Triantafyllos Soldatos

Corundum primary deposits in Greece occur in four locations: Paranesti in Drama and Gorgona in Xanthi, both belonging to the wider Rhodope Massif, as well as, Ikaria island and Kinidaros in Naxos island, both belonging to Attic-Cycladic Massif. Eight samples were examined with spectroscopic methods (FTIR, UV-Vis, EDXRF) in order to better characterize these four primary deposits: two pink sapphires from Paranesti, a pink and a blue sapphire from Gorgona, two blue sapphires from Ikaria and three blue sapphires from Kinidaros. Under the microscope, all samples present characteristics linked to post-crystallization deformation, decreasing their gem quality. The FTIR absorption spectra of all samples present in different relative intensities, bands of boehmite, diaspore, goethite, mica and/or chlorite inclusions and CO₂ in fluid inclusions. Boehmite and diaspore inclusions are most likely epigenetic. In the UV-Vis spectra, the pink color of the samples is linked with Cr³⁺ absorptions and the blue color with absorptions due to Fe²⁺-Ti⁴⁺ intervalence charge transfer. EDXRF analyses in the studied samples show relatively high titanium and iron concentrations that are related with mineral inclusions. Gallium is slightly variable in samples from different regions; also, different colored samples from Gorgona present diverse gallium content.

Natural K-feldspars from igneous rocks have been examined by means of X-ray powder diffraction(XRPD) and Fourier transform infrared (FTIR) spectroscopy in the spectral range 400-1400 cm-1,where the Si-Al-O bonds exhibit the dominant vibrations. From the XRPD analysis three specieshave been distinguished, i.e. microclines (3 samples), orthoclases (4 samples) and sanidines (3 samples);their unit cell parameters were calculated. The FTIR transmittance spectra of all sampleshave common bands at 426, 463, 584, 604, 726 and 772 cm-1 and some additional features. The spectraof sanidine and orthoclase exhibit fewer and broader bands than the microclines’, especially inthe area 1000-1200 cm-1. The differences in their spectra are located in four bands. The bands ataround 536-538 and 646-648 cm-1 in the spectrum of microcline, are shifted at around 542-544 and640-642 cm-1 in the spectrum of orthoclase and at around 546 and 636 cm-1 in the spectrum of sanidine.Four bands at 1010, 1050, 1090 and 1136 cm-1 in the spectra of microcline are substitutedwith two quite broad bands at about 1030 and 1125 cm-1 in the spectra of orthoclase and sanidine.These differences are attributed to different degree of Al-Si ordering in the structure of K-feldspars.

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