Oxygen isotopic signature of the skeletal microstructures in cultured corals: Identification of vital effects

In order to identify vital effect on oxygen isotopic ratio, we analyzed at micrometer size scale skeleton microstructures of a scleractinian coral Acropora, cultured under constant conditions. Measurements focused on the two crystalline units highlighted different isotopic signatures. Massive crystals (centers of calcification: COC) exhibit quasi-constant lowest values whereas fibers, the dominant units exhibit scattered distribution with amplitude of up to 5‰. Fiber oxygen isotopic ratios (δ¹⁸O) range from values similar to instantaneous deposition to equilibrium value. By comparing data obtained on the Acropora specimen and deep-sea corals grown under well constrained conditions, we infer that the scattered δ¹⁸O aragonite fibers indicate precipitation through kinetic precipitation. Thus, we argue for inherent biological feature typical to all coral genera. Modalities of COC formation remain ignored.The different isotopic signature of two mineral microstructures present in close proximity in coral skeleton can only be explained by compartment depositions related to different organic environments. Indeed, multiple secondary electron microscopy (SEM) observations favor interaction between mineral and organic matrix surface. Moreover, atomic forcing microscopy (AFM) investigations demonstrated thermodynamic changes induced by mineralization in presence of organic compounds. The combination of our results with previous published ones from biological studies, allows us proposing a consistent model of fiber skeleton formation. The prerequisite step of mineral growth unit precipitation would be initiated by organic matrix secretion, which defines spatial extension. Specific carriers supply ionic compounds of the crystals to ensure local supersaturation. However, possibly controlled by organic molecules, ionic amount would be limited, implying the supersaturation decline over the time. This could explain the progressive decrease of the coral growth rate. In this case, vital effect should not only bias isotopic fractionation through biological activity but the mechanism of skeleton deposition is imposed by specific chemical and/or physical conditions due to the presence of organic molecules. These conclusions derive from observations performed at high resolution.Therefore, isotopic ratio measured on millimeter scale for paleoclimatic purposes, result of the average of strongly heterogeneous values. It could explain vital effects shown by geochemical time series derived from tropical coral skeleton, including the high species and/or colony variability.     

Hydrogeological model of a high-energy geothermal field (Bouillante area, Guadeloupe, French West Indies)

The Bouillante geothermal field provides about 8% of the annual electricity needs of the French West Indies island of Guadeloupe. It has been the subject of several studies covering various disciplines. A hydrogeological conceptual model of the field is proposed. The reservoir consists of two perpendicular sets of fractures and faults, related to major regional tectonic structures, which have been clogged near surface by self sealing. The heat exchanges of the reservoir with the outside are reduced, through thermal and hydraulic blanketing, to conductive transfers. Convection cells are active within the reservoir, ensuring its thermal and geochemical homogeneity. Heat exchange with the magmatic chamber is only conductive. The Na–Cl geothermal fluid in the reservoir is composed of 60% seawater and 40% freshwater and has reached a chemical equilibrium with a mineralogical assemblage at 250–260°C. Many arguments (equilibrium state, absence of tritium, low in/out fluxes, large reservoir volume) suggest a long residence time (>100 years) of the geothermal fluid. Three factors explain the existence and location of the geothermal field: a heat source (cooling hypovolcanic intrusion), a network of permeable fractures at the origin of the geothermal aquifer, and an impermeable surface cover, limiting the loss of energy and ensuring the durability of the field.     

Volcano monitoring in NZ and links to SW Pacific via the Wellington VAAC

Monitoring for natural hazards like earthquakes, volcanic eruptions and landslides in New Zealand is under taken by GNS Science through the GeoNet project, funded by the Earthquake Commission (EQC). The volcano monitoring function, which includes seismograph and GPS networks, visual observations, webcams, deformation, gas and chemical measurements, assesses the status of New Zealand’s 12 active volcanoes and disseminates warnings as necessary. Interaction with the Wellington VAAC addresses aviation concerns. Near-real-time data is obtained from the monitoring networks and processed via two data centres, with two Duty Officers who respond to pager alerts. Through the National Civil Defence Plan, the volcano monitoring function is delegated to GNS Science, which is responsible for setting the volcanic alert level at each volcano. The Alert level is then used by responding agencies, industries, utility providers and the public to set their response. The New Zealand alert level system is based on the current status of the volcano, and is not necessarily predictive. The aviation industry is one of these responding industries. As a consequence of the 1995 and 1996 eruptions of Ruapehu volcano, it became apparent that the aviation industry required more information than the standard VAAC data and an additional service known as VAAS (NZ Volcanic Ash Advisory System) was established by MetService NZ and GNS Science. This arrangement provides enhanced services to the airlines and ensures rapid dissemination and quantification of information like SIGMET and NOTAM. GNS Science has informal relationships with similar geological based organisations in SW Pacific countries, especially Vanuatu and the Solomon Islands, and is able to quantify information about eruptions in those countries. Similarly, MetService NZ has relationships and is able to obtain pilot reports and updates from the meteorological and air traffic control organisations.     

Electron microbeam analysis of urban road-deposited sediment,Manchester, UK: Improved source discrimination and metal speciation assessment

Road-deposited sediment (RDS) is an accumulation of particulates upon street surfaces in urban centres. It is commonly highly contaminated and has major potential impacts upon surface water quality and human health, as well as becoming a waste material upon street sweeping. Although significant research has been undertaken upon the fine fraction within these systems, there is a lack of detailed, high-resolution grain-specific mineralogical and chemical data for the coarser fractions, which contain the bulk of the contamination by mass. The study reported here utilizes backscatter electron microscopic, electron microprobe and Raman spectroscopic analysis to provide novel data on RDS material from Manchester, UK, with significant implications for the improved understanding of source discrimination and contaminant metal speciation. The RDS samples studied are highly heterogeneous and the abundant nature of anthropogenic grains is particularly apparent. The RDS material has been found to be composed of a number of grain types: (i) silicate and alumino-silicate grains derived from a wide range of sources; (ii) iron oxide grains derived from the corrosion of galvanized steel; (iii) iron-rich glass grains derived as slag material from metal and waste processing activities and (iv) spherical Fe oxide and Fe-rich glass grains derived from high temperature combustion processes. Elemental metallic grains (Fe, Cu, Pb) are also present in minor amounts.     

Neoproterozoic to Early Cambrian history of an active plate margin in the Teplá–Barrandian unit—a correlation of U–Pb isotopic-dilution-TIMS ages (Bohemia, Czech Republic)

The Teplá–Barrandian unit (TBU) of the Bohemian Massif shared a common geological history throughout the Neoproterozoic and Cambrian with the Avalonian–Cadomian terranes. The Neoproterozoic evolution of an active plate margin in the Teplá–Barrandian is similar to Avalonian rocks in Newfoundland, whereas the Cambrian transtension and related calc-alkaline plutons are reminiscent of the Cadomian Ossa–Morena Zone and the Armorican Massif in western Europe. The Neoproterozoic evolution of the Teplá–Barrandian unit fits well with that of the Lausitz area (Saxothuringian unit), but is significantly distinct from the history of the Moravo–Silesian unit.The oldest volcanic activity in the Bohemian Massif is dated at 609+17/−19 Ma (U–Pb upper intercept). Subduction-related volcanic rocks have been dated from 585±7 to 568±3 Ma (lower intercept, rhyolite boulders), which pre-dates the age of sedimentation of the Cadomian flysch ( t chovice Group). Accretion, uplift and erosion of the volcanic arc is documented by the Neoproterozoic Dob í conglomerate of the upper part of the flysch. The intrusion age of 541+7/−8 Ma from the Zgorzelec granodiorite is interpreted as a minimum age of the Neoproterozoic sequence. The Neoproterozoic crust was tilted and subsequently early Cambrian intrusions dated at 522±2 Ma (T ovice granite), 524±3 Ma (V epadly granodiorite), 523±3 Ma (Smr ovice tonalite), 523±1 Ma (Smr ovice gabbro) and 524±0.8 Ma (Orlovice gabbro) were emplaced into transtensive shear zones.     

Cordieritite and Leucogranite Formation during Emplacement of Highly Peraluminous Magma: the El Pilon Granite Complex (Sierras Pampeanas, Argentina)

Cordieritites and highly peraluminous granites within the ElPilón granite complex, Sierras Pampeanas, Argentina,were emplaced during a medium-P, high-T metamorphic event duringthe initial decompression of a Cambrian orogen along the southwesternmargin of Gondwana. Very fresh orbicular and massive cordierititebodies with up to 90% cordieritite are genetically associatedwith a cordierite monzogranite pluton and a larger body of porphyriticgranodiorite. The petrogenesis of this association has beenstudied using petrographical, mineralogical, thermobarometric,geochemical, geochronological and isotope methods. The graniticmagmas were formed by anatexis of mid-crustal metamorphic rocksformed earlier in the Pampean orogeny. The cordieritites appearat the top of feeder conduits that connected the source regionlocated at     

Cu–Fe Bearing Zinc Sulfide from Laloki Stratabound Massive Sulfide Deposit, Papua New Guinea: Chemical Characterization

Abstract: A strange, unidentified, Cu-Fe bearing zinc sulfide occurs in the Laloki massive sulfide deposit, Papua New Guinea. The mineral is optically uniform in texture but is chemically variable and zoned even within a single grain. Copper contents vary from 0.1 up to 8.85 wt%. Iron reaches 18.31 wt% at maximum and decreases as Cu increases. It is remarkable, however, that the total Fe+Cu remains essentially unchanged between roughly 18 and 20 wt%. Zn and S are least variable, giving 45.85–47.84 wt% and 33.48–34.58 wt%, respectively. Other trace elements such as Cd and Mn are in general less than 0.2 wt%. It is strongly suggested that the mineral in question constitutes a unique Fe-Cu substitutional solid solution series belonging essentially to the Zn–Fe–Cu–S system.
The ideal chemical formula of the solid solution series can well be presented as Zn₁₀(Fe, Cu)₅S₁₅ or Zn₂(Fe, Cu)S₃, where Fe is always greater than Cu. It is intriguing that chalcopyrite blebs are recognizable restrictively only in nearby portions of the Cu-rich end member with the ideal composition close to Zn₁₀Fe₃Cu₂S_15. It has been confirmed by vacuum-sealed heating experiments that this mineral is decomposed to produce chalcopyrite and Fe-bearing normal sphalerite at temperatures below 200C. This would provide another evidence for the existence of such distinct phase as suggested here.     

Paleozoic Accretion-Collision Events and Kinematics of Ductile Deformation in the Eastern Part of the Southern-Central Tianshan Belt, China

The Tianshan range could have been built by both late Early Paleozoic accretion and Late Paleozoic collision events. The late Early Paleozoic Aqqikkudug-Weiya suture is marked by Ordovician ophiolitic melange and a Silurian flysch sequence, high-pressure metamorphic relics, and mylonitized rocks. The Central Tianshan belt could principally be an Ordovician volcanic arc; whereas the South Tianshan belt, a back-arc basin. Macro- and microstructures, along with unconformities, provide some kinematic and chronological constraints on 2-phase ductile deformation. The earlier ductile deformation occurring at ca. 400 Ma was marked by north-verging ductile shearing, yielding granulite-bearing ophiolitic melange blocks and garnet-pyroxene-facies ductile deformation, and the later deformation, a dextral strike-slip tectonic process, occurred during the Late Carboniferous-Early Permian. Early Carboniferous molasses were deposited unconformably on pre-Carboniferous metamorphic and ductilely sheared rocks, implying t     

Formation of metal in Grosvenor Mountains 95551 and comparison to ordinary chondrites

Siderophile element abundances in individual metal grains in the ungrouped chondrite Grosvenor Mountains (GRO) 95551 and in the ordinary chondrites Tieschitz H3.6, Soko-Banja LL4, and Allegan H5 were measured with laser ablation-inductively coupled plasma mass spectrometry. Matrix metal in GRO 95551 falls into two distinct compositional groups, a high-Ni group with 7.2 ± 0.4 wt% Ni and a low-Ni group with 3.7 ± 0.1 wt% Ni, indicating that kamacite/taenite equilibration at ∼1020 K was followed by rapid cooling. The nonrefractory siderophile elements P, Co, Cu, Ga, Ge, As, Pd, and Au also partition between the high-Ni and low-Ni metal in a manner consistent with kamacite/taenite fractionation, but the refractory siderophiles Ru, Re, Os, Ir, and Pt show correlated variations that are unrelated to kamacite/taenite partitioning and indicate that variations in refractory components of the metal were not completely erased during equilibration at ∼1020 K. The Ni-normalized bulk metal composition of GRO 95551 is refractory depleted and volatile rich relative to Bencubbin and related metal-rich chondrites but bears strong similarities to equilibrated ordinary chondrite metal. GRO 95551 represents a new chondrite type with chemical affinity to the ordinary chondrites. Individual metal grains in unequlibrated ordinary chondrites also have correlated variations in refractory siderophile contents that cannot be produced by redox processes alone; these variations span three orders of magnitude and diminish with increasing metamorphic grade of the ordinary chondrites.