Cumulate causes for the low contents of sulfide-loving elements in the continental crust

Despite the economic importance of chalcophile (sulfide-loving) and siderophile (metal-loving) elements (CSEs), it is unclear how they become enriched or depleted in the continental crust, compared with the oceanic crust. This is due in part to our limited understanding of the partitioning behaviour of the CSEs. Here I compile compositional data for mid-ocean ridge basalts and subduction-related volcanic rocks. I show that the mantle-derived melts that contribute to oceanic and continental crust formation rarely avoid sulfide saturation during cooling in the crust and, on average, subduction-zone magmas fractionate sulfide at the base of the continental crust prior to ascent. Differentiation of mantle-derived melts enriches lower crustal sulfide- and silicate-bearing cumulates in some CSEs compared with the upper crust. This storage predisposes the cumulate-hosted compatible CSEs (such as Cu and Au) to be recycled back into the mantle during subduction and delamination, resulting in their low contents in the bulk continental crust and potentially contributing to the scarcity of ore deposits in the upper continental crust. By contrast, differentiation causes the upper oceanic and continental crust to become enriched in incompatible CSEs (such as W) compared with the lower oceanic and continental crust. Consequently, incompatible CSEs are predisposed to become enriched in subduction-zone magmas that contribute to continental crust formation and are less susceptible to removal from the continental crust via delamination compared with the compatible CSEs

Chemistry and Sr–Nd isotope signature of amphiboles of the magnesio-hastingsite-pargasite-kaersutite series in Cenozoic volcanic rocks: Insight into lithospheric mantle beneath the Bohemian Massif

Amphibole phenocrysts and xenocrysts from Cenozoic volcanic rocks of the Bohemian Massif (BM) belong to the magnesio-hastingsite-pargasite-kaersutite series. Their host rocks are mostly basaltic lavas, dykes and breccia pipe fills, less commonly also felsic rocks from rift zones along lithospheric block boundaries of the BM. The calculated p–T conditions suggest that almost all amphiboles crystallized in a relatively narrow temperature range (1020–1100 °C) at depths of 20–45 km (0.7–1.2 GPa) during the magma ascent. The initial 143Nd/144Nd and 87Sr/86Sr ratios of amphiboles (0.51266–0.51281 and 0.70328–0.70407, respectively) are similar to those of their whole rocks (0.51266–0.51288 and 0.70341–0.70462, respectively). This testifies to locally elevated proportions of recycled Variscan crustal material during melting of mantle peridotites rich in clinopyroxene–amphibole veins. These veins were formed by metasomatic fluids enriched in High Field Strength Elements and are isotopically similar to EM-1 mantle type.Fenokrysty a xenokrysty amfibolů kenozoických vulkanických hornin Českého masivu (ČM) náleží svým složením do magnesiohastingsit-pargasit-kaersutitové série. Jejich hostitelské horniny jsou především bazaltické lávy, žíly nebo brekciovité výplně komínů, méně často také felsické horniny z riftových zón podél hranic litosférických bloků ČM. Vypočtené p-T podmínky ukazují, že téměř všechny amfiboly krystalizovaly v relativně úzkém teplotním rozmezí (1020–1100 °C) v hloubkách 20–45 km (0,7–1,2 GPa) během výstupu magmatu. Iniciální izotopové poměry 143Nd/144Nd a 87Sr/86Sr v amfibolech jsou v rozmezí 0,51266–0,51281 a 0,70328–0,70407. To vypovídá o lokálně zvýšeném množství recyklovaného variského korového materiálu během tavení plášťového peridotitu bohatého na klinopyroxen-amfibolové žíly. Tyto žíly vznikly z metasomatických fluid obohacených o prvky s velkým iontovým potenciálem a jsou izotopově podobné obohacenému plášti typu 1 (EM-1)

Recommendations of RILEM TC 260-RSC for using superabsorbent polymers (SAP) for improving freeze–thaw resistance of cement-based materials

This recommendation is focused on application of superabsorbent polymers (SAP) for the improvement of the resistance of cement-based materials to freeze—thaw attack with or without deicing salts. A simple approach to the determination of the amount and properties of SAP as well as methods to verify SAP effectiveness for frost resistance protection are presented

Hf–Zr anomalies in clinopyroxene from mantle xenoliths from France and Poland: implications for Lu–Hf dating of spinel peridotite lithospheric mantle

Clinopyroxenes in some fresh anhydrous spinel peridotite mantle xenoliths from the northern Massif Central (France) and Lower Silesia (Poland), analysed for a range of incompatible trace elements by laser ablation inductively coupled plasma mass spectrometry, show unusually strong negative anomalies in Hf and Zr relative to adjacent elements Sm and Nd, on primitive mantle-normalised diagrams. Similar Zr–Hf anomalies have only rarely been reported from clinopyroxene in spinel peridotite mantle xenoliths worldwide, and most are not as strong as the examples reported here. Low Hf contents give rise to a wide range of Lu/Hf ratios, which over geological time would result in highly radiogenic εHf values, decoupling them from εNd ratios. The high 176Lu/177Hf could in theory produce an isochronous relationship with 176Hf/177Hf over time; an errorchron is shown by clinopyroxene from mantle xenoliths from the northern Massif Central. However, in a review of the literature, we show that most mantle spinel peridotites do not show such high Lu/Hf ratios in their constituent clinopyroxenes, because they lack the distinctive Zr–Hf anomaly, and this limits the usefulness of the application of the Lu–Hf system of dating to garnet-free mantle rocks. Nevertheless, some mantle xenoliths from Poland or the Czech Republic may be amenable to Hf-isotope dating in the future

Lead isotope evolution of the Central European upper mantle: Constraints from the Bohemian Massif

This study focuses on Pb isotope data and whole-rock geochemistry of intrusive and extrusive volcanic rocks of the Bohemian Massif that sampled the upper mantle. Special attention is paid on whether Late Palaeozoic to Quaternary Central European mantle-derived rocks sampled different mantle sources on a local to regional scale and through time.Tato studie se zabývá Pb izotopovými daty a horninovou geochemií intruzivních i výlevných vulkanických hornin Českého masivu, které vzorkovaly svrchní plášť. Speciální důraz je kladen na to, zda pozdně paleozoické až kvartérní středoevropské horniny odvozené z pláště vzorkují odlišné plášťové zdroje v lokálním až regionálním měřítku a v průběhu času

Highly refractory Archaean peridotite cumulates: Petrology and geochemistry of the Seqi Ultramafic Complex, SW Greenland

This paper investigates the petrogenesis of the Seqi Ultramafic Complex, which covers a total area of approximately 0.5 km2. The ultramafic rocks are hosted by tonalitic orthogneiss of the ca. 3000 Ma Akia terrane with crosscutting granitoid sheets providing an absolute minimum age of 2978 ± 8 Ma for the Seqi Ultramafic Complex. The Seqi rocks represent a broad range of olivine-dominated plutonic rocks with varying modal amounts of chromite, orthopyroxene and amphibole, i.e. various types of dunite (s.s.), peridotite (s.l.), as well as chromitite. The Seqi Ultramafic Complex is characterised primarily by refractory dunite, with highly forsteritic olivine with core compositions having Mg# ranging from about 91 to 93. The overall high modal contents, as well as the specific compositions, of chromite rule out that these rocks represent a fragment of Earth’s mantle. The occurrence of stratiform chromitite bands in peridotite, thin chromite layers in dunite and poikilitic orthopyroxene in peridotite instead supports the interpretation that the Seqi Ultramafic Complex represents the remnant of a fragmented layered complex or a magma conduit, which was subsequently broken up and entrained during the formation of the regional continental crust. Integrating all of the characteristics of the Seqi Ultramafic Complex points to formation of these highly refractory peridotites from an extremely magnesian (Mg# ~ 80), near-anhydrous magma, as olivine-dominated cumulates with high modal contents of chromite. It is noted that the Seqi cumulates were derived from a mantle source by extreme degrees of partial melting (>40%). This mantle source could potentially represent the precursor for the sub-continental lithospheric mantle (SCLM) in this region, which has previously been shown to be ultra-depleted. The Seqi Ultramafic Complex, as well as similar peridotite bodies in the Fiskefjord region, may thus constitute the earliest cumulates that formed during the large-scale melting event(s), which resulted in the ultra depleted cratonic keel under the North Atlantic Craton. Hence, a better understanding of such Archaean ultramafic complexes may provide constraints on the geodynamic setting of Earth’s first continents and the corresponding SCLM.Department of Geological Sciences, Stanford University, 450 Serra Mall, Stanford, CA 94305, USA Department of Earth & Planetary Sciences, McGill University, Quebec, Canada Department of Geology, Lund University, Sölvegatan 12, 223 62 Lund, Sweden School of Earth and Ocean Sciences, Cardiff University, Main Building, Cardiff CF10 3AT, United Kingdom College of Science, University of Derby, Derby, DE22 1GB, U

Konzeption einer modular aufgebauten, cross-medialen Veranstaltungsreihe zur Förderung der textuellen Kohärenzbildung und Lesemotivation von Grundschülern der 4. Klasse innerhalb einer Bildungspartnerschaft zwischen Schule und Bibliothek in öffentlichen Bibliotheken

In der vorliegenden Arbeit wird ein modular aufgebautes, cross-mediales Konzept zur Förderung der textuellen Kohärenz und Lesemotivation von Grundschüler*innen der 4. Klasse innerhalb einer Bildungspartnerschaft in öffentlichen Bibliotheken entwickelt. Sie fußt auf wissenschaftlichen Erkenntnissen zur Lesekompetenz, der Spezifik digitalen Lesens sowie deren Förderung und der Darstellung des schulischen Kontexts, der Initiative Bildungspartner NRW und bibliothekarischer Leseförderung. Die Veranstaltungsreihe besteht aus 3 Formaten, in denen diese Erkenntnisse aufgegriffen und auf die entwickelten Inhalte angewendet werden. Sie werden systematisch anhand der Aspekte der Förderung der textuellen Kohärenz und der Lesemotivation aufeinander aufgebaut und miteinander verknüpft. Dem cross-medialen Aspekt wird durch das Verwenden digitaler Medien und ein Format zur Förderung des digitalen Lesens Rechnung getragen. Die Arbeit zeigt auf, dass sich die Förderung der textuellen Kohärenzbildung mit der Förderung der Lesemotivation sinnvoll verbinden lässt und diese Aspekte nicht isoliert voneinander betrachtet und gefördert werden müssen.This bachelor thesis develops a set of modular, cross-medial event-concepts for the promotion of establishing text coherence and reading motivation in public libraries and is developed as a collaboration between primary schools and public libraries. The target groups are primary school students in the age range of 9-11. The event-concepts are developed upon scientific findings regarding reading comprehension, digital reading, their promotion and a presentation of the initiative Bildungspartner NRW, the scholastic context and reading promotion in public libraries. The set of event-formats consists of 3 concepts, in which those findings are taken up and elaborated in coordination with the newly developed content. Digital media is the focus of the cross-medial aspect in this thesis and a systematic part of all 3 concepts. The thesis shows the possibility of combining concepts for the promotion of establishing textual coherence and reading motivation usefully