North-south transfer zones and paleo-morphological reconstruction of the Xylokastro area (Corinth Gulf, Greece)

A large number of studies have documented the structural and sedimentary architecture of the Corinth Gulf, especially the major E–W trending normal faults important in accommodating the main extensional strain and associated growth of the Gilbert fan deltas. However, the role of several N–S oriented structures that crop out at the surface and are detectable at depth by seismic reflection and gravity surveys are not clearly understood. Based on new geological data, collected near Xylokastro, we describe the N–S oriented tectonic activity of this area. The mapped inland faults correspond to off-shore structures identified in re-interpreted seismic lines and appear to have acted as a major transfer zone during the opening of the Corinth Gulf. Reconstruction of the paleo-topography based on sedimentary facies and the environment of clay mineral formation suggest these transfer zones played an important role in controlling both local structural relief and depositional conditions of the Gilbert fan deltas.     

Correlation of δ<Superscript>18</Superscript>O and initial<Superscript>87</Superscript>Sr/<Superscript>86</Superscript>Sr ratios in Kirkpatrick basalt on Mt. Falla,transantarctic mountains

Theδ¹⁸O (SMOW) values of the Kirkpatrick Basalt (Jurassic) on Mt. Falla, Queen Alexandra Range, vary between +6.3‰ and +8.6‰ The apparent enrichment of these rocks in¹⁸O excludes the possibility that they were altered by interaction with aqueous solutions of meteoric origin. Theδ¹⁸O values of the flows correlate significantly with the initial⁸⁷Sr/⁸⁶Sr ratios and all major elements. These correlations confirm the hypothesis that the basalt magma was contaminated by rocks of the continental crust through which it was extruded. Estimates of the chemical composition of the basalt magma and the contaminant, based on extrapolations of the new oxygen data, generally confirm earlier estimates based on extrapolations of initial⁸⁷Sr/⁸⁶Sr ratios. The⁸⁷Sr/⁸⁶Sr ratio of the uncontaminated basalt was 0.7093 which indicates that magma may have originated by melting either in old Rb-enriched lithospheric mantle under Antarctica or in the overlying crust, or both.     

Kontinentalverschiebungen und Polverschiebungen — Ursachen und Probleme

Zusammenfassung Die Kruste wird zergliedert von einem Gitter altgebahnter Lineamente, welche immer wieder als Blattverschiebungen fungierten. Die gro\en Gräben Ostafrikas und Europas setzen solchen Erdnähten auf. Die starren Rahmenschollen waren etwas auseinander gewichen. So konnten die von der Kluftreibung befreiten Keilschollen rasch absinken, antithetisch kippende Blöcke den überschüssigen Scitenraum schlie\en. Junge Füllmassen wurden aufgeladen, welche die Erosion den aufgestemmten Grabenschultern entnahm. Das granitische Substrat solcher Gräben ist geschwächt, im Graben des Roten Meeres sogar median geborsten. Ein abyssaler Spalt mit basaltischem Sockel klafft dort inmitten des Altgrabens. Die Abspaltung Südamerikas vom Gondwana-Kontinent bediente sich gleichfalls alter Lineamente. Der Atlantik erweiterte sich aus einem Grabensystem. Der seismisch aktive Mediangraben des mittelatlantischen Rückens demonstriert den Fortgang der Kontinentaldrift. Auch andere Kontinente kriechen auf einer Gleitschichte pazifikwärts, die pazifische Masse mit einer überschiebungsbahn und Blattverschiebungen bewältigend. Der übereinstimmende Baustil zirkumpazifischer Tektonik beweist periphere Einengungen des Pazifik. Die gro\en Urkontinente störten das irdische Rotationsgleichgewicht. Daher die Tendenz, den Störkörper zu spalten und die Erdoberfläche möglichst gleichmä\ig mit Kontinenten zu bestücken. Als Rei\nähte boten sich die Gräben und Lineamente an, welche angelegt waren, die Scherspannungen auszugleichen, wenn Polverschiebungen das Rotationsellipsoid zur Neujustierung zwangen. Die abdriftenden Kontinente induzierten sekundäre Gleichgewichtsstörungen und erneute Polverschiebungen. Wieder wurden Scherzonen lebendig, Kontinentaldrift setzte an und erweiterte sie zu Gräben, um schlie\lich ein weiteres Stück Kruste der Klammer kontinentaler Konsolidation zu entrei\en. So werden Polverschiebungen und Kontinentalverschiebungen als einander auslösende und steuernde Prozesse verstanden. Das orogene ZeitgesetzStilles wird unter diesem Aspekt diskutiert.

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The crust of the earth is traversed by a lattice of tectonic lineaments which, since the Precambrian Era, were always and again acting as wrench faults. These shearing movements, independent of the specific crustal structure, are thought to be caused by the wandering of the poles. For the directions and movements of the lineaments correspond to the stress field that was induced by the readjustment of the geoid. The bursting lineaments caused a splitting of the continental masses. The great original continents of the Paleozoic Era disturbed the balance of revolution. There was a trend to separate the disturbing masses and to furnish the surface of the earth as proportionally as possible with continents. Thus, divergent forces started to work on the lineaments. The lineaments were stretched and became rift valleys. When the forces of the continental drift became overwhelming, the rift valleys burst along their median line. A new continent split off. The wandering continents endeavoured and are still endeavouring to reach, in the first place, the Pacific Ocean trying to confine it peripherically. From this trend comes the conformable architecture of the circumpacific tectonics. The drifting masses effected secondary disturbances of the balance of the rotating gyroscope. The poles tried to escape the wandering masses. Once more, lineaments became active, and the process of splitting continued. Consequently, the wandering of the poles and the continental drift are thought to be mutually initiating and controlling processes. The orogenic phases of the folding and the taphrogenic phases of the rift valley forming are in their global coincidence the display of this very process that concerns the entire crust of the earth.

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Résumé L'écorce terrestre est sillonnée d'un réseau de linéaments tectoniques, qui se remuaient à partir de temps précambriens et qui continuent de se remuer au sens de failles de décrochement. Les mouvements ne tiennent pas compte de la structure géologique de la région en question. On suppose que la cause des mouvements soit la dérive des pÔles, parceque les directions des linéaments tectoniques correspondent aux celles-ci de la tension de l'écorce provoquée par le ré-ajustage du géoid. En se fendant le longue des linéaments les masses des continents furent parcellées. - Les grands continents du Paléozoique dérangaient l'équilibre de la rotation. Cet dérangement causait la tendance de répartir les masses des continents et d'en garnir la surface du globe. Le longue des linéaments agissaient des forces séparentes. Les linéaments s'élargissaient et devenaient des fossés tectoniques. Si les forces de la dérive des continents se renforÇaient les fossés tectoniques se partagissaient le longue de ses médianes. Un nouveau continent était formé. Mises en translation les continents se tournaient vers la région de l'Océan Pacifique, et aussi à present les continents continuent de rétrecir la région marginale du Pacifique. C'est pourquoi le type de la construction tectonique est le mÊme dans toutes les guirlandes circumpacifiques. Les translations continentales causaient des dérangements secondaires de l'équilibre du géoid et les pÔles fuyaient les continents. De nouveau les linéaments tectoniques se remuaient et la division des continents se continuait. La dérive des pÔles et la dérive des continents sont des événements dont l'un provoque et dirige l'autre. L'expression de cet événement concernant l'écorce entière est la simultanéité des phases orogénétiques (plissement) et des phases taphrogéniques (formation des fossés tectoniques).

     

Central Europe: Active or residual tectonic stresses

The regional stress field in the Western Alps and their northern foreland has been investigated byin situ stress determinations. More than 600 strain relief measurements were made with resistance strain gages in boreholes carried out in mines, tunnels and quarries. The stresses calculated and data obtained from other papers were used to get a detailed idea of the stress conditions in Central Europe.The measurements confirm a continuous flux of compressive stress from the Alps to the northern foreland east of the Rhinegraben. The largest stresses are observed in the Central Alps, the lowest in the Rhinegraben rift system. The horizontal stresses exceed at nearly all places the vertical ones. Evidently the excess of horizontal stress is generated by active plate tectonics in the Alps. A tectonic model to explain the observed stress pattern is presented.     

δ13C signature of early graphite and subsequently formed microdiamond from the Saxonian Erzgebirge,Germany

Microdiamond and graphite occur in quartzofeldspathic rocks (saidenbachites) of the central Erzgebirge in Saxony. Zircon from such rocks contains not only relatively high but also variable amounts of early formed graphite and later crystallized diamond, however no carbonate. Six purified zircon concentrates were analysed by mass spectrometry for δ₁₃C(PDB) values which were between −24 and −33‰. The carbon inclusions resulted in C contents of the concentrates as high as 0.5 wt%. It is hypothesized that the observed δ₁₃C signature results from organic material in the sedimentary protoliths of the saidenbachites probably deposited not earlier than Mid‐Devonian. This material was transformed to graphite during early metamorphism and subsequently to diamond after an anatectic event at great depths (>150 km). During these processes, the δ₁₃C signature of the carbon did not (significantly) change.     

From planetesimals to terrestrial planets: N-body simulations including the effects of nebular gas and giant planets

We present results from a suite of N-body simulations that follow the formation and accretion history of the terrestrial planets using a new parallel treecode that we have developed. We initially place 2000 equal size planetesimals between 0.5 and 4.0 AU and the collisional growth is followed until the completion of planetary accretion (>100 Myr). A total of 64 simulations were carried out to explore sensitivity to the key parameters and initial conditions. All the important effect of gas in laminar disks are taken into account: the aerodynamic gas drag, the disk-planet interaction including Type I migration, and the global disk potential which causes inward migration of secular resonances as the gas dissipates. We vary the initial total mass and spatial distribution of the planetesimals, the time scale of dissipation of nebular gas (which dissipates uniformly in space and exponentially in time), and orbits of Jupiter and Saturn. We end up with 1-5 planets in the terrestrial region. In order to maintain sufficient mass in this region in the presence of Type I migration, the time scale of gas dissipation needs to be 1-2 Myr. The final configurations and collisional histories strongly depend on the orbital eccentricity of Jupiter. If today’s eccentricity of Jupiter is used, then most of bodies in the asteroidal region are swept up within the terrestrial region owing to the inward migration of the secular resonance, and giant impacts between protoplanets occur most commonly around 10 Myr. If the orbital eccentricity of Jupiter is close to zero, as suggested in the Nice model, the effect of the secular resonance is negligible and a large amount of mass stays for a long period of time in the asteroidal region. With a circular orbit for Jupiter, giant impacts usually occur around 100 Myr, consistent with the accretion time scale indicated from isotope records. However, we inevitably have an Earth size planet at around 2 AU in this case. It is very difficult to obtain spatially concentrated terrestrial planets together with very late giant impacts, as long as we include all the above effects of gas and assume initial disks similar to the minimum mass solar nebular.     

Oxidation of CO on surface hematite in high CO2 atmospheres

We propose a mechanism for the oxidation of gaseous CO into CO₂ occurring on the surface mineral hematite (Fe₂O₃(s)) in hot, CO₂-rich planetary atmospheres, such as Venus. This mechanism is likely to constitute an important source of tropospheric CO₂ on Venus and could at least partly address the CO₂ stability problem in Venus’ stratosphere, since our results suggest that atmospheric CO₂ is produced from CO oxidation via surface hematite at a rate of 0.4 petagrammes (Pg) CO₂ per (Earth) year on Venus which is about 45% of the mass loss of CO₂ via photolysis in the Venusian stratosphere. We also investigated CO oxidation via the hematite mechanism for a range of planetary scenarios and found that modern Earth and Mars are probably too cold for the mechanism to be important because the rate-limiting step, involving CO(g) reacting onto the hematite surface, proceeds much slower at lower temperatures. The mechanism may feature on extrasolar planets such as Gliese 581c or CoRoT-7b assuming they can maintain solid surface hematite which, e.g. starts to melt above about 1200 K. The mechanism may also be important for hot Hadean-type environments and for the emerging class of hot Super-Earths with planetary surface temperatures between about 600 and 900 K.     

A parallel global-implicit 2-D solver for reactive transport problems in porous media based on a reduction scheme and its application to the MoMaS benchmark problem

In this article, an approach for the efficient numerical solution of multi-species reactive transport problems in porous media is described. The objective of this approach is to reformulate the given system of partial and ordinary differential equations (PDEs, ODEs) and algebraic equations (AEs), describing local equilibrium, in such a way that the couplings and nonlinearities are concentrated in a rather small number of equations, leading to the decoupling of some linear partial differential equations from the nonlinear system. Thus, the system is handled in the spirit of a global implicit approach (one step method) avoiding operator splitting techniques, solved by Newton’s method as the basic algorithmic ingredient. The reduction of the problem size helps to limit the large computational costs of numerical simulations of such problems. If the model contains equilibrium precipitation-dissolution reactions of minerals, then these are considered as complementarity conditions and rewritten as semismooth equations, and the whole nonlinear system is solved by the semismooth Newton method.     

Population displacement after cyclone and its consequences: empirical evidence from coastal Bangladesh

This study investigates the disaster-induced population displacement scenario at individual household level in Bangladesh. ‘Population displacement’ is seen here as an alternative adaptation option to natural hazard for the survivors after cyclone Aila. The changes both in origin and destination community due to population displacement are described here on the basis of social ‘inclusion’ and ‘exclusion’ concept. The field survey was conducted during March–July 2010, and a sample of 280 respondents from 12 villages in southwest coastal Bangladesh was interviewed. Findings show that at the end of emergency aid, male members of the family started moving towards nearer cities to find an income. Based on the income and asset distribution at the community level, this study developed a societal cluster of displacement and demonstrates the societal changes because of cyclone-induced population displacement.