A. Koroneos

The Miocene granitoid rocks of Mt. Bukulja (central Serbia): evidence for pannonian extension-related granitoid magmatism in the northern Dinarides

The study presents evidence about the origin and evolution of the Miocene (20–17 Ma) granitoid pluton of Mt. Bukulja, situated within the southern Pannonian/northern Dinarides region (central Serbia, south-central Europe). The pluton is composed of slightly peraluminous two-mica granite (TMG), metaluminous hornblende-biotite and biotite-bearing (H-BG) granite and rare aplite granite. A lamprophyre dyke (BLD) similar in composition and age to other Serbian primitive minettes has been found in the vicinity of Mt. Bukulja. The available and newly determined radiometric age suggests that the TMG was emplaced around 20 Ma whereas the age of the H-BG is inadequately constrained. TMG and H-BG show similar petrographic characteristics but evidence of open system magma processes is found only in the H-BG. In comparison to the H-BG, the TMGs are less enriched in most trace elements, including REE, and have a more fractionated REE-pattern and stronger negative Eu-anomaly. The TMGs display a wider range of initial Sr-Nd isotope ratios (87Sr/86Sr20 Ma = 0.70652–0.71368 and 143Nd/144Nd20 Ma = 0.51223–0.51283) than the H-BG (87Sr/86Sr20 Ma = 0.70768–0.70781 and 143Nd/144Nd20 Ma = 0.51242–0.51256). Geochemical modeling suggests that the H-BG could have derived from a BLD-like melt by mixing plus fractionation processes assuming a batch of TMG-like magma as the acid end-member. On the other hand, the geochemical variability of the TMG is reproduced by an AFC model with an assimilation/fractionation ratio ( r ) of 0.5 and with high amount of crustal component (~20–50 %) starting from the least evolved TMG rocks. In the modeling, the average composition of the least evolved TMG samples was used to represent the parental magma composition whereas the composition of adjacent metamorphic rocks was adopted as possible contaminant. The composition of the least evolved TMG implies that the TMG parental magma likely originated by melting of a mafic lithology such as earlier basalts underplating in the lower crust. The high proportions of crustal assimilation along with other geochemical and geological evidence suggest that the Mt. Bukulja TMG originated within the same geotectonic setting as acid volcanics of the north Pannonian Basin. The results of this study support the hypothesis that the Mt. Bukulja pluton is related to tectonomagmatic events controlled by the early extensional phases in the opening of the Pannonian basin.

Petrogenetic and tectonic inferences from the study of the Mt Cer pluton (West Serbia)

The Mt Cer Pluton, Serbia, is a complex laccolith-like intrusion (~ 60 km 2 ), situated along the junction between the southern Pannonian Basin and northern Dinarides. It intrudes Palaeozoic metamorphic rocks causing weak to strong thermal effects. Based on modal and chemical compositions, four rock-types can be distinguished: (1) metaluminous I-type quartz monzonite/quartz monzodiorite (QMZD); (2) peraluminous S-type two-mica granite (TMG), which intrudes QMZD; (3) Stražanica granodiorite/quartz monzonite (GDS); and (4) isolated mafic enclaves (ME), found only in QMZD. 40 K– 39 Ar dating and geological constraints indicate that the main quartz monzonite/quartz monzodiorite body of Mt Cer was emplaced not later than 21 Ma, whereas the emplacement ages of the Stražanica granodiorite/quartz monzonite and two-mica granites are estimated at around 18 and 16 Ma, respectively. The Mt Cer pluton is similar to the Mt Bukulja pluton, some 80 km southwestwards. Genesis of QMZD cannot be interpreted by fractional crystallization coupled with mixing or assimilation. It is best explained by a convection–diffusion process between mantle-derived minette/leucominette magmas and GDS-like magmas followed by two end-member magma mixing. The composition of GDS rocks suggests that GDS-like magmas could have formed by melting of lower crustal lithologies similar to amphibolite/metabasalts. The geochemistry of TMG is reproduced by an Assimilation/Fractional Crystallization model with a ratio of rate of assimilation to rate of fractional crystallization of 0.4, using the compositions of the least evolved TMG of the Bukulja pluton and adjacent metamorphic rocks as proxies for the parental magma and contaminant, respectively. The origin and evolution of the Mt Cer and adjacent Mt Bukulja plutons provide new constraints on the Tertiary geodynamics of the northern Dinarides–southern Pannonian region. The quartz monzonite/quartz monzodiorite is interpreted as a result of the Oligocene post-collisional Dinaride orogen-collapse, which included a limited lithosphere delamination, small-scale mantle upwelling, and melting of the lower crust. By contrast, the two-mica granite magmas formed through melting in shallower crustal levels during the extensional collapse in the Pannonian area.

Natural radioactivity and radiation index of the major plutonic bodies in Greece.

The natural radioactivity of the major plutonic bodies in Greece, as well as the assessment of any potential health hazard due to their usage as decorative building materials is studied. One hundred and twenty one samples from every major plutonic body in Greece, including various rock-types from gabbro to granite, have been measured for their natural radioactivity using γ-spectrometry methodology. According to the experimental results, the natural radioactivity levels were ranged up to 315xa0Bqxa0kg(-1) for (226)Ra, up to 376xa0Bqxa0kg(-1) for (232)Th and up to 1632xa0Bqxa0kg(-1) for (40)K, with arithmetic mean values and standard deviations of 74 (±51), 85 (±54) and 881 (±331) Bqxa0kg(-1) respectively, which are below the international representative mean values for granite stones. The excess on the effective dose received annually indoors due to granite tiles usage is estimated considering a standard room model where granite tiles with 1.5xa0cm in thickness cover only the floor of the room. The increment on the external γ-radiation effective dose rate shows a Gaussian distribution well dispersed below 0.3xa0mSvxa0y(-1), presenting a mean value of 0.14 (±0.06)xa0mSvxa0y(-1). In case of the internal α-radiation a log-normal distribution is appeared scattering below 0.5xa0mSvxa0y(-1) with a mean value 0.19 (±0.13)xa0mSvxa0y(-1), for a well-ventilated living environment. In case of a poor-ventilated room the increment on internal effective dose rate is estimated with a mean value 0.27 (±0.19)xa0mSvxa0y(-1) scattering below 0.8xa0mSvxa0y(-1). The majority of the samples increase the external as well as the internal dose less than 30% of the maximum permitted limit of the effective dose rate. Therefore, at least from radiological point of view, the plutonic rocks of Greece could be safely used as decorative building materials.

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.

Geochemistry and Petrogenesis of Post-Collision Pangeon Granitoids in Central Macedonia, Northern Greece

Abstract The Pangeon granitoids in northern Greece are intrusive into metamorphic rocks of the Lower Tectonic Unit of the Rhodope Massif. They are characterized by two distinct petrological types: A medium- to coarse-grained porphyritic, hornblende-biotite bearing tonalite to granodiorite (PTG), and a fine- to medium-grained biotite granodiorite to two-mica granite (MGG). Biotite-hornblende bearing mafic microgranular enclaves of monzodioritic composition (MME) are present in the PTG rocks. The granitoids have characteristics of high-K calc-alkaline metaluminous (PTG) to slightly peraluminous (MGG) rocks. The sharp contacts between the two types and the different compositional trends shown by them indicate the existence of two magma pulses. It is considered that partial melting of the same source rock, but under different P-T conditions, produced the magma pulses. These conditions were slightly higher for the PTG rocks than the MGG ones. The chemical variations within each group suggest a major crystal fractionation, accompanied by contamination. The Pangeon granitoids are enriched in K, Rb, Ba and Th relative to Nb, Zr, Sm and resemble post-collisional granites.

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