Geochemistry of I-type granitoids in the Karaburun Peninsula, West Turkey: Evidence for Triassic continental arc magmatism following closure of the Palaeotethys

Abstract Triassic granitoids related to Palaeo- and Neo-Tethyan events occur widely in the metamorphic terranes largely affected by the Alpine orogeny. A first recorded unmetamorphosed plutonic body intruded into the Palaeotethyan mélange in western Turkey, called the Karaburun granodiorite, is composed of two small intrusive stocks that were emplaced between 240 and 220 Ma. It is compositionally diverse, ranging from granodiorite and tonalite to diorite. These rocks show heterogeneous compositions with 54 to 65 wt % SiO₂ and are calc-alkaline in character. They are also subalkaline with molar ratios of Al₂O₃/(Na₂O + K₂O) from 0.74 to 1.00 and are metaluminous. Most samples are diopside-normative (0.36–8.64), with Na₂O > K₂O. Chondrite normalized rare earth element (REE) patterns show various degrees of light REE (LREE) enrichment, with La _N = 57.79 to 99.59 and (La/Yb) _N = 5.98–7.85 and Eu negative anomalies (Eu/Eu* = 0.62–0.86). These rocks have coherent patterns in ocean ridge granite (ORG) normalized trace-element plots, marked by variable enrichment in K, Rb, Ba, Th, Ce and depletion in Ta and Nb, similar to I-type granites from subduction zones. In primitive mantle-normalized multi element variation diagrams, the granodiorites show pronounced depletions in the high-field-strength elements (HFSE; Nb, Ta, Zr), Sr, P, and Ti. Trace-element modeling of the Karaburun granodiorite suggests an origin through partial melting of the subduction-modified mantle wedge with minor contribution of crustal components through a process of strong fractional crystallization (FC) combined with slight assimilation-fractional crystallization (AFC). Exposures of typical continental-arc granodiorites in the Karaburun Mélange support the validity of the subduction-accretion model that implies the presence of an active continental margin following closure of the Palaeotethyan Ocean during the Triassic.     

Andesitic magma degassing investigated through H2O vapour–melt partitioning of halogens at Soufrière Hills Volcano, Montserrat (Lesser Antilles)

Magma degassing at Soufrière Hills Volcano (SHV) is characterised by an almost permanent SO₂ flux and a HCl production rate which mainly depends on dome growth rate. Degassing processes have been studied through textural, H₂O and halogen analyses of clasts collected between 1995 and 2006 on the dome and in pyroclastic flows and vulcanian eruption deposits. Cl, Br and I are strongly depleted in melts during H₂O degassing with no significant Cl–Br–I fractionation, whereas F is almost unaffected. All magmas erupted at SHV have followed a multi-step degassing path from the magma chamber up to a shallow depth ( 1 km, P  20 MPa). From that depth, however, effusive and explosive paths are distinct; vulcanian eruptions are the result of closed system degassing (CSD), while effusive dome growth is the result of CSD up to a very shallow depth (≤ 200 m, P  5–2 MPa) followed by open system degassing (OSD). CSD is modelled using the H₂O solubility law, the perfect gas law and partition coefficients of halogens between a rhyolitic melt and H₂O vapour (d_v − lⁱ). Gas loss characteristic of OSD is modelled using a Rayleigh law. Degassing induced crystallisation is introduced through the ratio of crystallisation and degassing rates, which ranges from 150–500. d_v − l^Cl for OSD ranges between 50–300, increasing with melt Cl content. For CSD, the lower effective d_v − l^Cl ( 20) is attributed to kinetic effects.

Dome forming activity has a greater impact on atmospheric chemistry than vulcanian eruptions because OSD is much more efficient at extracting halogens. The model shows that HCl flux is a good proxy for the dome forming eruption rate. Comparison between model and measured gas compositions suggests a high HBr–BrO conversion rate (BrO/Total Br  1/3) in the SHV gas plume.

The degassing behaviour of Cl, Br and I implies similar Cl/Br ( 160) and Br/I ( 90) in initial melts, volcanic clasts and high temperature gases. The low Cl/Br at SHV compared to other island arcs ( 250–300) is attributed to a shallow, pre-eruptive Br enrichment. The almost permanent dome extrusion at SHV since 1995 has likely had a significant regional atmospheric impact because of the very efficient effusive degassing and the high conversion rate of halogens into reactive species within the gas plume.     

The genesis of the carbonatized and silicified ultramafics known as listvenites: a case study from the Mihalıççık region (Eskişehir), NW Turkey

The Mihalıççık region (Eskişehir) in NW Turkey includes an ophiolitic assemblage with a serpentinite‐matrix mélange. The serpentinites of this mélange host silica‐carbonate metasomatites which were previously named as listvenites. Our mineralogical and geochemical studies revealed that these alteration assemblages represent members of the listvenitic series, mainly the carbonate rocks, silica‐carbonate rocks and birbirites, rather than true listvenites (sensu stricto). Tectonic activity and lithology are principal factors that control the formation of these assemblages. Carbonatization and silicification of the serpentinite host‐rock is generated by CO₂, SiO₂‐rich H₂O hydrothermal fluid which includes As, Ba, Sb and Sr. Low precious metal (Au, Ag) contents of the alteration assemblages indicate lack of these metals in the fluid. Primary assemblages of the alteration are carbonate rocks that are followed by silica‐carbonate rocks and birbirites, respectively. Petrographic studies and chemical analyses suggested an alkaline and moderate to high temperature (350–400°C) fluid with low oxygen and sulphur fugacity for the carbonatization of the serpentinites. The low temperature phases observed in the subsequent silicification indicated that the fluid cooled during progressive alteration. The increasing Fe‐oxide content and sulphur phases also suggested increasing oxygen and sulphur fugacity during this secondary process and silica‐carbonate rock formation. The occurrence of birbirites is considered as a result of reactivation of tectonic features. These rocks are classified in two sub‐groups; the Group 1 birbirites show analogous rare earth element (REE) trends with the serpentinite host‐rock, and the Group 2 birbirites simulate the REE trends of the nearby tectonic granitoid slices. The unorthodox REE trend of Group 2 birbirites is interpreted to have resulted from a mobilization process triggered by the weathering solutions rather than being products of enrichment by the higher temperature hydrothermal activity. Copyright © 2006 John Wiley & Sons, Ltd.     

The non‐trivial problem of meteorite pairing

Abstract— Pairing is the procedure of identifying fragments of a single meteorite fall (that were separated during atmospheric passage or during terrestrial history) by establishing the similarity of two or more meteorite fragments. We argue that pairing is governed by two principles, that only a single mismatch of properties is required to refute a proposed pairing, and that virtually all pairings bear some degree of uncertainty. Using data distributions for modern falls, we take a probability approach to estimate degrees of certainty associated with proposed pairings, emphasizing the importance of unusual features. For new pairing criteria or new analytical additions to old criteria, the degree of variation within individual meteorites must be delineated and the degree of variation within meteorite classes must be quantified. Criteria for pairing can be divided into (1) parent body history indicators, (2) meteoroid space history indicators, and (3) terrestrial history indicators. Included in these categories are 11 specific criteria, including petrographic textures, mineralogy and mineral composition, terrestrial age estimates, cosmic‐ray exposure ages, and natural thermoluminescence (TL) levels. Not all criteria are applicable to all meteorite types. About 2275 pairings suggested in the literature have been subjected to this analysis. Many literature pairings, especially those involving common meteorite types, bear large uncertainties due to lack of data.     

Using soil and Quaternary geological information to assess the intrinsic groundwater vulnerability of shallow aquifers: an example from Lithuania

Lithuania, in the Baltic region of northern Europe, is heavily dependent on groundwater resources for its public water supply, with a large proportion, especially in rural areas, derived from shallow Quaternary aquifers. A national groundwater-vulnerability methodology, based upon the UK approach, has been developed on behalf of the Lithuanian Ministry of Environmental Protection as a possible basis for the future protection of shallow groundwater resources for the rural inhabitants. Some modifications to the UK methodology were required to enable archive data to be used. The four aquifer classes depicted on the final groundwater vulnerability map are based upon the assessed relative permeabilities of the uppermost Quaternary deposits. The derivation of the classification of soil-leaching potential required a reassessment of Soviet-based soil wetness and particle-size classes and a calculation of subsoil-saturated hydraulic conductivity. A preliminary validation of the final maps against available shallow groundwater samples suggests that the methodology satisfactorily predicts the intrinsic groundwater vulnerability. The final methodology, based upon its low-cost approach using archive data, is relevant to the current needs of Lithuania and can be applied in other regions of similar geology and climate. Electronic Publication     

Scales of columnar jointing in igneous rocks: field measurements and controlling factors

Columnar jointing is a common feature of solidified lavas, sills and dikes, but the factors controlling the characteristic stoutness of columns remain debated, and quantitative field observations are few in number. In this paper, we provide quantitative measurements on sizing of columnar joint sets and our assessment of the principal factors controlling it. We focus on (1) chemistry, as it is the major determinant of the physical (mechanical and thermal) properties of the lava, and (2) geology, as it influences the style of emplacement and lava geometry, setting boundary conditions for the cooling process and the rate of heat loss. In our analysis, we cover lavas with a broad range of chemical compositions (from basanite to phonolite, for six of which we provide new geochemical analyses) and of geological settings. Our field measurements cover 50 columnar jointing sites in three countries. We provide reliable, manually digitized data on the size of individual columns and focus the mathematical analysis on their geometry (23,889 data on side length, of which 17,312 are from full column sections and 3,033 data on cross-sectional area and order of polygonality). The geometrical observations show that the variation in characteristic size of columns between different sites exceeds one order of magnitude (side length ranging from 8 to 338 cm) and that the column-bounding polygons’ average order is less than 6. The network of fractures is found to be longer than required by a minimum-energy hexagonal configuration, indicating a non-equilibrium, geologically quick process. In terms of the development and characteristic sizing of columnar joint sets, our observations suggest that columns are the result of an interplay between the geological setting of emplacement and magma chemistry. When the geological setting constrains the geometry of the emplaced body, it exerts a stronger control on characteristic column stoutness. At unconstrained geometries (e.g. unconfined lava flows), chemistry plays the major role, resulting in stouter columns in felsic lavas and slenderer columns in mafic lavas.     

Amount and type of derelict gear from the declining black pearl oyster aquaculture in Ahe atoll lagoon,French Polynesia

Pearl oyster aquaculture is a major activity in French Polynesia atoll lagoons. After the economic decline that characterized the last decade, concerns recently rose about discarded installations and materials that supported aquaculture practices and by facilities abandoned after they had to close their activities. In May 2013, a first inventory of the type and amount of pearl farms derelict gear (PFDG) was achieved on 47 sites in Ahe lagoon. Surveys were conducted within and outside the boundaries of aquaculture concessions. Twenty types of PFDG littered the lagoon floor and the water column. The most impacted areas were near abandoned grafting houses with up to nine types of PFDG. Forty-five percent of the sites were impacted, including outside concessions. While management authorities are fully aware of the problem, this first assessment is a wake-up call to stimulate the cleaning of lagoons, enhance awareness among farmers, and identify potential ecological consequences on lagoon ecosystems.     

Assessing impacts of invasive phytoplankton: The Baltic Sea case

There is an increasing understanding and requirement to take into account the effects of invasive alien species (IAS) in environmental quality assessments. While IAS are listed amongst the most important factors threatening marine biodiversity, information on their impacts remains unquantified, especially for phytoplankton species. This study attempts to assess the impacts of invasive alien phytoplankton in the Baltic Sea during 1980-2008. A bioinvasion impact assessment method (BPL - biopollution level index) was applied to phytoplankton monitoring data collected from eleven sub-regions of the Baltic Sea. BPL takes into account abundance and distribution range of an alien species and the magnitude of the impact on native communities, habitats and ecosystem functioning. Of the 12 alien/cryptogenic phytoplankton species recorded in the Baltic Sea only one (the dinoflagellate Prorocentrum minimum) was categorized as an IAS, causing a recognizable environmental effect.     

Monitoring vertical deformation due to water pumping in the city of Paris (France) with differential interferometry

The Saint-Lazare area in Paris (France) has undergone important water pumping for the construction of the underground Haussmann–Saint-Lazare station for the EOLE subway line. This paper presents the monitoring of the small surface displacements related to this pumping activity, by classical SAR interferometry. Piezometric measurements provided on 87 piezometers by SNCF and IGC as well as precise levelling data acquired on 626 points by SNCF are also examined. Their comparison with interferometric results shows their good agreement and complementarity, as well as the potential ‘operationality’ of SAR interferometric approach in such a study. To cite this article: B. Fruneau et al., C. R. Geoscience 337 (2005).