U-Pb isotopic study of the gabbronorite–anorthosite drusite (coronite) body of Vorony Island (Kandalaksha Archipelago,the White Sea)

The Precambrian Belomorian mobile belt located between the Karelian craton and the Lapland–Umba granulite belt contains large amount of small rootless mafic–ultramafic intrusions, which are dispersed over a large area and distinguished as the Belomorian drusite (coronite) complex. U-Pb dating of magmatic zircon and metamorphic rutile from the drusite body on Vorony Island showed that it was crystallized at 2460 ± 11 Ma and metamorphosed at 1775 ± 45 Ma. Petrographic and geochemical data confirm that the parental magmas of the drusites belong to the siliceous high-magnesian (boninite-like) series, which also was responsible for the formation of large layered plutons in stable domains of the Baltic Shield.     

Evolution of hydrothermal fluids of HS and LS type epithermal Au–Ag deposits in the Seongsan hydrothermal system of the Cretaceous Haenam volcanic field,South Korea

The Haenam volcanic field was formed in the southern part of the Korean peninsula by the climactic igneous activity of the Late Cretaceous. The volcanic field hosts more than nine hydrothermal clay deposits and two epithermal Au–Ag deposits. This study focuses on the relationship between hydrothermal clay alteration and epithermal Au–Ag mineralization based on the geology, alteration mineralogy, geochronology, and mineralization characteristics.These clay and epithermal Au–Ag deposits are interpreted to have formed by the same hydrothermal event which produced two distinct types of mineral systems: 1) Au-dominant epithermal Au–Ag deposit and 2) clay-dominant hydrothermal clay deposit. The two types of mineral systems show a close genetic relationship as suggested by their temporal and spatial relationships. The Seongsan hydrothermal system progressively evolved from a low-intermediate sulfidation epithermal system with Au–Ag mineralization and phyllic alteration to an acid–sulfate high-sulfidation system with Au–Ag mineralization and/or barren advanced argillic/argillic alteration. The Seongsan system evolved during post volcanic hydrothermal activity for at least 10 Ma in the Campanian stage of the late Cretaceous.The Seongsan hydrothermal system shows the rare and unique occurrence of superimposed high to low (intermediate) sulfidation episodes, which persisted for about 10 Ma.     

An integrated zircon geochronological and geochemical investigation into the Miocene plutonic evolution of the Cyclades, Aegean Sea, Greece: part 2—geochemistry

Zircons from 14 compositionally variable granitic rocks were examined in detail using CL image-guided micro-analysis to unravel the complex magmatic history above the southward retreating Hellenic subduction zone system in the Aegean Sea. Previously published U–Pb ages document an episodic crystallisation history from 17 to 11?Ma, with peraluminous (S-type) granitic rocks systematically older than closely associated metaluminous (I-type) granitic rocks. Zircon O- and Hf isotopic data, combined with trace element compositions, are highly variable within and between individual samples, indicative of open-system behaviour involving mantle-derived melts and evolved supracrustal sources. Pronounced compositional and thermal fluctuations highlight the role of magma mixing and mingling, in accord with field observations, and incremental emplacement of distinct melt batches coupled with variable degrees of crustal assimilation. In the course of partial fusion, more fertile supracrustal sources dominated in the earlier stages of Aegean Miocene magmatism, consistent with systematically older crystallisation ages of peraluminous granitic rocks. Differences between zircon saturation and crystallisation temperatures (deduced from zircon Ti concentrations), along with multimodal crystallisation age spectra for individual plutons, highlight the complex and highly variable physico-compositional and thermal evolution of silicic magma systems. The transfer of heat and juvenile melts from the mantle varied probably in response to episodic rollback of the subducting lithospheric slab, as suggested by punctuated crystallisation age spectra within and among individual granitic plutons.     

Timing of multiple hydrothermal events in the iron oxide–copper–gold deposits of the Southern Copper Belt,Carajás Province,Brazil

The Southern Copper Belt, Carajás Province, Brazil, hosts several iron oxide–copper–gold (IOCG) deposits, including Sossego, Cristalino, Alvo 118, Bacuri, Bacaba, Castanha, and Visconde. Mapping and U–Pb sensitive high-resolution ion microprobe (SHRIMP) IIe zircon geochronology allowed the characterization of the host rocks, situated within regional WNW–ESE shear zones. They encompass Mesoarchean (3.08–2.85 Ga) TTG orthogneiss, granites, and remains of greenstone belts, Neoarchean (ca. 2.74 Ga) granite, shallow-emplaced porphyries, and granophyric granite coeval with gabbro, and Paleoproterozoic (1.88 Ga) porphyry dykes. Extensive hydrothermal zones include albite–scapolite, biotite–scapolite–tourmaline–magnetite alteration, and proximal potassium feldspar, chlorite–epidote and chalcopyrite formation. U–Pb laser ablation multicollector inductively coupled mass spectrometry (LA-MC-ICP-MS) analysis of ore-related monazite and Re–Os NTIMS analysis of molybdenite suggest multiple Neoarchean (2.76 and 2.72–2.68 Ga) and Paleoproterozoic (2.06 Ga) hydrothermal events at the Bacaba and Bacuri deposits. These results, combined with available geochronological data from the literature, indicate recurrence of hydrothermal systems in the Southern Copper Belt, including 1.90–1.88-Ga ore formation in the Sossego–Curral ore bodies and the Alvo 118 deposit. Although early hydrothermal evolution at 2.76 Ga points to fluid migration coeval with the Carajás Basin formation, the main episode of IOCG genesis (2.72–2.68 Ga) is related to basin inversion coupled with Neoarchean (ca. 2.7 Ga) felsic magmatism. The data suggest that the IOCG deposits in the Southern Copper Belt and those in the Northern Copper Belt (2.57-Ga Salobo and Igarapé Bahia–Alemão deposits) do not share a common metallogenic evolution. Therefore, the association of all IOCG deposits of the Carajás Province with a single extensive hydrothermal system is precluded.     

Oxygen,carbon and sulphur isotope studies in the Keban Pb–Zn deposits,eastern Turkey: An approach on the origin of hydrothermal fluids

Pb–Zn deposits are widespread and common in various parts of the Taurus Belt. Most of the deposits are of pyrometasomatic and hydrothermal origin. The Keban Pb–Zn deposits are located along the intrusive contact between the Paleozoic – Lower Triassic Keban Metamorphic Formation and the syenite porphyry of the Upper Cretaceous Keban igneous rocks. Various studies have already been carried out; using fluid inclusion studies on fluorite, calcite and quartz on the pyrite–chalcopyrite bearing Keban ore deposits. This study focuses on the interpretation of stable isotope compositions in connexion with fluid inclusion data. Sulphur isotope values (δ³⁴S) of pyrite are within the range of ?0.59 to +0.17‰_V-CDT (n = 10). Thus, the source of sulphur is considered to be magmatic, as evidenced by associated igneous rocks and δ³⁴S values around zero“0”. Oxygen isotope values δ¹⁸O of quartz vary between +10.5 and +19.9‰_(SMOW). However, δ¹⁸O and δ¹³C values of calcite related to re-crystallized limestone (Keban Metamorphic Formation) reach up to +27.3‰_(SMOW) and +1.6‰_(PDB), respectively. The δ³⁴S, δ¹³C and δ¹⁸O values demonstrate that skarn-type Pb–Zn deposits formed within syeno-monzonitic rocks and calc-schist contacts could have developed at low temperatures, by mixing metamorphic and meteoric waters in the final stages of magmatism.     

Recurrent hydrothermal activity induced by successive extensional episodes: the case of the Berta F–(Pb–Zn) vein system (NE Spain)

A mineralogical and geochemical (fluid inclusion, stable and radiogenic isotopes) study of the Berta F–(Pb–Zn) vein system has identified the source and temperature of the fluid reservoirs involved and proved the existence of two separate hydrothermal events at the mine scale, which reflect distinct periods of regional fluid circulation. Main stage minerals (fluorite I, sulphides, calcite I and barite I) precipitated by mixing between a polysaline H₂S bearing (δ³⁴S=11‰) brine (up to 23% NaCl eq salinity) and a more dilute fluid (δ¹⁸O from −3.2‰ to 0‰), at temperatures between 80 and 150°C. The progressive increase in ⁸⁷Sr/⁸⁶Sr ratio from the early precipitated minerals (0.71242 in calcite I) to the late ones (0.71894 in fluorite II) is mainly (but not exclusively) due to a difference in age separating the two hydrothermal events. The assumed genetic model for the main stage fluorite (I) is based on a convective circulation of surficial waters leaching the crystalline basement rocks acquiring a high salinity, high ⁸⁷Sr/⁸⁶Sr ratios and a high temperature. These fluids then mixed with low salinity–low temperature waters, having a low ⁸⁷Sr/⁸⁶Sr ratio. An at least Jurassic age is suggested for the main period of vein filling, contemporaneous with the extensional regime during the Mesozoic, when fluid circulation was probably enhanced by crustal thinning. During the early Burdigalian (lower Miocene), a new period of important extension in this area took place. Hydrothermal activity related to this new and younger extensional regime is geochemically different and produced a distinctive mineralogical record, developing a set of veinlets filled with green octahedral fluorite (fluorite II), calcite (II) and barite (II). The Sr isotope compositions of these late stage vein minerals are compatible with leaching the granodiorite host-rocks during recent times. The existence of successive hydrothermal events in the same area is not surprising as geothermal systems, like La Garriga–Samalus, are still active and currently precipitating fluorite.     

Phytoplankton,protozooplankton and nutrient dynamics in the Bornholm Basin (Baltic Sea) in 2002–2003 during the German GLOBEC Project

From March 2002 to until April 2003 we investigated the seasonal nutrient and phytoplankton dynamics in the central Bornholm Basin (Baltic Sea) within the framework of the German GLOBEC Project. We choose a nested approach consisting of vertical fluorescence profiles, phytoplankton counts and nutrient analyses. The Fluoroprobe (MultiProbe, BBE Moldaenke) is capable of distinguishing four algal groups (Cryptophyceae, Cyanophyceae, Chlorophyceae, Bacillariophyceae + Dinophyceae). Winter nutrient concentrations were about 5 μM NO₃ and 0.5 μM PO₄ in the central Basin. The spring phytoplankton bloom was dominated by the diatom Skeletonema sp. and reached a maximum of about 270 μg C/l before the onset of the seasonal stratification. Protozooplankton was dominated by the Mesodinium rubrum (a phototrophic ciliate = Myrionecta rubra) and reached a maximum biomass of about 200–300 μg C/l about 2 weeks after the demise of the diatom spring bloom. During summer, the water column was stratified and a subsurface maximum developed near the thermocline consisting of Bacillariophyceae, Cryptophycea and other phototrophic flagellates. Phytoplankton and protozooplankton biomass was generally low. Nutrient concentrations point towards a nitrogen limitation during this period. The stratification period ended during September and surface nutrient concentrations increased again. Protozooplankton reached a second maximum during September. With the Fluoroprobe small scale structures in the plankton community could be detected like a subsurface Cryptophyceae maximum near the thermocline that however, could not be confirmed by cell counts. The chlorophyll a estimate of the Fluoroprobe was in good agreement with the phytoplankton biomass estimated from counts. We conclude that only by combining modern sensing technology with microscopy, the small-scale dynamics and taxonomic spectrum of the plankton can be fully captured.     

Pressure–temperature evolution of eclogites from the Kechros complex in the Eastern Rhodope (NE Greece)

The Rhodope Domain in NE Greece consists of different tectonometamorphic complexes involved in the Alpine collisional history between the Eurasian and African plates. In the Kechros Complex, which is the lowermost tectonic unit in the East Rhodope, a lense of kyanite eclogite occurs within orthogneiss and common eclogites are found between serpentinized peridotite and underlying pelitic gneisses. In kyanite eclogite, the high-pressure (HP) mineral assemblage is Grt?+?Omp (Jd_35–55)?+?Ky?+?Ph?+?Qz?+?Rt?+?(indirectly inferred Tlc?+?Law); a Na-rich tremolite and zoisite formed at or near peak metamorphic conditions. In common eclogites, the HP mineral assemblage is Grt?+?Omp (Jd29–41)?+?Rt and, with less certainty, Amp (Gln-rich?+?Brs?+?Wnc?+?Hbl)?±?Czo. The inclusions in garnet are glaucophane, actinolite, barroisite, hornblende, omphacite, clinozoisite, titanite, rutile and rarely paragonite and albite. In kyanite eclogite, peak P–T conditions are constrained at 2.2?GPa and 615°C using garnet–omphacite–phengite geothermobarometry and very similar values of 585?±?32°C and 2.17?±?0.11?GPa with the average P–T method, by which conditions of formation could also be narrowed down for the common eclogite (619?±?53°C and 1.69?±?0.17?GPa) and for a retrogressed eclogite (534?±?36°C and 0.77?±?0.11?GPa). Ages for the HP metamorphism in the Kechros Complex are not yet available. A Rb–Sr white mica age of 37?Ma from orthogneiss records a stage of the exhumation. The HP event may be coeval with the Eocene HP metamorphism (49–55?Ma) recorded in the Nestos Shear Zone in Central Rhodope and in the Attic-Cycladic crystalline belt, where it is interpreted as the result of subduction and final closure of the Axios/Vardar ocean and subsequent subduction of the Apulian continental crust (a promontory of the Africa continent) under the southern margin of the European continent in the late Cretaceous and early Tertiary.     

The nationalization of electoral change in a geographical perspective: the case of Italy (2006–2008)

This paper assesses the nationalization of electoral change in a setting of major changes at the party level. After discussing the theoretical difference between the configuration of the electorate and its movement, the Italian case is examined. In order to check whether strategic voting dynamics took place between the 2006 and 2008 Italian Parliamentary elections, the swing voters’ estimates are obtained. After having shown that the Italian electorate behaved strategically, we investigated whether the swing had a national or a territorial pattern. The findings show that the switching occurred in Italy between the 2006 and the 2008 elections can be considered national.     

Dual impact on the groundwater aquifer in the Kazan Plain (Ankara, Turkey): sand–gravel mining and over-abstraction

This study explains the impact of sand–gravel mining and over-abstraction, and the response of the groundwater system in the Kazan Plain, Turkey. The plain used to be known for its fresh groundwater potential, valuable agricultural lands and natural beauty until the 1980s. According to the estimation in 1975, there was 15.5 million m³ annual useable freshwater in the Quaternary sand–gravel aquifer. Groundwater level ranged between 0 and 5 m from the surface of the plain in the 1970s. Because of the large and deep excavations by the sand–gravel pits during the past 25–30 years, the aquifer has thinned and removed entirely in some places. In addition, over-abstraction has accelerated the decline of the groundwater level, particularly in the middle and the upper part of the plain in recent years. As of 2009, about 12% of the total volume of the aquifer area removed by the pits and groundwater table has been reduced to between 5 and 20 m. The decline of the water table reaches 15–20 m in the regions where over-abstraction has taken place. To reduce the hazards to the groundwater system, the sand–gravel pits have to be banned immediately, a reclamation project applied and abstraction must be reduced.     

Freeze–thaw cycles and rainfall as triggering factors of mass movements in a warm Mediterranean region: the case of the Tramuntana Range (Majorca, Spain)

Between 2008 and 2010, the island of Majorca (Spain) experienced the coldest and wettest winters of the last 40 years. Accumulated rainfall was twice the average and values of intense rainfall up to 296 mm/24?h were recorded, very similar to those calculated for a return period of 100 years. Additionally, high precipitation coincided with anomalous, low temperatures, with abundant snowfall and freezing in the highest zones of the Tramuntana Range, in the northwest sector of the island. As a result, 34 mass movements were recorded on the range, which seriously affected the road network in an area of great importance for tourism, as it welcomes 8.5 million visitors each year. Fourteen rockfalls, 1 rock avalanche, 15 landslides and 4 karstic collapses were inventoried. The geological structure, formed by a series of NW overlapping thrusts, determines the distribution as well as the failure pattern of the movements. Thus, the northern face of the range registered 68% of the mass movements: nine rockfalls with planar failure took place as well as all the landslides recorded. Likewise, south-facing slopes have been affected by longer runout rockfalls with a wedge-type failure. The thorough analysis of the meteorological data shows that most of the movements have taken place after antecedent rainfall over 800?mm. Additionally, the rockfalls have also occurred after several freeze–thaw cycles, being a determining and unusual factor in this warm region. Intense rainfall >90 mm/24?h also caused rockfalls as well as exceptional very intense rainfall >120 mm/24?h caused landslides. The results aim to contribute to the design of an early warning system coordinating emergency, infrastructure services and meteorological centres in a region of high risk.     

Origin and evolution of hydrothermal fluids in the Taochong iron deposit,Middle–Lower Yangtze Valley,Eastern China: Evidence from microthermometric and stable isotope analyses of fluid inclusions

The Middle–Lower Yangtze River Valley is one of the most important metallogenic belts in China, hosting numerous Cu–Fe–Au–Mo deposits. The Taochong deposit is located in the northern part of the Fanchang iron ore district of the Middle–Lower Yangtze River metallogenic belt. The Fe-orebody is hosted by Middle Carboniferous to Lower Permian limestones. Skarns and Fe-orebodies occur as tabular bodies along interlayer-gliding faults, at some distance from the inferred granitic intrusions. Field evidence and petrographic observations indicate that the three stages of hydrothermal activity—the skarn, iron oxide (main mineralization stage), and carbonate stages—all contributed to the formation of the Taochong iron deposit. The skarn stage is characterized by the formation of garnet and pyroxene, with high-temperature, hypersaline hydrothermal fluids with isotopic compositions similar to those of typical magmatic fluids. These fluids were probably generated by the separation of brine from a silicate melt instead of the product of aqueous fluid immiscibility. The iron oxide stage coincides with the replacement of garnet and pyroxene by actinolite, chlorite, quartz, calcite and hematite. The hydrothermal fluids at this stage are represented by saline fluid inclusions that coexist with vapor-rich inclusions with anomalously low δD values (− 66‰ to − 94‰). The decrease in ore fluid δ¹⁸O_water with time and decreasing depth is consistent with the decreases in fluid salinity and temperature. The fluid δD values also show a decreasing trend with decreasing depth. Both fluid inclusion and stable isotopic data suggest that the ore fluid during the main period of mineralization was evolved by the boiling of various mixtures of magmatic brine and meteoric water. This process was probably induced by a drop in pressure from lithostatic to hydrostatic. The carbonate stage is represented by calcite veins that cut across the skarn and orebody, locally producing a dense stockwork. This observation indicates the veins formed during the waning stages of hydrothermal activity. The fluids from this stage are mainly represented by a variety of low-salinity fluid inclusions, as well as fewer high-salinity inclusions. These particular fluids have the lowest δ¹⁸O_water values (− 2.2‰ to 0.4‰) and a wide of range of δD values (− 40‰ to − 81‰), which indicate that they were originated from a mixture of residual fluids from the oxide stage, various amounts of meteoric water, and possibly condensed vapor. Low-temperature boiling probably occurred during this stage.We also discuss the reasons behind the anomalously low δD values in fluid inclusion water extracted by thermal decrepitation from quartz at high temperatures, and suggest that calcite data provide a possible benchmark for adjusting low δD values found in quartz intergrown with calcite.     

Evaluation of earthquake-induced strain in promoting mud eruptions: the case of Shamakhi–Gobustan–Absheron areas,Azerbaijan

Although a relationship between the occurrence of large earthquakes and the eruptions of close mud volcanoes is well known, several uncertainties remain on understanding the triggering mechanisms. In the present study, we evaluate both the static and dynamic strains induced by earthquakes in the substratum of mud volcanoes. We studied the effects of two earthquakes of M _w 6.18 and 6.08 occurred in the Caspian Sea on 25 November 2000 close to Baku city, Azerbaijan. A total of 33 eruptions occurred at 24 mud volcanoes within a maximum distance of 108 km from the epicentres in the 5 years following the earthquakes. The overall eruption rate in the studied area of the 50 years before the 2000 earthquakes was 1.24 that is much smaller than the eruption rate of 6.6 of the 5 years following these earthquakes. The largest number of eruptions occurred within 2 years from the earthquakes with the highest frequency within 6 months. Our calculated earthquake-induced static effects show that crustal dilatation might have triggered only seven eruptions at a maximum distance of about 60 km from the epicentres and within 3 years. Based on our data, dynamic rather than static strain is likely to have been the dominating “promoting” factor because it affected all the studied unrest volcanoes and its magnitude was much larger.     

Unique location of hydrothermal biota in the Lower Cambrian sedimentary-volcanogenic complex of the Kyzyl–Tashtyg ore field (Eastern Tuva)

Study of Early Cambrian sedimentary-volcanogenic complexes hosting the Kyzyl–Tashtyg pyrite deposit in Eastern Tuva has revealed cyanobacteria and algae that existed in zones of ore-forming hydrothermal systems similar in characteristics to present-day “black smokers” at ocean bottoms. Along with archaeocyaths and Cyanophyta from the host sedimentary rocks and microfossils from basalt amygdules, various cyanobacteria, monocyatheans, and sponge spicules have been found in ferrosiliceous deposits and metasedimentary rocks. Scanning electron microscopic, mineralogical, and thermobarogeochemical studies helped to reconstruct their hydrothermal environment.     

Groundwater chemistry of strike slip faulted aquifers: the case study of Wadi Zerka Ma’in aquifers, north east of the Dead Sea

Wadi Zerka Ma’in catchment area is located to the north east of the Dead Sea. It has two types of aquifers: (a) an upper unconfined aquifer and (b) a lower confined aquifer. The two aquifers are separated by a marl aquiclude. A major strike slip fault passes perpendicularly through the two aquifers and the aquiclude layer with embedded normal faults. The aim of the study was to specify the effect of the major strike slip fault on the groundwater chemistry. The spatial variability of the hydrochemical compositions and physiochemical parameters of the groundwater were investigated. It was found that the embedded normal faults, of the strike slip fault, form conduits that allow groundwater to flow from the lower aquifer to the upper aquifer, resulting in mixed groundwater. The ratio of mixing was estimated to be 94 % groundwater from the upper aquifer and 6 % from the lower aquifer. Since groundwater in the lower aquifer is around three times more saline than the upper aquifer, water mixing into the upper water aquifer generates a salinity hazard.     

Hydrocarbons in the Basement of the South China Sea (Vietnam) Shelf and Structural–Tectonic Model of their Formation

Geotectonics - The paper considers the origin of hydrocarbon accumulations within the Pre-Cenozoic basement of the Vietnam shelf. It is shown that the formation of hydrocarbon deposits is...