Chemical and mineralogical analysis of a basaltic lava from Reykjanes Peninsula: a comparative multi-analytical approach

The present research reports the study of Reykjanes Peninsula (SW Iceland) basalt, through a multi-analytical investigation. Therefore, Instrumental Neutron Activation Analysis, Electron Microprobe Analysis, X-Ray Fluorescence, Inductively-Coupled Plasma-Mass Spectrometry, X-Ray Diffraction, X-Ray Computed Tomography, and Magnetic Analysis were concurrently used to investigate samples from Reykjanes Peninsula. Bulk rock composition and elemental maps (through Wavelength and Energy-Dispersive Spectrometry techniques) revealed several discrepancies among results, while ternary and trace elements diagrams were used for the assessment of the tectonic setting based on current results and literature data. Mineralogical analysis evidenced abundant plagioclase, pyroxene, as well as Fe-Ti oxides, while olivine and spinel were less present. Similar results have been provided by the Back Scattering Electron images, coupled with the Wavelength-Dispersive Spectrometry, the results being in agreement with the chemical analyses. X-ray computed tomography revealed the presence of a multitude of elongated vesicles indicating a preferential lava flow. This particular feature suggests the existence of an important amount of volatiles which lowered lava viscosity. Raman Spectroscopy was used to confirm the mineral components, and the recorded spectra were compared to the literature on the subject and the RRUFFTM mineralogical database. The FORC diagrams, alongside magnetic susceptibility against temperature and the magnetic field intensities, have shown the presence of titanomagnetite as the main magnetic phase. All the results indicate that the investigated samples have a complex mineralogy, while major and trace elements emphasize the discrepancies between the use of different analytical methods. Moreover, a tholeiitic, oceanic ridge, and “continental” affinities are emphasized by the use of diagrams, while enrichments in several elements are observed with respect to normalized values.