| Popis: |
To get more data concerning de geochemistry and volcanology of Reykjanes Peninsula (Iceland) lavas, more high-precision analytical methods such as Instrumental Neutron Activation Analysis (INAA), Electron Microprobe Analysis (EMPA), X-ray Fluorescence (XRF), X-ray Diffraction (XRD), ICP-MS, X-ray microtomography (XRMT) and magnetism, coupled with mineralogical investigations were used. INAA, EPMA, XRF and ICP-MS were used to determine both major and trace element mass fractions. In the case of major elements, despite some differences inherent utilization of different analytical techniques, all analysis suggested a tholeiitic composition. Several discriminating diagrams clearly emphasize the subalkaline and tholeiitic trend, while the tectonic discrimination diagram assigned a “continental affinity”, as well as the existence of a minor crustal contamination. At their turn, the distribution of incompatible trace elements, represented into several discriminating diagrams, in agreement with PetDB database on Reykjanes Peninsula, as well as Hawaii and St Helen volcanic rocks, confirming the previous hypothesis based on major elements distribution on the tholeiitic and evolved character of the Reykjanes Peninsula lava, with an affinity towards ocean island basalts with traces crustal contamination. The results of mineralogical as well as BSE images analysis evidenced an abundance of plagioclase (albite), pyroxene (augite and pigeonite), as well as Fe-Ti oxides, while minerals such as olivine and spinel were less present. XRMT images revealed the presence of a multitude of vesicles showing preferred orientations, most probable due to lava flow, as the XRMT images loaded into stacks and analyzed by appropriate image analyzing software suggested. This particular features could suggest the existence of an important amount of volatiles, which lowering lava viscosity make them visible among larger vesicles. Raman spectroscopy results concerning the phases of each mineral, compared with literature and RRUFFTM database confirmed previuous finding concerning the geochemistry of investigated Reykjaned Peninsula basalt sample. A magnetic analysis, performed by means of FORC diagrams as well as magnetic susceptibility dependence on temperature and the magnetic field, evidenced the presence of titanomagnetite as a main magnetic present in the sample.Therefore, all analyses suggested that the investigated basaltic lava present a tholeiitic composition, with an evolved continental affinity, but not related to rifting. The structural features suggests the presence of an important amount of volatiles existed prior the eruption. |
