Iceland is one of the few places on earth where it is possible to see an active spreading ridge above the sea level with the two plates moving apart. This country lies in fact over both a plume hot material, up-welling from great depths, and the Mid-Atlantic Ridge, at the boundary between the North American and Eurasian tectonic plates where new oceanic crust is being created. The continued volcanic activity associated to this geologically complex area has produced a lot of high-temperature geothermal systems. Inside these geothermal fields, the hydrothermal alteration of basaltic rocks is very effective. In the frame of the international Iceland Deep Drilling Project (IDDP) we have carried out in-situ (EMP+SIMS) analyses on both magmatic (plagioclase and clinopyroxene) and hydrothermal (amphibole and epidote) phases in 11 drill-cutting samples, selected on the basis of different depths (400-3000 m) from the well RN-17, which is from within the Reykjanes geothermal fields in SW Iceland. The present study has been focused on determining the concentrations of some of so-called hydrothermal markers, such as the light lithophile (Li, B) and halogen (Cl) elements that were investigated by SIMS with a Cameca IMS 4f ion microprobe installed at CNR-IGG (Pavia). In addition, the Sr isotope ratio (87Sr/86Sr), determined at CNR-IGG (Pisa) by Thermal Ionization Mass Spectrometry (TIMS) with a Finnigan Mat 262 was utilized as a further hydrothermal marker. The selected samples were shown to be affected by a significant compositional inhomogeneity of the mineral assemblage at a few-micron scale (both laterally and in-depth). Nevertheless, the application of sensitive, high-resolution techniques, such as those used here, has allowed us to face the study of the geochemical composition (major, minor and trace constituents) in complex, altered matrixes, and arrive at conclusions on the hydrothermal alteration degree in a region which is of great scientific and economic interest.
The application of micro-analytical techniques to complex matrixes: the case study of altered basalts from Reykjanes geothermal field (SouthWest Iceland)
OTTOLINI L;TONARINI S;GIANELLI G;
2007
Abstract
Iceland is one of the few places on earth where it is possible to see an active spreading ridge above the sea level with the two plates moving apart. This country lies in fact over both a plume hot material, up-welling from great depths, and the Mid-Atlantic Ridge, at the boundary between the North American and Eurasian tectonic plates where new oceanic crust is being created. The continued volcanic activity associated to this geologically complex area has produced a lot of high-temperature geothermal systems. Inside these geothermal fields, the hydrothermal alteration of basaltic rocks is very effective. In the frame of the international Iceland Deep Drilling Project (IDDP) we have carried out in-situ (EMP+SIMS) analyses on both magmatic (plagioclase and clinopyroxene) and hydrothermal (amphibole and epidote) phases in 11 drill-cutting samples, selected on the basis of different depths (400-3000 m) from the well RN-17, which is from within the Reykjanes geothermal fields in SW Iceland. The present study has been focused on determining the concentrations of some of so-called hydrothermal markers, such as the light lithophile (Li, B) and halogen (Cl) elements that were investigated by SIMS with a Cameca IMS 4f ion microprobe installed at CNR-IGG (Pavia). In addition, the Sr isotope ratio (87Sr/86Sr), determined at CNR-IGG (Pisa) by Thermal Ionization Mass Spectrometry (TIMS) with a Finnigan Mat 262 was utilized as a further hydrothermal marker. The selected samples were shown to be affected by a significant compositional inhomogeneity of the mineral assemblage at a few-micron scale (both laterally and in-depth). Nevertheless, the application of sensitive, high-resolution techniques, such as those used here, has allowed us to face the study of the geochemical composition (major, minor and trace constituents) in complex, altered matrixes, and arrive at conclusions on the hydrothermal alteration degree in a region which is of great scientific and economic interest.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
