Petrogenesis of the Upper Jurassic Monopigadon pluton related to the Vardar/Axios ophiolites (Macedonia,northern Greece) and its geotectonic significance

The origin, evolution and geotectonic setting of the Upper Jurassic Monopigadon granitoid pluton (Chalkidiki, Central Macedonia) are studied. The pluton is composed of slightly peraluminous to peraluminous high-K calc-alkaline biotite granodiorite (BGrd), biotite granite (BGr), leucogranite (LGr) and aplites (Apl). Enclosed rocks (Enc) are mostly xenoliths, surmicaceous enclaves and biotite clots occurring frequently in BGrd and BGr. Serpentinite bodies as well as amphibolite and calc-silicate hornfelses are exposed as inliers in the pluton. The granitoids are characterized by relatively low Sr contents (<180 ppm) and low Sr/Y ratio (0.4–6.4). REE are enriched in the granitic rocks (La_CN=89–148, Lu_CN=6–25) and the enclaves (La_CN=19–55, Lu_CN=15–18). The (La/Lu)_CN ratio ranges from 10.5 to 4.9 in BGrd, from 11.1 to 3.8 in BGr and from 11.3 to 25.7 in LGr. The BGrd and BGr show similar LILE-enriched, spiked patterns with negative anomalies at Ba, Ta, Nb, Sr and Ti and a positive anomaly at Pb, while the patterns of LGr show higher Ta, Nb, Sr, Ti negative and Pb positive anomalies. Sr initial isotopic ratios vary from 0.7147 to 0.7174 in BGrd, are relatively constant at 0.7105–0.7113 in BGr, and range from 0.7213 to 0.7340 in LGr, while they are lower in the enclaves (0.7087–0.7094). BGrd shows the lowest ε_Nd values (?8.31 to ?6.43), while it ranges from ?6.11 to ?4.26 in BGr and from ?3.37 to ?0.89 in LGr. Late Triassic to Late Jurassic intrusion zircon ages are reported for the Monopigadon pluton, which is unconformably overlain by Kimmeridgian–Tithonian limestones, whereas fragments of the plutonic rocks occur in the limestones. The geochemical variability of the BGrd is reproduced by two different AFC models having the same parental magma and assimilation/fractionation ratio but different assimilated end members. Geochemical modelling suggests that the BGr variability could be reproduced by two different FC models having the same parental magma but with different fractionating assemblages. The BGrd and BGr have similar sources and they likely originated by partial melting of middle-lower crustal rocks with intermediate-basaltic compositions, such as amphibolites, andesites and basalts. Felsic garnet granulites and metapelites are candidate source rocks for LGr. It is suggested that the Monopigadon plutonic rocks originated by melting of an inhomogeneous crust in a volcanic arc environment due to the heating of mantle-derived magmas, which, however, had not mixed or mingled with the crustal melts.     

The effects of pollution-induced oxygen deficiency on the benthos in Elefsis Bay,Greece

Benthic studies in Elefsis Bay, Greece, have shown pronounced seasonal changes in both numbers of species and of individuals. In both winter and summer, abundance and diversity were higher in the western than in the eastern part of the Bay. In summer, abundance and diversity increased in the former and sharply decreased or dropped to zero in the latter. In summer most of the bottom, with an oxygen concentration of less than 1 ml/litre, became almost azoic. With increasing oxygen concentration the numbers of species and individuals increased. The most abundant and frequent winter species were found in summer in reduced numbers at a limited number of stations, all of which were characterised by an oxygen concentration higher than 1 ml/litre.Dominance diversity (H′), as measured by the Shannon-Werner formula, and its species diversity component (d), showed wide differences both spatially and temporally, which coincided with the dissolved oxygen regimes in the Bay. The evenness component (J′) did not seem to be a reliable ‘weighting factor’ of H′ when numbers of species and individuals were low, thus necessitating caution in its use.The values of H′, J′ and d were compared with those of other areas divided into pollution zones based on purely faunistic data. Using the results of these comparisons, Elefsis Bay was divided into pollution zones which, from two in winter (subnormal and polluted), increased to three in summer when an azoic zone was formed.     

Slug test in confined aquifers, the over-damped case: quasi-steady flow analysis

In the great majority of slug tests performed in wells fully penetrating confined geologic formations, and for over-damped conditions, the response data are evaluated with the transient-flow model of Cooper et al. (1967) when the radial hydraulic conductivity K(r) and the coefficient of specific storage S(s) are to be estimated. That particular analytical solution, however, is computationally involved and awkward to use. Thus, groundwater professionals often use a few pre-prepared type-curves to fit the data by a rough matching procedure, visually or computationally. On the other hand, the method of Hvorslev (1951), which assumes the flow to be quasi-steady, is much simpler but yields only K(r) estimates. In this work, we develop a complete quasi-steady flow model that includes a storage balance inside the aquifer and allows estimating K(r) and S(s) simultaneously, through matching of the well response data to a type-curve. The new model approximates the model of Cooper et al. closely and has the practical advantage that its solution type-curves are generated easily using an electronic spreadsheet, so that the optimal fit of data by a type-curve can be readily automated.     

Oxygen-deficient and organic carbon fields expansion in Elefsis Bay,Greece

Benthic studies were conducted in winter and summer 1977 in Elefsis Bay, Greece and in this report the oxygendeficient and the organic carbon fields expansion over the last few years is presented. In summer 1977 the oxygendeficient field has been increased more than two times, as compared to that existing in the summer 1973, covering an area of about 80% of the bottom of the bay. In 1977 most of the bottom consisted of sediment with more than 1% organic carbon. Comparing the results of this study with those of a previously conducted study it is found that the bottom area with organic carbon over 1% has been doubled between 1975 and 1977, covering a similar area to the oxygen-deficient field.