Search

[Display omitted] • Evaluation of activating solution influence on high temperature resistance in AAMs. • Higher availability of silicon and aluminum and better feasibility of the pastes. • Monitoring formation of Si-O-Si and Si-O-Ca networks. • Positive influence of the new crystallizations on mechanical resistance after 1000 °C. • Densification behavior of K sample contrary to the melting of that Na. Thermal performances at 1000 °C of volcanic ash-based alkali-activated materials by both sodium or potassium solutions have been tested. Once defined the feasibility for the potassium set, a multidisciplinary characterization including spectroscopic, thermal, mechanical, diffractometric before and after treatment and dilatometric analyses was applied. The formation kinetics of different networks was evaluated. A correlation between the high mechanical properties and the least amount of water was observed in non-treated samples. Treated samples at 1000 °C showed higher compressive strengths due to the crystallization of wollastonite, leucite and nepheline. Thermal stability was observed increased with the solid content in the potassium-based formulations. [ABSTRACT FROM AUTHOR]

The results of a petrographic and geochemical study carried out on archeological grindstones allow to provide new constraints on protohistoric commercial exchanges over the Mediterranean area. Eleven grindstones, discovered in an archeological site located in Milazzo (Messina, Sicily) and dated from the Early Bronze Age, have been investigated by geochemical and petrographic techniques. The raw materials are mainly volcanic rocks characterized by calc-alkaline and K-alkaline affinities with volcanic arc geochemical signature. Only one sample, made of basalt belonging to the Na-alkaline series, shows an intraplate signature. The comparison with the available literature data for similar rocks allowed constraining the volcanic origin of the exploited lavas. While the intraplate-type raw material came from Mt. Etna Volcano (Sicily), the arc-type volcanic rocks are mostly trachyandesites, basaltic andesites, and one rhyolite. Although most of them come from the Aeolian Arc, a provenance of some samples from the Aegean Arc cannot be excluded. This last region could represent the most probable provenance area for the rhyolite sample. [ABSTRACT FROM AUTHOR]

Abstract: We address general features of carbonatite monogenetic volcanic fields located in continental settings which are peculiar being associated with kamafugites or melilite-bearing leucitites. Instructive examples are the Toro Ankole in Uganda, West Qinling in China, and Campo de Calatrava in Spain and the Intra-mountain Ultra-alkaline Province (IUP) of Italy. Maars are the typical volcanic forms, occurring in isolation or in clusters along fault systems. Concentric-shelled juvenile lapilli and bombs, having a upper-mantle peridotite kernel, are unique to this type of volcanism. These pyroclasts are interpreted as the result of deep-seated fragmentation of magma having a high carbon dioxide-water (CO2/H2O) ratio. The presence of discrete, large peridotitic nodules implies a high-velocity propagation of magma, while the associated large CO2 emission suggests a high proportion of juvenile CO2. Magma fragmentation is inferred to occur as a consequence of explosive CO2 exsolution at the upper mantle level (diatresis) followed by immiscibility. Based on field evidence, carbonatitic maar formation could be due to violent CO2 expansion and does not require phreatomagmatic phenomena. Extrusive carbonatites and associated rocks represent very primitive melts having a distinct High Field Strength Elements (HFSE) distribution, the source of which is related to enriched mantle. Carbonated peridotite is a stable paragenesis at depths of 400–600 km; thus, primary carbonatitic silicate magma can be produced at these depths as a consequence of rising deeper melt/fluids that are trapped at the transition zone. In our opinion, carbonatitic carbon is linked to the primary process of deep-mantle differentiation and Earth''s core degassing. [Copyright &y& Elsevier]

Laser-induced breakdown spectroscopy (LIBS) is an important analytical technique in a variety of fields ranging from in-situ terrestrial geological field investigations to robotic exploration missions of extraterrestrial bodies such as Mars. In this study, the performance of a commercial handheld LIBS instrument was evaluated during an international summer school in 2019 that focused on the exploration of extreme environments on Earth and in space. Several sites on the Eolian island Vulcano (Italy) were investigated with different spectroscopic methods including LIBS. We focus here on the exploration of one particular outcrop with LIBS, where layered and colored ash deposits were observed. Furthermore, a laboratory study was performed to investigate and validate the effect of varying distance of the instrument to the sample. Unsupervised principal component analysis (PCA) for data exploration showed that elemental variations between the layers of the outcrop can be observed with the LIBS data from the handheld instrument. This was further confirmed by a layer-by-layer analysis of elemental correlations and depositional trends. Geologically relevant major elements such as Si, Al, Ca, Fe, K, Mg, and Na could be identified but also minor and trace elements such as F, Li, Mn, and Sr. Our results also show that the effects of varying distances of the instrument to the sample are critical for the quality of the data acquired and hence pose significant challenges to the analysis and interpretation. We propose a dedicated data pre-processing approach, which includes the masking of emission lines of Ar from the locally induced Ar atmosphere, as a possible solution to overcome this challenge. Overall, this study provides a better understanding of the performance and limitations of a handheld LIBS instrument, particularly in the context of future terrestrial and planetary field investigations. Unlabelled Image • Field investigation of volcanic ash layer deposits with handheld LIBS instrumentation • Analysis of samples in their original context • Demonstration of LIBS capability to reveal elemental variations among the layers • Evaluation and discussion of the performance of the handheld LIBS device for geological field investigations [ABSTRACT FROM AUTHOR]