Post-collision neogene volcanism of the Eastern Rif (Morocco): magmatic evolution through time

Neogene volcanism in the Eastern Rif (Morocco) comprises a series of calc-alkaline, potassic calc-alkaline, shoshonitic and alkaline volcanic rocks. According to new stratigraphical, along with new and previous chronological and geochemical data, the orogenic volcanism was successively (1) calc-alkaline (basaltic andesites and andesites: 13.1 to 12.5 Ma, rhyolites: 9.8 Ma), (2) K-calc-alkaline (basaltic andesitic to rhyolitic lavas and granodiorites: 9.0 to 6.6 Ma), and (3) shoshonitic (absarokites, shoshonites, latites, trachytes: 7.0 to 5.4 Ma). The later Pliocene volcanism was basaltic and alkaline (5.6 to 1.5 Ma). The calc-alkaline and K-calc-alkaline series exhibit lower K₂O (0.7–5.3 wt.%), Nb (8–19 ppm) contents and higher ⁸⁷Sr/⁸⁶Sr (0.70773–0.71016) than the shoshonitic series (K₂O: 2.4–7.2 wt.%, Nb: 21–38 ppm, ⁸⁷Sr/⁸⁶Sr: 0.70404–0.70778). Pliocene alkaline basalts have a sodic tendency (Na₂O/K₂O: 1.7–3.5), high Nb content (up to 52 ppm), and low ⁸⁷Sr/⁸⁶Sr ratio (0.70360–0.70413). The variations through time of K₂O, Nb and Sr isotopic ratio reflect different mantle sources: (i) calc-alkaline, potassic calc-alkaline and shoshonitic series are derived from a mantle source modified by older subduction, (ii) alkaline basalts are derived mainly from an enriched mantle source. Through time, incompatible elements such as Nb increased while ⁸⁷Sr/⁸⁶Sr decreased, suggesting a decreasing influence of metasomatized mantle (inherited subduction). Such evolution is related to the post-collision regimes operating in this area, and could be linked to the succession of extensional, compressional and strike-slip fault tectonics.     

Thermal metamorphism of primitive meteorites—IX. On the mechanism of trace element loss from Allende heated up to 1400° C

We report data for Ag, Bi, Cd, Co, Cs, Ga, In, Se, Te, Tl and Zn determined by neutron activation in Allende samples heated for one week at 100° increments in the 1000–1400°C range in a low pressure (initially 10^?5atmH₂) environment using an apparatus of novel design. In the extremes, concentrations of these trace elements—initially present at ppm-ppb levels—in unheated material are lowered even farther by factors of 10^?4–10^?5 over a broad temperature span. Loss of some elements above 1000°C extends trends evident below 1000°C; loss of others is even more extreme. On Arrhenius diagrams some elements exhibit but one apparent activation energy over the entire temperature span of loss while others exhibit 2 or 3, each operative in a particular temperature region. These discontinuities seem related to mineralogic/petrologic alteration and probably reflect differences in diffusion mechanism rather than siting differences. The extension of previous experiments into the temperature regime postulated for chondritic differentiation should lead to a better understanding of the evolution of meteoritic parent bodies.     

Petrographie des Praezechsteins der Bohrung „Dransfeld l”

Core samples from the “Praezechstein” formation of the bore “Dransfeld 1” were investigated by optical, X-ray, and chemical methods. The rock formation consists of graywackes interbedded with Slates. The graywackes contain mineral.components and rock fragments which are also common in the graywackes of Harz and “Rheinisches Schiefergebirge”, so that a common source of derivation may be concluded, namely the “Mitteldeutsche Schwelle”. The distinctive features of the Dransfeld-graywackes however as compared to those of Harz and “Rheinisches Schiefergebirge” are:

1. 1.
   A higher content of rock fragments specially of volcanic origin.     

Evidence of the impacting body of the Ries crater — the discovery of Fe-Cr-Ni veinlets below the crater bottom

Fe-Cr-Ni particles and veinlets have been discovered in the top 15 m of the compressed zone with abundant shatter cones below the bottom of the Ries crater. The metallic particles are less than a few microns across. They occur in various minerals along healed intergranular and locally in intragranular microfractures in quartz diorite, amphibolite and chloritized granite of the basement crystalline rocks.The particles consist of major Fe, Cr, and Ni with minor Si and Ca. Origin due to contamination is absolutely ruled out. We believe that these Fe-Cr-Ni particles are probably condensed from the vaporized impacting body which produced the Ries crater. These particles were injected with high velocity into microfractures near the top of the compressed zone, implanted in and across various minerals before these microfractures were resealed. The presence of Si and Ca as well as the fact that the Cr content is nearly twice that of Ni, led us to conclude that the Ries impacting body is very likely not an iron meteorite but a stony meteorite.     

Paläoklimatische Information im Isotopengehalt14C-datierter Saharawässer: Kontinentaleffekt in D und18O

Zusammenfassung In den¹⁴C-Altern der Saharawässer spiegelt sich die wechselnde Abfolge von Feucht- und Trockenphasen während des späten Pleistozäns und Holozäns wider. Außerdem zeigt sich ein West-Ost-Gefälle in ihrem D- und¹⁸O-Gehalt, das als Kontinentaleffekt im Grundwasser gedeutet wird. Dieser Kontinentaleffekt setzt voraus, daß das nordafrikanische Klimageschehen vergangener Feuchtphasen von der Westdrift bestimmt wurde, die regenbringende atlantische Luftmassen weit ins Saharainnere getrieben hat. Ein einfaches mathematisches Modell, das den Kontinentaleffekt durch eine Rayleigh-Kondensation beschreibt, ergibt die beste Anpassung an die Meßwerte, wenn für die Sahara (ähnlich wie heute in Europa) ein West-Ost-Gefälle in den Paläo-Winterniederschlagsmengen von –30% pro 1000 km angenommen wird. Unter der Annahme ehemaliger Winterniederschläge (Sept.-März) von 600 mm (entspricht Lissabon heute) für das Gebiet an der nordafrikanischen Atlantikküste ergibt diese Modellrechnung z. B. 250 mm für die Paläo-Winterniederschläge im Gebiet des Murzuk-Beckens.

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The¹⁴C-age distribution of Saharian groundwaters shows the alternating sequence of humid and arid periods in the late Pleistocene and Holocene. The observed west-east decrease of the D- and¹⁸O-content of the Sahara waters is interpreted to be the Continental Effect in rain and groundwater. The paleoclimatic situation during ground-water formation therefore was controlled by the western drift carrying wet Atlantic air masses across the Sahara. The best fit of a simple Rayleigh condensation model of the continental effect to the experimental data is obtained with a west-east decrease of the Saharian paleo-winter precipitation of –30% per 1000 km (similar to the one in Europe today). With an annual winter precipitation rate (Sept.-March) of 600 mm (corresponding to the one of Lisboa today) for the Northafrican coastal area at the Atlantic Ocean a previous winter precipitation rate of 250 mm is obtained for the Murzuq Basin.

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Résumé Une succession de périodes humides et arides à la fin du Pléistocène et à l'Holocène se réflète dans la distribution des âges¹⁴C d'eaux souterraines du Sahara. Les teneurs en D et¹⁸O diminuent d'Ouest en Est, ce qui est interprété comme un effet continental dans l'eau souterraine. Celui-ci signifie que la climatologie des phases pluviales passées, dans l'Afrique du Nord, était déterminée par des vents d'Ouest qui apportaient des masses d'air atlantique humide à l'intérieur du Sahara. Un modèle mathématique simple décrivant l'effet continental par une condensation du type Rayleigh, reproduit avec la meilleure conformité les valeurs expérimentales, pour autant qu'on admette que les pluies hivernales au Sahara diminuaient anciennement d'Ouest en Est de 30% par 1000 km (comme à présent en Europe). En supposant qu'autrefois la quantité de pluie hivernale, de septembre à mars à la côte atlantique de l'Afrique du Nord était de 600 mm (comme aujourd'hui à Lisbonne), on obtient à l'aide de ce modèle une précipitation hivernale ancienne de 250 mm dans le bassin du Mourzouk.

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, ¹⁴C, . , ¹⁸O, , . , , , , . , Rayleigh, — , — — 30 % 1000 . , - , . . , 600 , — —, 250 .

     

Flow–duration curve integration into digital filtering algorithms for simulating climate variability based on river baseflow

ABSTRACT

A baseflow separation methodology combining the outcomes of the flow–duration curve and the digital filtering algorithms to cope with the restrictions of traditional procedures has been assessed. Using this methodology as well as the monitored and simulated hydro-climatological data, the baseflow annual variations due to climate change and human-induced activities were determined. The outcomes show that the long-term baseflow index at the upstream sub-basin is nearly half of that at the downstream from October to April, whereas they are close to each other for the remaining months. Some of the groundwater reacts to precipitation and an evident rise in the groundwater contribution was detected for the hydrological years 1998–2001 and 2006–2008. The contrary was recorded for1987. The water released from the reservoir in the dry periods led to distinctions in the detected baseflow index between the pre-damming and post-damming periods of the river.     

Causes of rockfalls in Al-Huwayshah area, Yemen

According to topography of Yemen, most areas and villages are located at obligated crest, toe of mountain and under cliffs. Therefore Al-Huwayshah consisting of Tawilah sandstone group is characterized by steep slope reach to 90° in some areas. This area is affected by strong tectonic movements and faults that occurred during the geological epochs. This effect enhances to find out fractures and joints as well as the rocks become brittle and ready to slide depending on the position of area. And there are some fractures and joints on the surface of the areas due to tectonic movement associated with opening the Red Sea and Gulf of Aden. The rainfalls, fractures, joints, earthquakes, gravity, vegetations, temperatures and human activities play a big role in the processes of rockfalls and landslides in this area. All those factors are considered as the basic causes and catalyzed factors for occurrence of rockfall in the studide area. In addition, the authors carried out laboratory test for many rock samples to get the physical properties of the rocks.     

Causes of rockfalls in Al-Huwayshah area,Yemen

According to topography of Yemen,most areas and villages are located at obligated crest,toe of mountain and under cliffs.Therefore Al-Huwayshah consisting of Tawilah sandstone group is characterized by steep slope reach to 90° in some areas.This area is affected by strong tectonic movements and faults that occurred during the geological epochs.This effect enhances to find out fractures and joints as well as the rocks become brittle and ready to slide depending on the position of area.And there are some frac...     

Slope stability FEM analysis and retaining wall design: a case study of clinker in Benxi of Liaoning

Stability is always the most important problem after high slope was excavated. The study analyzed the stress and strain inside the slope by Finite Element Method (FEM) and carried through stress distribution and failure zone, then analyzed the stability of the slope using three different methods and came to the conclusion that it is in unstable condition, so the designed retaining wall was put forward which makes the slope stable.     

A comparison of surface fitting algorithms for geophysical data

Many treatments in geophysics require regular grids of data. Since the data are generally recorded irregularly (e.g. gravity measurements along roads) or even on tracks (e.g. satellite measurements), it is necessary to grid the observed data. We present the result of a comparison of various surface fitting algorithms carried out in order to check their reliability. Two different types of sampling have been verified: (i) clouds of points and (ii) points along tracks. Five algorithms have been extensively tested: (1) polynomial fit, (2) algorithm using a combination of spline-laplace, (3) krigeage (4) least-squares fitting method, and (5) finite element method. The suitability of each method for different sets of data and the limitations (in terms of amplitude and gradient) are discussed.