri, Laibl and Bicknell, in their paper published recently in PeerJ (Lustri et al. 2021), redescribe small (about 3 cm long) and morphologically simple belinurid Prolimulus woodwardi. This species has been originally described by Antonín Frič, back in 1899, from the famous sapropelic coal of the Plzeň Basin. Based on numerous well-preserved specimens, the authors describe and clarify the species morphology, including such details as opercula and chelicerae. Phylogenetic analysis shows that Prolimulus is, together with some other morphologically similar genera, a member of highly paedomorphic (i.e., resembling juvenile stages of others closely related taxa) ingroup within Belinuridae. This discovery is further corroborated by morphometric results and by the fact that there are epibionts attached to some Prolimulus specimens. The presence of attaching organisms on the exoskeleton of Prolimulus suggests, that these small specimens are individuals that already stopped or significantly slowed the molting of their exoskeleton. In other words, they are adults that retain juvenile morphology. Such morphological and developmental plasticity, together with a successful exploration of freshwater habitats illustrates the horseshoe crab’s ability to adapt to various environmental conditions in the deep past.

Lustri L., Laibl L., Bicknell R. 2021. A revision of Prolimulus woodwardi Fritsch, 1899 with comparison to other highly paedomorphic belinurids. PeerJ 9, e10980. (DOI)

Carboniferous eruption covered central and western Bohemia with up to 1 m thick ash layer

The famous Bělka tuff is a widespread pyroclastic layer preserved elsewhere in the central and western Carboniferous late- to post-orogenic basins. This tuff represents a unique stratigraphic marker documented from tens of boreholes and numerous black coal mines within a large area between the southern edge of the Pilsen Basin in western Bohemia to the eastern part of the Kladno-Rakovník Basin over a distance of 100 km. However, its volcanic source was until now unclear. In a new study by Tomek et al. published in International Geology Review, a multidisciplinary approach using the LA-ICP-MS U/Pb zircon dating, thickness and grain size distribution analysis, and volume calculation suggested that the source volcano is the Altenberg–Teplice Caldera located at Czech-German border in the NW Bohemian Massif. In detail, this volcano erupted a major caldera-forming ignimbrite eruption with an estimated volcanic explosivity index 7 (out of 8) at 314 Ma. The pyroclastic density currents travelled over a distance of ca. 60 km towards the area of Oparno valley (Porta Bohemica). From here, the northeastern winds distributed the volcanic ash cloud towards the southwest, where the ash was deposited in the sedimentary basins. The isopach reconstruction indicate that for instance in Regensburg (Germany), there was a 10 cm thick ash layer that originated from the Altenberg–Teplice Caldera nearly 220 km away.

Tomek F., Opluštil S., Svojtka M., Špillar V., Rapprich V., Míková J. (2021): Altenberg–Teplice Caldera sourced Westphalian fall tuffs in the central and western Bohemian Carboniferous basins (eastern Variscan belt). International Geology Review in press. (DOI)