Journal of GEOsciences Table of Contents for the Journal of GEOsciences. List of articles from the latest print issue.http://www.jgeosci.orgen-US Journal of GEOscienceshttp://www.jgeosci.org/img-system/jgeosci_cover.jpghttp://www.jgeosci.org <![CDATA[ Foreword to the thematic set arising from the international conference "Basalt 2017" ]]> Magna T, Rapprich V, van Wyk de Vries B; Vol. 63, issue 4, pages 293 - 294
The Basalt meetings are particularly, but not solely, focused on extensive Cenozoic magmatism and volcanism across Europe and beyond from a multi-faceted perspective of all relevant disciplines of geosciences. These include physical volcanology, mineralogy, petrology, geochemistry, geophysics, stratigraphy with palaeontology, geohazards and geoheritage. The main goals of these meetings include presentation of new discoveries and developments in the understanding of within-plate alkaline magmatism as well as bringing together to a small meeting scientists with distinctly diverse fields of expertise. This melting pot serves as stew for new, non-conformist ideas and becomes a topical platform for fostering a truly inter-disciplinary research.
Following the successful Basalt 2013 meeting held in Görlitz, Germany, the Basalt 2017 conference (http://basalt2017.geocon.cz) was set in the historical town of Kadaň, Czech Republic, on September 18-22, 2017. The conference site was selected due to its historical and picturesque centre and also its location in the north-eastern foothills of the Doupovské Hory Volcanic Complex. Kadaň, surrounded by fabulous volcanic landscapes, provided a good starting point for pre- and post-conference field-trips as well as mid-conference guided walk. The meeting was attended by over 40 participants from ten countries, who presented the results of geochemical, petrological, volcanological, geophysical and paleontological studies of within-plate alkaline volcanic systems and lithospheric mantle. Several contributions also reached out to geoheritage and geohazards. Special attention was paid to the role of Central European volcanology in the development of Earth Sciences in the past centuries. ]]>
http://www.jgeosci.org/rss.php?ID=jgeosci.277 Editorial http://www.jgeosci.org/rss.php?ID=jgeosci.277
<![CDATA[ The origin of the term ’basalt’ ]]> Tietz O, Büchner J; Vol. 63, issue 4, pages 295 - 298
’Basalt’ is a commonly and widely used word. This rock name is important in classification of volcanic rocks (e.g., TAS, QAPF; Le Maitre 2002) and ranks among the most frequent terms used in geology, including planetary science. However, probably no geologist ever started to think where this term actually comes from. On the occasion of the Basalt 2017 conference held in Kadaň (Czech Republic) and the investigation of the Stolpen Volcano (see Tietz et al. 2018, in this issue), the history of the word ’basalt’ was examined more closely. The term was coined in 1546 by Georgius Agricola (1494-1555) in a short caption in De Natura Fossilium - an early modern era text representing the first attempt to scientifically classify minerals, rocks and fossils - referring to ’ash-grey marbles ’ at the Stolpen Castle Hill near Dresden (Saxony, Eastern Germany):
“Some marbles are iron-coloured. This is the basalt that the Egyptians found in Ethiopia. Behind him the Meissner does not stand, either in the colour - he is particularly ferruginous - nor in hardness, which is so great that in the forge use him as an anvil. The Stolpen Castle of the Bishop of Meißen is built on this basalt. The columns are angular.” (Agricola 1546, p 310; Fig. 1, translated from Latin in English). ]]>
http://www.jgeosci.org/rss.php?ID=jgeosci.273 Editorial http://www.jgeosci.org/rss.php?ID=jgeosci.273
<![CDATA[ The Stolpen Volcano in the Lausitz Volcanic Field (East Germany) - volcanological, petrographic and geochemical investigations at the type locality of basalt ]]> Tietz O, Büchner J, Lapp M, Scholle T; Vol. 63, issue 4, pages 299 - 315
The ˜30 Ma Stolpen Volcano near Dresden (Saxony) is situated at the western margin of the Lausitz Volcanic Field. It forms a small isolated basaltic hill, the famous Stolpen Castle Hill, penetrating the granodioritic basement of the Lausitz Block and is worldwide the type locality for the term ’basalt’, as coined by Agricola (1546). The volcano has always been interpreted as subvolcanic crypto- or lava dome.
New geological mapping, dip measurements of the basaltic columnar jointing and the first evidence of scoria for the Stolpen Volcano allow for a new interpretation of the volcanic edifices. On this basis the structure is best described as a maar crater volcano filled by a 110 m thick basanitic lava lake. According to genetic classification, it is a complex monogenetic volcano formed in three phases: (1) a phreatomagmatic diatreme phase with a maar crater, (2) a scoria cone phase with the final basanitic lava lake filling, and (3) a post-volcanic phase with neotectonic uplift, denudation and exposure of a basaltic hill since c. 1.3 Ma. The volcano reconstruction indicates an ongoing change in the eruption style from phreatomagmatic (phase 1) to eruptive and, finally, effusive processes (phase 2) without significant gaps between the eruption episodes. The only difference appears to be caused by a variable water supply during the magma ascent and volcanic eruption.
New mineralogical (QAPF) and geochemical (TAS) investigations of the Stolpen lava samples reveal that the Stolpen Hill is not built by a basalt, but basanite trending toward a nephelinite, following the recent nomenclature. Microscopic analyses also provide evidence of magma mingling, such as nephelinite melt enclaves, and show local lava contamination by the country-rock granodiorite, also supported by the presence of quartz xenocrysts. The combined field observations, petrography and geochemical data indicate overall heterogeneity of the Stolpen lava. Therefore, the Stolpen Castle Hill is not - in a scientific sense - a suitable type locality for either basalt or basanite. However, the outcropping volcanic rocks as well as their scientific and historical importance undoubtedly give relevance to Stolpen as a type locality for basaltic volcanic rocks in a broader sense. ]]>
http://www.jgeosci.org/rss.php?ID=jgeosci.275 Original paper http://www.jgeosci.org/rss.php?ID=jgeosci.275
<![CDATA[ Petrology of weakly differentiated alkaline, high-level intrusive rocks in the Zahořany-Chotiněves Belt near Litoměřice (Czech Republic) ]]> Mysliveček J, Rapprich V, Kochergina YV, Magna T, Halodová P, Pécskay Z, Poňavič M; Vol. 63, issue 4, pages 317 - 331
Weakly differentiated rocks such as basaltic trachyandesites occur rather rarely in the Cenozoic České Středohoří Volcanic Complex (Central Europe, Czech Republic). We present mineralogical, petrological and geochemical data for a basaltic trachyandesite sill located at the southern margin of the České Středohoří Volcanic Complex, where several smaller hills form a quasi-continuous belt between villages of Zahořany and Chotiněves. Uniform petrography and chemical composition provide compelling evidence that all individual outcrops form a single large sill, probably with the exception of the westernmost occurrence at the Křemín Hill. The sill is almost 5 km long (SW-NE) and probably up to 3 km wide (NW-SE). The elongated shape of the sill and its position suggest that the basaltic trachyandesite magma ascended along the Litoměřice Fault forming the south-eastern edge of the NE-SW trending Ohře (Eger) Rift.
The studied rocks are basic and alkali-rich (49.5-50.3 wt. % SiO2, sum K2O + Na2O = 7.8-8.1 wt. %), but their silica contents (volatile-free) approach the boundary of the intermediate domain. This correlates with low concentrations of compatible trace elements such as Cr (15-23 ppm). Their limited degree of differentiation is reflected by smooth chondrite-normalized REE patterns (LaN/YbN = 18.2-19.3) with the absence of any significant Eu and/or MREE anomaly. The incompatible trace-element contents (Sr = 920-1080 ppm, Ba = 840-950 ppm, ƩREE = 280-330 ppm) typify weakly differentiated alkaline volcanic rocks within the Ohře Rift. Based on the chemical composition we suggest that these basaltic trachyandesites belong to the České Středohoří Volcanic Complex rather than to MgO-poor foidites of the Central Bohemia Volcanic Field. The intrusive age of the sill has been determined using conventional whole-rock K-Ar method at 29.12  0.63 Ma (1σ). The initial Sr-Nd isotope compositions (87Sr/86Sri = 0.7048, 143Nd/144Ndi = 0.51270), compare well with existing data for the České Středohoří trachybasalts and attest to their common origin. The single large Zahořany-Chotiněves sill partly fills the apparent gap in the differentiation trend between basanites to trachybasalts and trachyandesites to phonolites reported for the alkaline volcanism of the České Středohoří Mts. ]]>
http://www.jgeosci.org/rss.php?ID=jgeosci.278 Original paper http://www.jgeosci.org/rss.php?ID=jgeosci.278
<![CDATA[ The characterization of sunburn basalts and their magnetic and petrographic properties ]]> Nováková L, Schnabl P, Büchner J; Vol. 63, issue 4, pages 333 - 344
Sunburn texture, a white-grey mottling of dark grey basalts, is frequently found in outcrops around the world. Sunburn basalt is more fractured and less resistant than fresh basalt, and so its identification is of interest in all types of basalt quarries.
Three localities were chosen with different types and shapes of volcanic bodies in the Lausitz Volcanic field in the border area of the Czech Republic and Germany (Borská Skalka, Mittelherwigsdorf, Wittgendorf), in order to characterize sunburn lavas and study the petrographic and magnetic changes between fresh massive and sunburn basalts. The sunburn basalts have cracked, disrupted outcrop surfaces where white-grey spots are observed. As seen in thin section, the spots contain mainly analcite, the mineral that is responsible for the sunburn effect. The appearance of analcite is indicated by the enhanced amount of Al and Na. The whole rock is affected by many cracks that are filled with limonite. Limonite also infiltrates the sunburn spots, which are rich in microcracks.
In the field were measured thirteen profiles perpendicular to the volcanic bodies in order to describe the magnetic properties in situ (magnetic field intensity, inclination and declination values). The intensity of magnetic field and its azimuth change with the distance from the rock. A major change occurs c. 130 cm away from the wall, which implies that the major cause is at some distance. The changes in magnetic inclination were negligible with the exception of the Borská Skalka site, where standard deviation of the magnetic field was 29.3 µT, and the standard deviation of the azimuth 78.7° for the sunburn part. In the laboratory were measured natural magnetic resistivity (NMR) and isothermal remanent magnetization (IRM). The calculated REM (remanent magnetization) parameter averaged 2.0 % for the sunburn parts and 0.8 % for the massive basalt. The sunburn basalts are affected mainly by weathering and hydration that causes changes in petrophysical and magnetic properties. The most prominent changes in all the variables could be seen at Borská Skalka, whose top is exposed to lightnings. Because of the increased conductivity, the sunburn parts become preferred lightning paths and the initial magnetic properties of the basalt can be overprinted by the electrical activity. ]]>
http://www.jgeosci.org/rss.php?ID=jgeosci.274 Original paper http://www.jgeosci.org/rss.php?ID=jgeosci.274
<![CDATA[ Geochemical characteristics of the Late Proterozoic Spitz granodiorite gneiss in the Drosendorf Unit (Southern Bohemian Massif, Austria) and implications for regional tectonic interpretations ]]> Lindner M, Finger F; Vol. 63, issue 4, pages 345 - 362
The Spitz Gneiss, located near the Danube in the southern sector of the Variscan Bohemian Massif, represents a ˜13 km² large Late Proterozoic Bt ± Hbl bearing orthogneiss body in the Lower Austrian Drosendorf Unit (Moldanubian Zone). Its formation age (U-Pb zircon) has been determined previously as 614 ± 10 Ma. Based on 21 new geochemical analyses, the Spitz Gneiss can be described as a granodioritic I-type rock (64-71 wt. % SiO2) with medium-K composition (1.1-3.2 wt. % K2O) and elevated Na2O (4.1-5.6 wt. %). Compared to average granodiorite, the Spitz Gneiss is slightly depleted in Large-Ion Lithophile (LIL) elements (Rb 46-97 ppm, Cs 0.95-1.5 ppm), Sr (248-492 ppm), Nb (6-10 ppm), Th (3-10 ppm), the LREE (e.g. La 10-30 ppm), Y (6-19 ppm) and first row transitional metals (e.g. Cr 10-37 ppm). The Zr content (102-175 ppm) is close to average granodiorite. The major- and trace-element signature of the Spitz Gneiss is similar to some Late Proterozoic granodiorite suites in the Moravo-Silesian Unit (e.g. the Passendorf-Neudegg suite in the Thaya Batholith). However, granodiorites of such type and age do not occur elsewhere in the Moldanubian Zone of the Bohemian Massif. This observation fits existing tectonic models in which the Austrian Drosendorf Unit is considered allochthonous and part of the Moravo-Silesian Unit and the Avalonian Superterrane. Mineral chemistry data for amphibole, plagioclase and biotite allow an estimation of the Variscan peak regional metamorphic conditions for the Spitz Gneiss at ˜700 °C and 7 kbar. Amphibole and plagioclase show hardly any signs of retrograde reequilibration, implying a fast late-Variscan exhumation. Partial chloritization of biotite indicates late fluid activity at T ˜ 250 °C. ]]>
http://www.jgeosci.org/rss.php?ID=jgeosci.271 Original paper http://www.jgeosci.org/rss.php?ID=jgeosci.271