Georgios Christofides

Geochemistry and evolution of the fanos granite, N. Greece

SummaryThe Fanos granite, a Jurassic pluton composed of high silica fine- to coarse-grained leucogranites, is associated with and intrudes the Mesozoic Guevgueli ophiolitic complex. Discriminant diagrams indicate a collision related plate tectonic environment for the rocks studied. They are peraluminous with calc-alkaline affinities. Major and trace element behaviour suggest a fractional crystallization process for the evolution of the Fanos granite. Petrographic calculations, based on major elements, require 32% crystal accumulation mainly of plagioclase, K-feldspar and biotite for a direct model, while for a two-step model 21% and 14% crystal cumulate is required for the first and the second step respectively.ZusammenfassungDer jurassische Fanos-Granit ist ein fein- bis grobkörniger Leukogranit mit hohem Silikatanteil. Er ist mit dem mesozoischen Ophiolithkomplex von Guevgueli, mit dem er in instrusivem Kontakt steht, verknüpft.Diskriminierungsdiagramme weisen darauf hin, dab die untersuchten Gesteine im Zuge kollisions-tektonischer Prozesse gebildet wurden. Die untersuchten peraluminösen Gesteine folgen einem kalkalkalischen Trend. Die Haupt- und Spurenelementverteilungen belegen eine fraktionierte Kristallisation des Fanos-Granites. Einfache Mischungsmodell-Berechnungen, die mittels der Hauptelemente erstellt wurden, ergeben eine 32 %ige Kristallakkumulation von vorwiegend Plagioklas, Kalifeldspat und Biotit. Eine Zweistufenmodell-Berechnung ergab eine 21- beziehungsweise 14 %ige Kristallakkumulation für die erste und zweite Stufe.

Natural radioactivity distribution and gamma radiation exposure of beach sands from Sithonia Peninsula

This study aims to evaluate the activity concentrations of 238U, 226Ra, 232Th, 228Th and 40K along the beaches of Sithonia Peninsula which are adjacent to the rock-types of the Sithonia Plutonic Complex. These range from 6–673, 5–767, 5–1750, 6–1760 and 185–875 Bq/kg respectively. The (% wt.) heavy magnetic (HM) fraction (epidote, allanite, hornblende, biotite and garnet), the heavy non-magnetic (HNM) fraction (monazite, zircon, titanite and apatite) and the total heavy (TH) fraction, were correlated with the concentrations of the measured radionuclides in the bulk samples. The HNM fraction seems to control the activity concentrations of 238U in all samples, while the HM fraction, at least for the heavy mineral rich samples bearing high amounts of epidote crystals with allanite cores, controls their 232Th content. The measured radionuclides in beach sands were normalized to the respective values measured in the granitic rocks, which are their most probable parent rocks, in order to provide data on their enrichment or depletion. The annual effective dose varies from 0.013 to 0.688 mSv y−1 for local people working on the beach, while for tourists the annual external effective dose ranges between 0.003 and 0.165 mSv y−1.

Radioactive secular equilibrium in 238U and 232Th series in granitoids from Greece

Granitoid rocks belonging to plutons of Greece, covering a wide range of compositions and rock-types, have been studied for their specific activity (Bq/kg) of (238)U and (226)Ra from (238)U radioactive series and (228)Ra and (228)Th from (232)Th radioactive series by using gamma-ray spectroscopy. Results on the radioactive secular equilibrium of both (238)U and (232)Th radioactive series are presented by studying the (226)Ra/(238)U and (228)Ra/(228)Th ratios. The majority of the samples are in radioactive secular equilibrium for (226)Ra/(238)U ± 1σ. However, several samples exhibit (226)Ra/(238)U ratios significantly different from 1. The distortion of the secular equilibrium in the (226)Ra-(238)U isotopic system of those samples has occurred over the last 1 Ma, and can be associated with post-magmatic processes, mainly rock-water interactions. All studied samples have (228)Ra/(228)Th ratios equal to unity ±1σ. Consequently, they can be considered to be in secular equilibrium for the last 40 a.

Geochemistry of beach sands from Sithonia Peninsula (Chalkidiki, Northern Greece)

Thirty beach sand samples from the granitic shoreline of the Sithonia Plutonic Complex (SPC) were analyzed for their REE and major element contents. The obtained results are compared with the adjacent SPC rock-types, in order to determine any enrichments or depletions. Among the samples enriched in REE, three are seasonal deposits of heavy minerals and their concentrations are controlled by the action of sea-waves. The available geochemical characteristics were also used to confirm the parental rocks of the beach sands, which are the SPC rock-types. The heavy fractions (total, total magnetic and total non-magnetic) of the beach sands were correlated with the REE concentrations, revealing a strong correlation between the heavy non-magnetic fraction and REE content. Among the minerals of the heavy non-magnetic fraction, monazite seems to control the REE content in the heavy mineral-enriched samples, whereas in the rest of the samples allanite, belonging to the heavy magnetic fraction may be the most important REE mineral.

Natural radioactivity and dose assessment of granitic rocks from the Atticocycladic Zone (Greece)

The activity concentrations of 238 U, 232 Th and 40 K of granite samples taken from the Atticocycladic Zone were measured by gamma-ray spectrometry. These concentrations were compared to the commercial granites imported in Greece and Cyprus. The absorbed, the annual effective dose and the gamma-ray index were determined, so as to assess the radiological impact from the granites investigated, in case they were used as building materials. The range of the absorbed dose rate, the annual effective dose and the gamma index was around a mean value of 86 ± 30 nGy h -1 , 0.6 ± 0.2 mSv y -1 and 1.0 ± 0.2, respectively. Taking into consideration the internal exposure due to radon inhalation, the annual effective dose, in a room fully constructed by granite, varies between 0.4 and 1.4 mSv y -1 . Consequently, since the contribution of the granitic rocks to the total mass of most of the constructions is very low, the samples investigated could be used safely as building materials.

Geochemistry of beach sands from Kavala, Northern Greece

Thirty-seven beach sand samples from the shoreline close to Kavala pluton were analyzed for REE and major element contents. Results are compared with the adjacent plutonic rock-types, in order to determine any enrichments or depletions. Among the samples, several are significantly enriched in REE, being seasonal deposits of heavy minerals and their concentrations are controlled by the action of sea-waves and local winds. The available geochemical characteristics were also used to confirm the parent rocks of the beach sands, which were the rock-types of the Kavala pluton. The heavy fractions (total, total magnetic and total non-magnetic) of the beach sands are moderately correlated with the REE concentrations. Among the minerals of the heavy non-magnetic fraction, allanite seems to control the REE content in the heavy mineral-enriched samples.

Natural radioactivity distribution and gammaradiation exposure of beach sands close to Kavalapluton, Greece

Abstract This study aims to evaluate the activity concentrations of 238U, 226Ra, 232Th, 228Th and 40K along the beaches of Kavala being adjacent to the rock-types of the Kavala pluton. These ranged from 14–940, 16–1710, 26– 4547, 27–4488 and 194–1307 Bq/kg respectively, representing the highest values of natural radioactivity measured in sediments of Greece. The (%wt.) heavy magnetic (HM) (allanite, amphibole, mica, clinopyroxene, magnetite and hematite) fraction, the heavy non-magnetic (HNM) (monazite, zircon, titanite and apatite) fraction and the total heavy fraction (TH), were correlated with the concentrations of the measured radionuclides in the bulk samples. The heavy fractions seem to control the activity concentrations of 238U and 232Th of all the samples, showing some local differences in the main 238U and 232Th mineral carrier. The measured radionuclides in the beach sands were normalized to the respective values measured in the granitic rocks, which are their most probable parental rocks, so as to provide data upon their enrichment or depletion. The annual equivalent dose varies between 0.01 and 0.35 mSv y−1 for tourists and from 0.03 to 1.48 mSv y−1 for local people working on the beach.

Concentration of 238U and 232Th among constituent minerals of two igneous plutonic rocks exhibiting elevated natural radioactivity levels

The concentrations of 238U and 232Th of the constituent minerals in two plutonic rock samples, from N. Greece, exhibiting elevated levels of bulk rock natural radioactivity were determined by using LA-ICP-MS. The available data of whole rock 238U and 232Th concentrations were also used. The minerals were separated using a combination of heavy liquids of various densities, shaking table and magnetic separation techniques. The great variation in the concentrations of 238U and 232Th is probably indicative of the different distribution of U and Th within the same rock, as well as to secondary post-magmatic processes that were responsible for the redistribution of U and Th. An estimation of the contribution of each mineral constituent to the natural radioactivity levels of the bulk rock is attempted. Thorite and zircon contribute the most to the whole rock 238U and 232Th content, while the contribution of apatite is moderate. The contribution of the rest of the minerals examined (fluorite, quartz, plagioclase, K-feldspar, amphibole, pyroxene, magnetite and biotite) is not important.

K/Ar mineral geochronology of the northern part of the Sithonia Plutonic Complex (Chalkidiki, Greece): implications for its thermal history and geodynamic interpretation

Abstract 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