Carbonic inclusions

The paper gives an overview of the phase relations in carbonic fluid inclusions with pure, binary and ternary mixtures of the system CO₂–CH₄–N₂, compositions, which are frequently found in geological materials. Phase transitions involving liquid, gas and solid phases in the temperature range between −192°C and 31°C are discussed and presented in phase diagrams (PT, TX and VX projections). These diagrams can be applied for the interpretation of microthermometry data in order to determine fluid composition and molar volume (or density).     

Dating emplacement and evolution of the orogenic magmatism in the internal Western Alps: 2. The Biella Volcanic Suite

The high-pressure metamorphic rocks of the Sesia?CLanzo zone are partly covered by a volcano-sedimentary unit, the Biella Volcanic Suite. Calc-alkaline and shoshonitic lavas extruded sub-aerially on the Oligocene surface. Uranium?CLead zircon dating yields 32.44?C32.89?Ma for the eruption of the calc-alkaline lavas and therefore fixes a minimum age for the paleosurface. The Biella Volcanic Suite consists mainly of epiclastic rocks deposited in a high-energy fluvial environment and minor lava flows. The rocks of the suite display widespread post-eruption transformations. Illite and chlorite thermometry as well as fission track dating suggest a thermal overprint related to burial of the Biella Volcanic Suite. An upper crustal rigid block tilting in the area causes this burial. Hydrothermal tourmaline and ankerite veins related to the intrusion of the nearby Valle del Cervo Pluton crosscut the already tilted Biella Volcanic Suite. The intrusion age of Valle del Cervo Pluton at 30.39?±?0.50?Ma sets therefore the lower time limit for tectonic processes responsible for the tilting and burial. After the burial, the Biella Volcanic Suite remained for around 20?million years between the zircon and the apatite partial annealing zone. The apatite fission track ages spread between 16 and 20?Ma gives the time frame for the second exhumation of these units. The Biella Volcanic Suite and the adjacent rocks of the Sesia?CLanzo zone were the second time exhumed to the surface in Messinian times, after a long residence time within the apatite partial annealing zone.     

Analysis of farm performance in Europe under different climatic and management conditions to improve understanding of adaptive capacity

The aim of this paper is to improve understanding of the adaptive capacity of European agriculture to climate change. Extensive data on farm characteristics of individual farms from the Farm Accountancy Data Network (FADN) have been combined with climatic and socio-economic data to analyze the influence of climate and management on crop yields and income and to identify factors that determine adaptive capacity. A multilevel analysis was performed to account for regional differences in the studied relationships. Our results suggest that socio-economic conditions and farm characteristics should be considered when analyzing effects of climate conditions on farm yields and income. Next to climate, input intensity, economic size and the type of land use were identified as important factors influencing spatial variability in crop yields and income. Generally, crop yields and income are increasing with farm size and farm intensity. However, effects differed among crops and high crop yields were not always related to high incomes, suggesting that impacts of climate and management differ by impact variable. As farm characteristics influence climate impacts on crop yields and income, they are good indicators of adaptive capacity at farm level and should be considered in impact assessment models. Different farm types with different management strategies will adapt differently.     

Symposium über Fragen der Cyanophytentaxonomie in Kastanienbaum, 3.–16. August 1972

Ohne Zusammenfassung Internationale Arbeitsgemeinschaft für Cyanophytenforschung IAC     

Zur Systematik derChroococcaceae

Ohne Zusammenfassung     

The effect of deformation on the TitaniQ geothermobarometer: an experimental study

We performed high strain (up to 47 %) axial compression experiments on natural quartz single crystals with added rutile powder (TiO₂) and ~0.2 wt% H₂O to investigate the effects of deformation on the titanium-in-quartz (TitaniQ) geothermobarometer. One of the objectives was to study the relationships between different deformation mechanisms and incorporation of Ti into recrystallized quartz grains. Experiments were performed in a Griggs-type solid-medium deformation apparatus at confining pressures of 1.0–1.5 GPa and temperatures of 800–1,000 °C, at constant strain rates of 1 × 10^?6 or 1 × 10^?7 s^?1. Mobility of Ti in the fluid phase and saturation of rutile at grain boundaries during the deformation experiments are indicated by precipitation of secondary rutile in cracks and along the grain boundaries of newly recrystallized quartz grains. Microstructural analysis by light and scanning electron microscopy (the latter including electron backscatter diffraction mapping of grain misorientations) shows that the strongly deformed quartz single crystals contain a wide variety of deformation microstructures and shows evidence for subgrain rotation (SGR) and grain boundary migration recrystallization (GBMR). In addition, substantial grain growth occurred in annealing experiments after deformation. The GBMR and grain growth are evidence of moving grain boundaries, a microstructure favored by high temperatures. Electron microprobe analysis shows no significant increase in Ti content in recrystallized quartz grains formed by SGR or by GBMR, nor in grains grown by annealing. This result indicates that neither SGR nor moving grain boundaries during GBMR and grain growth are adequate processes to facilitate re-equilibration of the Ti content in experimentally deformed quartz crystals at the investigated conditions. More generally, our results suggest that exchange of Ti in quartz at low H₂O contents (which may be realistic for natural deformation conditions) is still not fully understood. Thus, the application of the TitaniQ geothermobarometer to deformed metamorphic rocks at low fluid contents may not be as straightforward as previously thought and requires further research.     

Internal Differentiation of the Archean Continental Crust: Fluid-Controlled Partial Melting of Granulites and TTG-Amphibolite Associations in Central Finland

Fault bound blocks of granulite and enderbite occur within upperamphibolite-facies migmatitic tonalitic–trondhjemitic–granodioritic(TTG) gneisses of the Iisalmi block of Central Finland. Theseunits record reworking and partial melting of different levelsof the Archean crust during a major tectonothermal event at2·6–2·7 Ga. Anhydrous mineral assemblagesand tonalitic melts in the granulites formed as a result ofhydrous phase breakdown melting reactions involving amphiboleat peak metamorphic conditions of 8–11 kbar and 750–900°C.A nominally fluid-absent melting regime in the granulites issupported by the presence of carbonic fluid inclusions. Thegeochemical signature of light rare earth element (LREE)-depletedmafic granulites can be modelled by 10–30 wt % partialmelting of an amphibolite source rock leaving a garnet-bearingresidue. The degree of melting in intermediate granulites isinferred to be less than 10 wt % and was restricted by the availabilityof quartz. Pressure–temperature estimates for the TTGgneisses are significantly lower than for the granulites at660–770°C and 5–6 kbar. Based on the P–Tconditions, melting of the TTG gneisses is inferred to haveoccurred at the wet solidus in the presence of an H₂O-rich fluid.A hydrous mineralogy, abundant aqueous fluid inclusions andthe absence of carbonic inclusions in the gneisses are in accordancewith a water-fluxed melting regime. Low REE contents and strongpositive Eu anomalies in most leucosomes irrespective of thehost rock composition suggest that the leucosomes are not meltcompositions, but represent plagioclase–quartz assemblagesthat crystallized early from felsic melts. Furthermore, similarplagioclase compositions in leucosomes and adjacent mesosomesare not a ‘migmatite paradox’, as both record equilibrationwith the same melt phase percolating along grain boundaries. KEY WORDS: Archean continental crust; fluid inclusion; granulite; migmatite; partial melting     

The composition and evolution of an Oligocene regolith on top of the Sesia–Lanzo Zone (Western Alps)

An Oligocene paleosurface (regolith) lies on top of the high-pressure metamorphic rocks of the Sesia–Lanzo Zone near Biella, NW Italy. Only the saprock, the lowermost part in a regolith profile, is preserved. No evidence for any paleosoil can be observed. Field observations indicate that the regolith developed through in situ mechanical fracturing of the rocks of the Sesia–Lanzo Zone in a continental environment. Density estimations of the regolith and the underlying rocks of the Sesia–Lanzo Zone confirm the field observations and imply that a relatively small amount of alteration minerals was formed. The main detected alteration phases are chlorite, various carbonates, quartz, clay minerals, Fe-oxides, and Fe-hydroxides. Chlorite differing in chemistry and crystallographic ordering demonstrates different stages of alteration. Oxygen and carbon isotopic composition of carbonates suggests temperatures higher than surface conditions. Illite and chlorite thermometry indicates temperatures related to the anchizone (~250–300°C). These data are considered as a robust indication of the re-burial of the regolith together with its substrate and its volcanic cover. The burial is closely related to the tilting of the preserved stratigraphic sequence formed by the rocks of the Sesia–Lanzo Zone, the regolith, and the rocks of the Biella Volcanic Suite (Lanza, in Schweiz Miner Petrogr MItt 57: 281–290, 1977; Lanza, in Geologishe Rundschau 68: 83–92, 1979). Furthermore, the burial is consistent with this sequence of subaerial rocks being very close to the intrusion depth of the Valle del Cervo Pluton at the time of its emplacement (4–7 km; Zanoni et al., in Rend Online SGI Note Brevi 1: 199–202, 2008; Zanoni et al., in Int Geol Rev 52: 1244–1267, 2010 and references therein).