PIXE and EMP analyses of volcanites from Nea Kameni (Aegean Sea, Greece).

The major and trace element compositions of several minerals and their surrounding groundmass in the volcanic rocks from the post-caldera Nea-Kameni island of the Santorini volcanic complex, Aegean Sea, have been determined, in-situ with particle-induced X-ray emission (PIXE) and wavelength dispersive X-ray analysis with an electron microprobe (EMP). The lavas are typically calc-alkaline dacites. All samples are porphyritic with a phenocryst mineralogy dominated by plagioclase, augite, hyperstene and Ti-magnetite. The phenocrysts range in size from 200/~m to 2.5 mm. The PIXE and EMP analyses were done on sections polished with diamond paste. They were sufficiently thick (~ 100/~m) to stop the 2.7 MeV protons used for the analysis and yet thin enough for individual minerals to be seen with transmitted light. The specific minerals and groundmass areas to be analyzed had been selected and marked through conventional microscopic examination prior to analysis. Solid/liquid partition coefficients, which depend much less significantly on the method for determining the concentrations were calculated from the element abundances in phenocrysts and corresponding groundmass.