Calcium isotope (δCa) fractionation along hydrothermal pathways, Logatchev field (Mid-Atlantic Ridge, 14°45′N)

We investigate the Logatchev Hydrothermal Field at the Mid-Atlantic Ridge, 14°45′N to constrain the calcium isotope hydrothermal flux into the ocean. During the transformation of seawater to a hydrothermal solution, the Ca concentration of pristine seawater ([Ca]_SW) increases from about 10 mM to about 32 mM in the hydrothermal fluid endmember ([Ca]_HydEnd) and thereby adopts a δ^44/40Ca_HydEnd of −0.95 ± 0.07‰ relative to seawater (SW) and a ⁸⁷Sr/⁸⁶Sr isotope ratio of 0.7034(4). We demonstrate that δ^44/40Ca_HydEnd is higher than that of the bedrock at the Logatchev field. From mass balance calculations, we deduce a δ^44/40Ca of −1.17 ± 0.04‰ (SW) for the host-rocks in the reaction zone and −1.45 ± 0.05‰ (SW) for the isotopic composition of the entire hydrothermal cell of the Logatchev field. The values are isotopically lighter than the currently assumed δ^44/40Ca for Bulk Earth of −0.92 ± 0.18‰ (SW) [Skulan J., DePaolo D. J. and Owens T. L. (1997) Biological control of calcium isotopic abundances in the global calcium cycle. Geochim. Cosmochim. Acta61,(12) 2505-2510] and challenge previous assumptions of no Ca isotope fractionation between hydrothermal fluid and the oceanic crust [Zhu P. and Macdougall J. D. (1998) Calcium isotopes in the marine environment and the oceanic calcium cycle. Geochim. Cosmochim. Acta62,(10) 1691-1698; Schmitt A. -D., Chabeaux F. and Stille P. (2003) The calcium riverine and hydrothermal isotopic fluxes and the oceanic calcium mass balance. Earth Planet. Sci. Lett. 6731, 1-16]. Here we propose that Ca isotope fractionation along the fluid flow pathway of the Logatchev field occurs during the precipitation of anhydrite. Two anhydrite samples from the Logatchev Hydrothermal Field show an average fractionation of about Δ^44/40Ca = −0.5‰ relative to their assumed parental solutions. Ca isotope ratios in aragonites from carbonate veins from ODP drill cores indicate aragonite precipitation directly from seawater at low temperatures with an average δ^44/40Ca of −1.54 ± 0.08‰ (SW). The relatively large fractionation between the aragonite precipitates and seawater in combination with their frequent abundance in weathered mafic and ultramafic rocks suggest a reconsideration of the marine Ca isotope budget, in particular with regard to ocean crust alteration.     

Geophysiology and Parahistology of the Interactions of Organisms with the Environment*

Abstract. Ecology and Global Ecology (GE) are terms by which the relations between the organism (or living matter as a whole) and the environment (or Earth as a whole) have been treated for almost a century. Geophysiology and Parahistology (PH) are terms slowly replacing older scientific thoughts jointly with an increasing number of modifications and alterations of the Darwinian Evolution (DE) concept. Somehow Geophysiology and Parahistology seem to describe evolution in a non-Darwinian domain. According to V.I. Vernadsky (1929,1930,1988) - the great Russian naturalist and biogeochemist - the biogeochemical processes on Earth are controlled by the force of living matter rather than by species associations developing in and with individual ecosystems as expressed by darwinian evolutionary terms. He also claimed that Goethe was incorrectly regarded as a predecessor of DE by some authors (including Darwin) and that “Natur” (nature) and “Lebendige Natur” (the totality of creatures) are two very different things for Goethe. Detailed analyses of microbial mat systems in the German Wadden Sea and in artificial hypersaline WInogradsky columns have shown that the totality of creatures and matter around them i.e., the “lebendige Natur”sensu Goethe or “living matter”sensu Vernadsky of such environments control to a considerable extent the structure, stability. and (geo-)morphology of sediments and thereby the geological structure of the living Earth. These structures do not follow the rules of sedimentation formulated by the laws of Stokes They represent growth structures (Aufwuchs), whose physics and dynamics are controlled by complex fractal systems. The factors controlling the ultimate shape and stabilisation potential of the eventually resulting rocks and fossils are comparable to tissue development in macroorganisms. Also, certain microbial associations in the sub-recent and in the fossil record may be compared to metazoan tissues. Chemical gradients in the sedimentary column, regulated by the interplay of living matter and sluggish (slow-reactive to non-reactive) compounds, combine to create a pattern of porosity and structure of the resulting deposits that clearly indicates microbial influences and especially those of extracellular polymeric substances on the morphology and texture. The combined effects of microbiota or living matter on the sedimentary record are described as parahistology of sediments in analogy of the histology of tissue on a geological scale. This conceptual living tissue made up of microbially generated rocks and ore deposits cycled through metabolic processes and forced into tissue-like structures by microbial biofilms and mats may extend down to the upper mantle of Earth and far up into the stratosphere when Earth is regarded as a living entity over geological periods. We may have to conceive Earth as a living specimen, which is breathing at a frequency of thousands of years instead of the normal physiological breathing rate of man or an insect. Macroorganisms in all terrestrial systems represent the transport and logistic media, which, however, utterly depend on myriads of intra-, inter-, and extracellular microbial symbiotic partners.     

The eastern continuation of the Cadomian orogen: U–Pb zircon evidence from Saxo-Thuringian granitoids in south-western Poland and the northern Czech Republic

We report U–Pb single zircon ages from three pre-Variscan granitoids in the NE part of the Bohemian Massif. The Platerówka granodiorite from the Lausitz-Izera Unit, the Polish Sudetes, has been dated at 533±9 Ma. The Bitouchov granite form the SW part of the South Krkonoe Unit, the Czech Sudetes, gave an age of 540+11/–10 Ma, and the Wdroe granodiorite in the Fore-Sudetic Block yielded 548±9 Ma. All these latest Vendian/Early Cambrian granitoids represent the post-tectonic expression of a late Proterozoic Cadomian orogenic cycle and demonstrate the eastward extent of the Cadomian basement into the Variscan orogen. Granodiorites of similar age have so far been reported from Brittany and especially from the Saxo-Thuringian Terrane to the NE and SW of the Elbe Fault Zone. We conclude that the Saxo-Thuringian Terrane extends across the Elbe and Sudetic Marginal Fault Zones into the Fore-Sudetic Block.     

Zum System der Meeresströmungen in den höheren Breiten

Zusammenfassung Es wird gezeigt, daß in den höheren Breiten zwischen dem ozeanischen Stromfeld und der Windverteilung beträchtliche Unterschiede bestehen. Daher wird als Ursache des Strömungssystems nicht das Windfeld, sondern die Süßwasserzufuhr vom Festland angesehen, welche als Salzgehaltsstörung das küstennahe Massenfeld beherrscht und entsprechend dem Theorem nach Bjerknes ein Gradientstromsystem bedingt, welches dem beobachteten entspricht.

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A contribution to the system of ocean currents in the higher latitudes

Summary It is demonstrated that in the high latitudes, considerable differences exist between the oceanic current system and the wind distribution. It is, therefore, supposed that it is not the windfield that gives rise to the existing current system but the supply of fresh water from the continent which, as a salinity disturbance, plays a dominant part in the field of mass near the coast. According to Bjerknes' theorem, the disturbance of salinity conditions a gradient current system; this is in good agreement with the observations.

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Sur le système de courants marins par les hautes latitudes

Résumé On montre qu'il existe par les hautes latitudes de différences considérables entre le système de courants océaniques et la distribution des vents. Pour cette raison, on suppose que c'est l'afflux d'eau douce venant du continent et non le champ du vent qui engendre le système de courants dominant, sous la forme d'une perturbation de salinité, le champ de masse près des côtes. D'après le théorème de Bjerknes le système de courants de gradient est la conséquence nécessaire de la perturbation de salinité ce qui est en bon accord avec les observations faites dans ce domaine.

     

Modelling of paleo-saltwater intrusion in the northern part of the Nubian Aquifer System, Northeast Africa

A numerical groundwater model of the Nubian Aquifer System was established to prove the influence of rising seawater levels on the groundwater salinity in northern Egypt over the last 140,000 years. In addition, the impact of a groundwater recharge scenario for these 140,000 years, involving climatic change, on the saltwater/freshwater interface was investigated. Saltwater intrusion induced by rising water levels of the Mediterranean Sea led to salinisation from the Mediterranean Sea to the Qattara depression. This modeling approach was supported by a density-driven model setup and calculation. The modelled saltwater/freshwater interfaces partially fitted the observed ones, especially in the southern half of the Qattara depression. In other parts of the northern Nubian Aquifer System, the ingression of salt water was modelled adequately, but in the west, small regions of the measured interface were not. The development in the Qattara depression (Egypt) and Sirte basin (Libya) were investigated in more detail. The different behaviour in the Sirte basin may be due to high evapotranspiration rates in some former periods, salt solutions from the pre-Quaternary layers or saltwater infiltration from sabkha-like recent salt-bearing sediments.     

The measurement of sulfate mineral solubilities in the Na-K-Ca-Cl-SO4-H2O system at temperatures of 100, 150 and 200°C

At T > 100°C development of thermodynamic models suffers from missing experimental data, particularly for solubilities of sulfate minerals in mixed solutions. Solubilities in Na⁺-K⁺-Ca²⁺-Cl⁻-SO₄²⁻/H₂O subsystems were investigated at 150, 200°C and at selected compositions at 100°C. The apparatus used to examine solid-liquid phase equilibria under hydrothermal conditions has been described.In the system NaCl-CaSO₄-H₂O the missing anhydrite (CaSO₄) solubilities at high NaCl concentrations up to halite saturation have been determined. In the system Na₂SO₄-CaSO₄-H₂O the observed glauberite (Na₂SO₄ · CaSO₄) solubility is higher than that predicted by the high temperature model of Greenberg and Møller (1989), especially at 200°C. At high salt concentrations, solubilities of both anhydrite and glauberite increase with increasing temperature. Stability fields of the minerals syngenite (K₂SO₄ · CaSO₄ · H₂O) and goergeyite (K₂SO₄ · 5 CaSO₄ · H₂O) were determined, and a new phase was found at 200°C in the K₂SO₄-CaSO₄-H₂O system. Chemical and single crystal structure analysis give the formula K₂SO₄ · CaSO₄. The structure is isostructural with palmierite (K₂SO₄ · PbSO₄). The glaserite (“3 K₂SO₄ · Na₂SO₄”) appears as solid solution in the system Na₂SO₄-K₂SO₄-H₂O. Its solubility and stoichiometry was determined as a function of solution composition.     

Seismic lamination and anisotropy of the Lower Continental Crust

Seismic lamination in the lower crust associated with marked anisotropy has been observed at various locations. Three of these locations were investigated by specially designed experiments in the near vertical and in the wide-angle range, that is the Urach and the Black Forrest area, both belonging to the Moldanubian, a collapsed Variscan terrane in southern Germany, and in the Donbas Basin, a rift inside the East European (Ukrainian) craton. In these three cases, a firm relationship between lower crust seismic lamination and anisotropy is found. There are more cases of lower-crustal lamination and anisotropy, e.g. from the Basin and Range province (western US) and from central Tibet, not revealed by seismic wide-angle measurements, but by teleseismic receiver function studies with a P–S conversion at the Moho. Other cases of lamination and anisotropy are from exhumed lower crustal rocks in Calabria (southern Italy), and Val Sesia and Val Strona (Ivrea area, Northern Italy). We demonstrate that rocks in the lower continental crust, apart from differing in composition, differ from the upper mantle both in terms of seismic lamination (observed in the near-vertical range) and in the type of anisotropy. Compared to upper mantle rocks exhibiting mainly orthorhombic symmetry, the symmetry of the rocks constituting the lower crust is either axial or orthorhombic and basically a result of preferred crystallographic orientation of major minerals (biotite, muscovite, hornblende). We argue that the generation of seismic lamination and anisotropy in the lower crust is a consequence of the same tectonic process, that is, ductile deformation in a warm and low-viscosity lower crust. This process takes place preferably in areas of extension. Heterogeneous rock units are formed that are generally felsic in composition, but that contain intercalations of mafic intrusions. The latter have acted as heat sources and provide the necessary seismic impedance contrasts. The observed seismic anisotropy is attributed to lattice preferred orientation (LPO) of major minerals, in particular of mica and hornblende, but also of olivine. A transversely isotropic symmetry system, such as expected for sub-horizontal layering, is found in only half of the field studies. Azimuthal anisotropy is encountered in the rest of the cases. This indicates differences in the horizontal components of tectonic strain, which finally give rise to differences in the evolution of the rock fabric.