Kirsten Drüppel

Early- to mid-Silurian extrusion wedge tectonics in the central Scandinavian Caledonides

We present evidence for an extrusion wedge in the Scandian fold-thrust belt of the central Scandinavian Caledonides (Seve nappe complex). Rb-Sr multimineral geochronology in synkinematic assemblages indicates simultaneous movements at the normal-sense roof shear zone and at the reverse-sense floor shear zone between 434 Ma and 429 Ma. A Sm-Nd age of 462 Ma from a mylonitic garnet mica schist documents prograde garnet growth and possible incipient subduction. Pressure-temperature pseudosection calculations provide evidence for eclogite facies metamorphic conditions and nearly isothermal decompression at ∼670 ± 50 °C from 17.5 to 14.5 kbar in garnet-kyanite mica schists during reverse-sense shearing, and from 15 to 11 kbar in garnet mica schists during normal-sense shearing. These data and the presence of decompression-related pegmatites dated at 434 Ma and 429 Ma indicate that the Seve nappes form a large-scale extrusion wedge. This wedge extends along strike for at least 150 km and marks an early stage of ultrahigh-pressure metamorphism, exhumation, and orogenic wedge formation in this part of the Scandinavian Caledonides predating the major, post–415 Ma ultrahigh-pressure exhumation processes in southwestern Norway.

Origin and geodynamic evolution of late Cenozoic potassium-rich volcanism in the Isparta area, southwestern Turkey

Post-collisional potassic-rich volcanism of Gölcük Volcano in the Isparta area of southwestern Turkey consists of two groups: (i) extracaldera lavas, corresponding mainly to Pliocene activity; and (ii) intracaldera lavas and pyroclastics (ignimbrite flows and ash/pumice fall deposits) formed during the Quaternary. Extracaldera volcanic rocks mainly comprise lamprophyre (minette), basaltic trachyandesite, trachyandesite, and trachyte. A close relationship exists between the silica content and phenocryst type in the extracaldera volcanics such that trachyte–trachyandesites with SiO2 < 57 wt% and basaltic trachyandesites are characterized mainly by mafic phenocryst phases (e.g. pyroxene, amphibole, biotite–phlogopite). These features suggest suppression of plagioclase crystallization under high H2O pressure conditions. Intracaldera volcanics are composed of tephriphonolitic dikes, remnants of lava flows and domes at the caldera rim, and a trachytic lava dome on the caldera floor. The Gölcük flows and pyroclastics are mainly characterized by strong incompatible element enrichment in large ion lithophile elements (LILEs; e.g. Cs, Ba, U, and Th) relative to K, Rb, and high-field strength elements (e.g. Nb, Ta, and Ti). We conclude that the Gölcük lavas were derived from a metasomatized lithospheric mantle source containing phlogopite–amphibole garnet peridotite; the latter resulted from metasomatism by a hydrous fluid phase related to subducted sediments and oceanic crust. The parental magma for the extracaldera volcanics was lamprophyric, and that for the intracaldera volcanics was basanitic. All the geological and geochemical data show that the alkaline Gölcük lavas display a gradual decrease in silica content with decreasing eruption age, indicating that, in the Isparta volcanic province, the asthenospheric melt component became more important over time. In the extracaldera volcanics, 87Sr/86Sr isotope ratios of the evolved trachyte–trachyandesites range between 0.70366 and 0.70504, whereas these ratios are lower in the less evolved basaltic trachyandesite and lamprophyres, varying in narrow ranges around 0.70365 and between 0.70374 and 0.70453, respectively. The 143Nd/144Nd values lie between 0.51264 and 0.51273 in trachyandesites, 0.51267 and 0.51273 in basaltic trachyandesites, and 0.51270 and 0.51274 in lamprophyres. In the intracaldera lavas, the 87Sr/86Sr isotope ratio is 0.70361 in the tephriphonolite and 0.70388 in the intracaldera trachytic lava dome. The 143Nd/144Nd isotope ratio is 0.51274 in the analysed tephriphonolitic flow and 0.51271 in the intracaldera trachytic lava dome; these values are higher than that of trachyte–trachyandesites of the extracaldera volcanics. The Sr–Pb isotopic signatures indicate that crustal contamination was significant for the evolved extracaldera volcanics, but was negligible for the intracaldera volcanics. The εNd values of the Gölcük volcanics range between 0 and 2.0. The low Sr isotope ratios and positive εNd values are characteristic features of a depleted mantle source. The isotopically depleted and incompatible enriched nature of the Gölcük lavas point to recent enrichment processes prior to partial melting of the mantle source. Conversely, their radiogenic lead isotope compositions (206Pb/204Pb = 19.19–19.54, 207Pb/204Pb = 15.64–15.67, 208Pb/204Pb = 39.12–39.49) indicate an enriched mantle source region.

The system Al2O3-P2O5-H2O at temperatures below 200 °C: Experimental data on the stability of variscite and metavariscite AlPO4·2H2O

Abstract The system Al2O3-P2O5-H2O contains many phosphate minerals that occur in various geologic environments. The natural occurrence of variscite (AlPO4·2H2O, orthorhombic), including its monoclinic polymorph metavariscite, is largely restricted to soils and aluminous rocks like Al-rich igneous rocks and shales, which interacted with P-rich hydrothermal solutions or groundwater. Variscite dehydrates to berlinite (AlPO4) and a hydrous P-Al-rich fluid. This dehydration reaction AlPO4·2H2O = AlPO4 + 2H2O is, however, metastable, at low concentrations of P in the fluid, because berlinite breaks down at lower temperature to augelite [Al4PO4(OH)3] + H3PO4 + H2O and trolleite [Al4(PO4)3(OH)3] + H3PO4 + H2O. The variscite/metavariscite = berlinite equilibrium has been investigated by synthesis experiments from mixtures of γ-Al2O3 and excess phosphoric acid at pressures between 1 and 5 kbar and temperatures of 100-200 °C using standard cold-seal vessels. The hydration-dehydration equilibrium is mainly controlled by temperature and only weakly by pressure. At 4 and 5 kbar, variscite/metavariscite were found at temperatures of ~150 °C, at lower pressure at 115-125 °C in accordance with their natural mode of occurrence. In this T range, however, variscite/metavariscite is not the sole phase but is always accompanied by variable but generally minor amounts of wavellite and trolleite Al4(PO4)3(OH)3. Secondary wavellite Al3(PO4)2(OH)3·5H2O, hydrated Al-phosphate AlPO4·xH2O (1.1 ≤ x ≤ 1.3) and Al-metaphosphate hexahydrate Al(H2PO4)3 formed during quenching and/or drying of the runs. Berlinite is the reaction product at temperatures 200 °C/4-5 kbar and 150 °C/1-3 kbar and may be associated with augelite and trolleite.

Fire bombing of the Tell Halaf Museum in Berlin during World War II -reconstruction of the succession of events based on mineralogical investigations

Basaltic monuments from the Aramaic Tell Halaf (built ca. 1000 BC), Syria were severely damaged during fire bombing of the Tell Halaf Museum, Berlin in World War II. While the museum burst into flames part of the statues were covered with burnt bitumen from the roof of the museum, mixed with fragmented quartz of the roofing cardboard, grinded basalt, limestone artwork, and gypsum casts. Detailed mineralogical investigations of the thin carbon coating on the statues revealed that additionally a number of unexpected, non-basaltic minerals formed in the bitumen via temperature-dependent reactions due to the thermal impact by the bomb blasting and subsequent reequilibration during burning of the exhibition hall. The source material of these newly formed phases was provided by the basalt, the gypsum casts, the limestone artwork, the museum roof, the museum pipe system and, last but not least, the incendiary bomb itself. Phases include sphalerite (zinc of the pipe system + sulphur of gypsum casts), smithsonite (zinc of the pipe system + calcite of limestone artwork), wollastonite (calcium of the limestone orthostats + silica of the roofing cardboard), pyrite (iron of the basalt Fe-oxides + sulphur of the gypsum casts), alkali feldspar (saltpetre of the incendiary bomb + basalt plagioclase), and apatite (phosphorus of the incendiary bomb + calcium of the limestone). A conspicuous feature of samples close to the impact is the abundance of silicate glasses. Observed mineral-forming reactions suggest initial temperature conditions of > 980 °C near the fire centre and of 850–980 °C throughout the museum. The cold water used for fire fighting finally resulted in crack-producing stress that caused severe shelled fracturing of the statues.

Correction to: Flow-through experiments on the interaction of sandstone with Ba-rich fluids at geothermal conditions

After publication of the article (Orywall et al. 2017), it has been brought to our attention that there are a number of errors. The authors have listed them below.