Georgios Christofides

Forty-nine samples from several plutons in northern Greece have been studied for their activity concentrations of 40K, 226Ra and 232Th by using gamma-ray spectroscopy. The activities of 40K, 226Ra and 232Th of the majority of the samples exceed the average level of these radionuclides in soil and building materials. Samples of basic composition have very low concentrations of radionuclides while intermediate and acid rocks are more enriched in 40K, 226Ra and 232Th and their decay products. In order to assess the radiological impact from the investigated rocks, absorbed gamma dose rate (Da), annual effective dose (HE), activity index (AI) and gamma-ray index (Iγ) were estimated. The activity concentrations and hazard indices were compared to those of plutonic rock samples from all over the world, as well as other building materials. The average of hazard indices of Greek granites is below ‘world’ average in all cases. Moreover, it is still bellow the criteria of UNSCEAR (2000). Therefore, at least from radiological point of view and for the investigated rocks, the use of granites from northern Greece as building materials is recommended.

Emplacement of the Xanthi Plutonic Complex within the Rhodope Massif of N. Greece created an extensive metamorphic aureole around the plutonite. The aureole contains two areas of intense scapolitization in the contacts between granodiorite and biotitegneiss and between monzonite and sandstone, the latter cross-cut by andesite dykes. This paper reports the results of a mineralogical and geochemical study into the formation of the scapolites and particularly the nature of the plutonite-derived hydrothermal fluids from which scapolites were formed.

Tertiary plutonic and volcanic rocks cropping out in the Rhodope Massif (N. Greece) are studied using existing and new geochemical and isotopic data. Most of these rocks belong to the post-collisional magmatism formed as part of the prolonged extensional tectonics of the Rhodope region in Late Cretaceous– Paleogene time. This magmatism is considered to be of mantle origin; however, the character of the mantle source is controversial. Rock bulk chemistry and compositional variations show magmas with calc-alkaline to high-K calc-alkaline and shoshonitic features associated with magmatism at convergent margins. Initial 87Sr/86Sr, 143Nd/144Nd ratios, Pb isotopes and REE composition of the mafic rocks indicate mainly an enriched mantle source, even if some rocks indicate a depleted mantle source. Low- and High-K mafic members of these rocks coexist indicating a strongly heterogeneous mantle source. The High-K character of some of the mafic rocks is primarily strongly related to mantle enrichment by subduction-related components, rather than crustal contamination. The geochemical characteristics of the studied rocks (e.g Ba/Th,Th/Yb,Ba/La, U/Th, Ce/Pb) indicate that primarily sediments and/or sediment melts, rather than fluid released by the subducted oceanic crust controlled the source enrichment under the Rhodope Massif.

New K/Ar mineral ages of thirty nine samples (biotite, muscovite, K-feldspar) from the two-mica granodiorite to granite and leucogranite of the northern part of the Sithonia Plutonic Complex (Chalkidiki, Greece) are given in the present study. These data along with existing Rb/Sr mica and U/Pb zircon ages are used to investigate the thermal history of the plutonic complex and shed light on the process that affected it, and caused discordant Rb/Sr and K/Ar mineral ages. The K/Ar mineral dating yielded ages ranging from 38 to 49 Ma for muscovites, 32 to 47 Ma for biotites and 37 to 43 Ma for K-feldspars, respectively. The comparison of the K/Ar, Rb/Sr and U/Pb mineral ages and the closure temperatures of the different isotopic systems for the different minerals indicate a rapid cooling rate for the Sithonia pluton. The latter supports the hypothesis that the pluton was formed in a post orogenic extensional regime. Moreover, the K/Ar mineral isochrones indicate that a reheating of the pluton took place before 37 Ma and partially rejuvenated the K/Ar and Rb/Sr isotopic system of the minerals

Powder IR spectra of natural Ca-amphiboles were studied in the spectral range 4000 to 400 cm'1. The examined samples are: actinolite, tremolite, Mg-hornblende and pargasite. According to their spectra all the minerals of the four species present common features at 3658-3660, 919, 683-687, 661-668, 505-513, 457-464 and 419 cm . Additionally to these bands, the spectra of the actinolites, tremolites and Mghornblendes present common characteristics at 3673, 1094-1098, 989-998, 951, 752-758 and 441-449 cm'1. Moreover, six absorption bands are shown in the spectra of the pargasites at 3690, 981-984, 931, 805-811, 734 and 696-698 cm'1, in addition to the common bands appeared in all Ca-amphiboles, which do not appear in the spectra of the actinolites, tremolites and Mg-hornblendes. The spectra of pargasites are remarkably different from the spectra of the other three mineral species. These discrepancies could be attributed to differences in the structure of pargasites relative to the other three species as well as to the occupancy of the A site especially with Na+.