Combined in situ XRF–LIBS analyses as a novel method to determine the provenance of central Mediterranean obsidians

This work presents a new calibration method for determining the provenance of obsidian artefacts based on the combined use of XRF and laser-induced breakdown spectroscopy (LIBS). At first, obsidian samples collected from the main Mediterranean sources were characterized using portable XRF and LIBS systems. After data treatment, elemental information was used to carry out principal component analysis (PCA) for each technique. Rb, Sr, Zr, Y and Fe elements, detected by using XRF, were found to be the key parameters enabling obsidians discrimination. Likewise, LIBS data helped differentiating the analysed patterns by the intensity of their main elemental components (Ca, Al, Mg and K). After selecting the key parameters detected by each technique, a new data matrix combining XRF and LIBS data was finally built. According to PCA results, the discrimination of Mediterranean sources based on combined XRF–LIBS data ensured a higher reliability over mono-analytical models, by increasing the Euclidean distance between sources projections over three-dimensional principal components plots. Knowing that the representativeness of elemental data could be compromised by the presence of superficial degradation products or deposition patinas, a shot-to-shot comparison of in-depth LIBS analyses is finally proposed as a method to disclose whether the spot under analysis was superficially contaminated or altered. Thus, the proposed strategy based on the combined use of portable XRF and LIBS spectrometers could be particularly useful for the in situ analysis of obsidian artefacts that underwent superficial alteration or could be covered by patina products.This work has been financially supported by the DEMORA project (Grant No. PID2020-113391GB-I00), funded by the Spanish Agency for Research (through the Spanish Ministry of Science and Innovation (Grant No. BIA2017-870´63-P), MICINN, and the European Regional Development Fund (Grant No. BIA2017-870´63-P), FEDER). I. Costantini gratefully acknowledges to the UPV/EHU for her postdoctoral contract. Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature

Use of Temperature Controlled Stage Confocal Raman Microscopy to Study Phase Transition of Lead Dioxide (Plattnerite)

The present work concerns the study of the phase transition of plattnerite [β-PbO2 lead (IV) oxide]-based samples when they are analysed by Raman spectroscopy. The laser-induced degradation process was carried out either on historical painting samples, where plattnerite was present as a degradation product of lead-based pigments, or commercial plattnerite samples as powder and pellets. The Raman spectra of plattnerite taken at low excitation power, to avoid phase transformations, are reported up to low wavenumbers, and they were characterized by the features at 159, 380, 515 and 653 cm−1 and a shoulder at 540 cm−1. The degradation of plattnerite was induced by increasing the laser power on the sample, and the formation of its secondary products red lead (Pb3O4), litharge (α-PbO) and massicot (β-PbO), when varying the laser power, is discussed. The analyses were performed in a controlled condition by coupling the Raman spectrometer to a temperature-controlled stage (Linkam THMS600- Renishaw), which allows for varying the sample temperature (from room temperature up to 600 °C) and keeping it constant inside the stage during the analysis. In this way, commercial plattnerite samples were heated by increasing the cell temperature to verify the temperature range at which the phase transitions of lead dioxide occur. In addition, thanks to the construction of temperature ramps, all the degradation pathways were shown, and other lead compounds were identified, generated by the laser power contribution. A different behaviour was found between pigments from historical painting samples and commercial samples under the effect of the laser. This information could be useful in order to recognize their nature when they are found in cultural heritage materials.This research was funded by the Spanish Agency for Research AEI (MINEICO/FEDER-UE), grant number BIA2017-87063-P

Bizkaiko itsaspeko sumendiaren analisi geokimikoa

Evidence of geomorphology traces of past liquid water on the surface of Mars suggests that this planet once had habitable conditions and leads to question about life. To investigate that, ESA and NASA space explorations organizations will send two rovers. For this reason, the necessity for the proper understanding and interpretation of the results obtained implies the study of terrestrial Martian analogues. In this work, Armintza, the Cretaceous alkaline submarine volcano outcrop has been studied and proposed as a Martian analogue. The samples were geochemically characterizes by Raman and Vis-NIR spectroscopies, considering that they are the two techniques that will go on-board the rovers of the next planetary missions. As was expected, silicates (phyllosilicates) were the major minerals but also compounds such as carbonates, sulphates and oxides could be detected. Phyllosilicates have special importance because they are indicators of aqueous weathering processes of primary magmatic rocks and they need liquid water for their formation. In addition, these compounds have been reported to be present in the Mars surface, specifically in Oxia Planum, the landing site for the Exomars2020 rover of the ESA mission as well as in Jezero crater, the landing site for the Mars 2020 rover of the NASA mission.; Marteko iraganeko lurzoruan agerian utzitako ur-likidoaren aztarna geomorfologikoak noizbait izandako bizigarritasun-baldintzetara aditzera ematen du eta honek, bizitzari buruzko galderak egitera. Horretarako 2020. urtean ESA-k eta NASA-k Martera ibilgailu robotiko bana bidaliko dute. Beraz, lortutako emaitzak ulertzeko eta interpretatzeko lurreko analogoen ikerketak egitea garrantzitsua da. Ikerketa lan honetan, Armintza, Kretazeo garaian gertatutako izaera alkalinodun itsaspeko sumendiaren ondoriozko azaleratzea Marteko analogo gisa proposatu da. Laginen ikerketa geokimikoa egiteko hurrengo Marteko misioetan erabiliko diren Raman eta Vis-NIR espektroskopia teknikak erabili dira. Espero zen bezala konposatu nagusienak silikatoak (filosilikatoak) dira, hala ere, karbonatoak, sulfatoak eta oxidoak ere karakterizatu dira. Filosilikatoek garrantzi handia dute lehen mailako arroka magmatikoen meteorizazio prozesuen adierazleak direlako eta ura beharrezkoa dutelako haien eraketetarako. Gainera, filosilikatoak Marten aurkitu dira, bereziki Oxia Planumen, ESA-ren Marteko ExoMars 2020 misioaren lurreratze tokia baita Jezero kraterrean ere, NASA-ren Mars 2020 misioaren lurreratze tokia

Study of a Terrestial Martian Analogue: Geochemical Characterization of the Meñakoz Outcrops (Biscay, Spain)

Collection of the raw Raman and NIR spectral dat

Study of a Terrestial Martian Analogue: Geochemical Characterization of the Meñakoz Outcrops (Biscay, Spain)

Collection of the raw Raman and NIR spectral dat