High‐P tectono‐metamorphic evolution of mylonites from the Variscan basement of the Northern Apennines,Italy

Strain localization within shear zones may partially erase the rock fabric and the metamorphic assemblage(s) that had developed before the mylonitic event. In poly‐deformed basements, the loss of information on pre‐kinematic phases of mylonites hinders large‐scale correlations based on tectono‐metamorphic data. In this study, devoted to a relict unit of Variscan basement reworked within the nappe stack of the Northern Apennines (Italy), we investigate the possibility to reconstruct a complete pressure (P)–temperature (T)–deformation (D) path of mylonitic micaschist and amphibolite by integrating microstructural analysis, mineral chemistry and thermodynamic modelling. The micaschist is characterized by a mylonitic fabric with fine‐grained K‐white mica and chlorite enveloping mica‐fishes, quartz, and garnet pseudomorphs. Potassic white mica shows Mg‐rich cores and Mg‐poor rims. The amphibolite contains green amphibole+plagioclase+garnet+quartz+ilmenite defining S₁ with a superposed mylonitic fabric localized in decimetre‐ to centimetre‐scale shear zones. Garnet is surrounded by an amphibole+plagioclase corona. Phase diagram calculations provide P–T constraints that are linked to the reconstructed metamorphic‐deformational stages. For the first time an early high‐P stage at >11 kbar and 510°C was constrained, followed by a temperature peak at 550–590°C and 9–10 kbar and a retrograde stage (<475°C, <7 kbar), during which ductile shear zones developed. The inferred clockwise P–T–D path was most likely related to crustal thickening by continent‐continent collision during the Variscan orogeny. A comparison of this P–T–D path with those of other Variscan basement occurrences in the Northern Apennines revealed significant differences. Conversely, a correlation between the tectono‐metamorphic evolution of the Variscan basement at Cerreto pass, NE Sardinia and Ligurian Alps was established.     

Examining ambient noise using colocated measurements of rotational and translational motion

In the past decade, a number of studies have reported the observation of rotational motion associated with seismic events. We report a first observation of rotational motion in the microseismic ambient noise band. A striking feature of rotational motion measurements is that the information about the seismic phase velocity and source back azimuth is contained in the amplitude ratio of a point measurement of rotation rate and transverse acceleration. We investigate the possibility of applying this method to ambient noise measured with a ring laser and a broadband seismometer at the Wettzell Geodetic Observatory in Germany. Using data in the secondary microseismic band, we recover local phase velocities as well as the back azimuth of the strongest noise source for two different time periods. In order to confirm these findings, we additionally compare the results with classical array processing techniques of the Gr?fenberg array located nearby.     

Strain rotation coupling and its implications on the measurement of rotational ground motions

Spatial derivatives of the seismic wave field are known to be sensitive to various site effects (e.g., cavity effects, topography, and geological inhomogeneities). In this study, the focus is on strain rotation coupling that can cause significant differences between point measurements compared to array-derived rotational motions. The strain rotation coupling constants are estimated based on finite element simulations for inhomogeneous media as well as for the 3D topography around Wettzell, Germany (the location of the G ring laser). Using collocated array and ring laser data, the coupling constants of the ring laser itself are shown to be small. Several examples are shown to illustrate the order of magnitude that strain-induced rotation might have on the seismograms in the near field of volcanoes as well as in the far field and in the low-frequency spectrum (free oscillations).     

Improving the assessment of uncertainty and risk in the spatial prediction of environmental impacts: a new approach for fitting geostatistical model parameters based on dual Kriging in the presence of a trend

Modern methods of geostatistics deliver an essential contribution to Environmental Impact Assessment (EIA). These methods allow for spatial interpolation, forecast and risk assessment of expected impact during and after mining projects by integrating different sources of data and information. Geostatistical estimation and simulation algorithms are designed to provide both, a most likely forecast as well as information about the accuracy of the prediction. The representativeness of these measures depends strongly on the quality of the inferred model parameters, which are mainly defined by the parameters of the variogram or the covariance function. Available data may be sparse, trend affected and of different data type making the inference of representative geostatistical model parameters difficult. This contribution introduces a new method for best fitting of the geostatistical model parameters in the presence of a trend, which utilizes the empirical and theoretical differences between Universal Kriging and trend-predictions. The method extends well known approaches of cross validation in two aspects. Firstly, the model evaluation is not only limited to sample data locations but is performed on any prediction locations of the attribute in the domain. Secondly, it extends the measure used in cross validation, based on a single point replacement by using error curves. These allow defining rings of influence representing errors resulting from separate variogram lags. By analyzing the different variogram lags the fit of the complete covariance can be assessed and the influence of the several model parameters separated. The use of the proposed method in an EIA context is illustrated in a case study related on the prediction of mining-induced ground movements.     

作为生态和环境保护手段的空间规划:联邦德国的经验及对中国的启示

联邦德国生态环境保护走过了一条污染-治理-预防的道路, 即由技术性和应激性转为政策性和预防性的环境保护。生态环境保护政策和措施由环保活动家,大企业,学术界,地方及联邦各级有关部门共同制定,并由一个国家级综合的监测体系监督执行。公众不仅有权力了解结果,而且也将参与政策措施的制订和监督。德国空间规划包含欧盟,联邦,州,区域,城镇和城市建设6个层面。空间规划,特别是生态环境规划已成为预防生态环境破坏的重要措施。然而,联邦德国生态环境规划实施也面临个人交通和小企业污染以及环保成本提高造成企业区位劣势所带来的挑战。这些经验教训对中国的生态环境保护目标,政策措施的完善及生态空间规划的制订和监督落实,环境评价,特别是规划本身的环境评价具有借鉴意义。具体包括4个方面: 1)生态环境保护政策实现从提高环保技术手段向预防污染产生转变; 2)保证生态环境保护政策及实施的有效性; 3)把空间规划作为实现区域经济和社会稳定可持续发展的手段,提高生态和环保目标的地位; 4)在规划的技术层面上关注居住,休闲,交通和自然保护区用地的增长。     

A depositional model for the terminal Neoproterozoic–Early Cambrian Ara Group evaporites in south Oman

Abstract Six evaporite–carbonate sequences are recognized in the terminal Neoproterozoic–Early Cambrian Ara Group in the subsurface of Oman. Individual sequences consist of a lower, evaporitic part that formed mainly during a lowstand systems tract. Overlying platform carbonates contain minor amounts of evaporites and represent transgressive and highstand systems tracts. Detailed sedimentological and geochemical investigation of the evaporites allowed reconstruction of the depositional environment, source of brines and basin evolution. At the beginning of the evaporative phase (prograding succession), a shallow-water carbonate ramp gradually evolved into a series of shallow sulphate and halite salinas. Minor amounts of highly soluble salts locally record the last stage of basin desiccation. This gradual increase in salinity contrasts sharply with the ensuing retrograding succession in which two corrosion surfaces separate shallow-water halite from shallow-water sulphate, and shallow-water sulphate from relatively deeper water carbonate respectively. These surfaces record repeated flooding of the basin, dissolution of evaporites and stepwise reduction in salinity. Final flooding led to submergence of the basin and the establishment of an open-water carbonate ramp. Marine fossils in carbonates and bromine geochemistry of halite indicate a dominantly marine origin for the brines. The Ara Group sequences represent a time of relatively stable arid climate in a tectonically active basin. Strong subsidence allowed accommodation of evaporites with a cumulative thickness of several kilometres, while tectonic barriers simultaneously provided the required restricted conditions. Subsidence allowed evaporites to blanket basinal and platform areas. The study suggests a deep-basin/shallow-water model for the evaporites.     

Zur Entwicklung von Riftsystemen im Frühstadium (Hebung — Spaltung — Vulkanismus — Spreading) am Beispiel der Afar Senke

A combination of palaeomagnetic, seismological, gravitational, aeromagnetic and geochemical observations, as well as geological and regional considerations are strongly indicative of anticlockwise rotational movements of the Danakil Alps and formation of new oceanic crust in the Northern Afar Triangle. The decreasing amount of spreading in the Southern Red Sea is compensated by en chelon crustal spreading (formation of oceanic crust in a continental environment) in the Danakil-Afar Depression. Here, the geophysical properties are generally intermediate between the more typical continental (Ethiopia) and oceanic (Red Sea, Gulf of Aden) data. Such intermediate type crust is proposed to be caused by “oceanization” of formerly continental crust, i. e. fragmentation and basification through massive dyke injections (mantle diapirism). The structure and evolution of the wider Afar Triangle, East-African Rift System, Red Sea and Gulf of Aden are used to derive a model for possible stages during initial continental break-up and compared with selected, similarly structured parts of the n-Atlantik. The continental break-up probably develops in the following stages: 1. general uplift associated with surface fracturing above an asthenospheric diapir (uplift), 2. development of linear “Scheitel”-Grabensystems along the crest of the uplift or uplift chains (rupture), 3. graben with (contaminated) volcanism stage (volcanism), 4. “oceanization” of the developing depression through fragmentation and basification by massive oceanic and/or contaminated dyke-injections of the former continental crust along several sporadically active lineaments, 5. “crustal spreading” on land or concentration of mantle derived, oceanic crust-injections along one major lineament in a dry, continental environment, 6. “evaporit-stage of sea-floor spreading” with sporadic seawater connections to an open marine basin and 7. “ocean-floor spreading” in the deep-sea environment of advanced oceanic troughs. The derivation of these stages basically involves the addition of “sea-floor spreading” processes (oceanization, crustal-, sea- and ocean-floor spreading) to the well known sequence: Hebung — Spaltung — Vulkanismus (Cloos, 1939) and relate it to mantle-diapirism processes. All the above stages are recognizable along the Afro-Arabian Rifts and seem to have morphological equivalents in the Atlantic.     

Über sprunghafte Änderungen von Funkpeilungen nach Consol-Funkfeuern bei Nacht

Zusammenfassung Wenn man Consol-Funkfeuer unabhängig von ihrer Eigenschaft als Leitstrahlsender mit einem Rahmenpeiler, insbesondere mit Sichtpeilapparatur, beobachtet, ergeben sich bei Nacht während der Umtastperiode häufig verschiedene Peilrichtungen für die beiden Tastzustände der Consol-Aussendung. Dadurch entstehen für den Beobachter am Sichtfunkpeiler sprunghafte Änderungen der Peilanzeige, die im Rhythmus der Umtastung erfolgen. Es wird gezeigt, daß sich dieser Effekt durch die Überlagerung der Bodenwelle und einer anomal polarisierten Raumwelle, die am Ort des Peilers auftritt, erklären läßt.

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On sudden changes in radio direction finding indications of Consol stations by night

Summary Regardless of their character as radio range beacons Consol stations may be observed with a normal radio direction finder. Using a direction finder with loop aerial system it will be noticed — particularly when a cathode ray direction finder is used — that by night during the dot-dash-period of the Consol transmission different bearings for the dots and for the dashes are often observed. Hence, the operator at the visual direction finder perceives sudden changes of the bearing indications occurring in the dot-dash-rhythm. It is shown that this effect can be explained by the superposition of the ground-wave and an anomally polarized sky-wave, both being present at the place of the direction finder.

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Sur des changements subits des relèvements radiogoniométriques observés aux radiophares Consol pendant la nuit

Résumé Indépendamment de leur qualité de radiophares directifs, les radiophares Consol peuvent être observés, comme des transmetteurs normaux, à l'aide d'un radiogoniomètre à cadre. Pendant la période de renversement des courants d'antennes Consol, on remarque souvent de nuit — surtout si l'on se sert d'un radiogoniomètre à lecture visuelle — différents gisements de relèvements dans les deux phases de l'émission Consol. L'observateur devant le goniomètre visuel remarquera, donc, que les indications radiogoniométriques sont soumises aux changements subits suivant le rhythme des renversements de la manipulation Consol. On montre que cet effet est dû à la superposition de l'onde directe par une onde réfléchie et anomalement polarisée se manifestant auprès de la place du goniomètre.

     

Diagenetische Veränderungen in den Rotliegend Sandsteinen im NW-Deutschen Becken

Zusammenfassung Mit seinen auf 3000 m bis 6000 m versenkten Schichten bildet das Rotliegende in Nordwestdeutschland eine Gasprovinz, deren Lagerstätten-Inhalte aus dem Karbon im Liegenden abgeleitet werden. Die Reservoire sind Sandsteine, die mit Tonsteinen wechsellagern. Sie wurden nach einer Phase reger vulkanischer Aktivität des untersten Perm als red bed-Sedimente in einem ariden Klima abgelagert.Das Untersuchungsgebiet ist der Raum zwischen Weser und Elbe. Es wurde versucht, eine grundsätzliche Teufen/Porositäts-Variation der Sandsteine zu erarbeiten, was wegen der komplexen Gefügebedingungen sehr schwierig ist. In diesem Zusammenhang ergab sich die Markierung des Endes der mechanischen Kompaktion bei einer Porosität um 22% für feinkörnige Sandsteine.Die in den Poren (epigenetisch) ausgefällten allochemischen Zementminerale zeigen Merkmale einer synsedimentären bis frühdiagenetischen Kristallisation. Nicht zuletzt kommt das in der regionalen paläogeographischen Anordnung der Zementminerale Karbonat, Sulfat und Halit zum Ausdruck, in dieser Reihenfolge zunehmend evaporitischen Charakters vom Beckenrand im Süden zur Beckenachse im Norden hin bevorzugt verteilt.In den Intergranularen der Sandsteine sind authigene Tonminerale weit verbreitet, besonders als Coating- und Overgrowth-Gefüge. Die Reaktion von Feldspat und die gesteigerte Authigenese von Tonmineralen in einem Gebiet, in dem die gewöhnlich anzutreffenden Effusivgesteine im Liegenden fehlen, werfen ein Licht auf die Herkunft dieser Tonminerale und auf die Migrationsvorgänge.

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With its sequences attaining depths of 3000 to 6000 m, the Rotliegend in NW Germany forms a gas province whose reservoir contents are derived from underlying Carboniferous. The reservoirs consist of sandstones alternating with shales, which were deposited in an arid climate as red bed sediments after a phase of intensive volcanic activity in the lowermost Permian.The investigated area is situated between the rivers Weser and Elbe. It was tried to obtain a basic depth/porosity variation of the sandstones, a rather difficult attempt because of the very complex fabric conditions. In this connection the end of the mechanical compaction could be marked at a porosity of about 22% for fine-grained sandstones.The allochemical cement minerals precipitated (epigenetically) in the pores show features of a synsedimentary to early-diagenetic crystallisation. This is not least reflected in the regional paleogeographic distribution of the cement minerals carbonate, sulfate and halite which, in the order of their listing, become more evaporitic, with increasing proportions from the basin margin in the south towards the basin axis in the north.In the intergranulars of the sandstones, authigenic clay minerals occur frequently, in particular in the form of coating and overgrowth. Reaction of feldspar and advanced authigenesis of clay minerals in an area where the generally occurring effusive rocks are missing in underlying formations give an idea of the genesis of clay minerals and of migration processes.

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Résumé Le Rotliegend constitue au nord-ouest de l'Allemagne une province à gisements de gaz naturel. Les réservoirs consistent en grès alternant avec des argiles, qui ont subi un affaissement de 3000 à 6000 m. Ces couches sont des »sédiments rouges« déposés dans un climat aride après une phase d'activité volcanique intense dotant du permien le plus inférieur. Le gaz provient du carbonifère.La région étudiée est située entre le Weser et l'Elbe. On a eu en vue la variation fondamentale entre la profondeur et la porosité des grès, tâche assez difficile en raison des conditions de texture très complexes. A cette occasion on a pu enregistrer la fin de la compaction mécanique avec une porosité de 22% environ pour les grès fins.Les minéraux allochémiques du ciment préciptés (épigénétiquement) dans les pores montrent les caractéristiques d'une cristallisation synsédimentaire à protodiagénétique. Cela se manifeste aussi dans la distribution paléogéographique régionale des minéraux du ciment, carbonate, sulfate et halite, qui deviennent dans cet ordre, de plus en plus évaporitiques à partir du bord méridional du bassin vers son axe; en d'autres termes les minéraux les plus évaporitiques sont déposés vers le nord.Dans les pores des grès, les minéraux d'argile authigènes sont très répandus, en particulier sous forme d'une pellicule enveloppante et d'enrobement. La réaction de feldspath et l'authigenèse avancée des minéraux d'argile dans une région où les roches effusives normalement présentes sont absentes les couches inférieures, permettent de se faire une idée de la genèse des minéraux d'argile et des processus de la migration.

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