The role of CO2 in the genesis of olivine melilitite

The nature of the near-liquidus phases for a mantle-derived olivine melilitite composition have been determined at high pressure under dry conditions and with various water contents. Olivine and clinopyroxene occur on or near the liquidus and there are no conditions where orthopyroxene crystallizes in equilibrium with the olivine melilitite. We have determined the effect on the liquidus temperature and liquidus phases of substituting CO₂ for H₂O on a mole for mole basis at 30 kb, using olivine melilitite + 20 wt% H₂O at = 0 and = (CO₂)/(H₂+CO₂) (mole fraction) = 0.25, 0.5, 0.75 and 1.0 (i.e. olivine melilitite + 38 wt% CO₂). Experiments were buffered by the MH or NNO buffers. At 30 kb, CO₂ is only slightly less soluble than water for <0.5 as judged by the slight increase in liquidus temperature on mole-for-mole substitution of CO₂ for H₂O and at 30 kb, 1200° C, = = 0.5 the olivine melilitite contains 8.8 wt% H₂O and 21 wt% CO₂ in solution. For 1 the CO₂ saturated liquidus is depressed 70 ° C below the anhydrous liquidus and the magma dissolves approx. 17% CO₂ at 30kb, 1400 ° C, 1, 0. Infrared spectra of quenched glasses have absorption bands characteristic of CO ₃ ⁼ and OH- molecules and no evidence for HCO ₃ ^- . The effect of CO ₃ ⁼ molecules dissolved in the olivine melilitite at high pressure is to suppress the near-liquidus crystallization of olivine and clinopyroxene and bring orthopyroxene and garnet on to the liquidus. We infer that olivine melilitite magmas may be derived by equilibrium partial melting (<5%) of pyrolite at 30 kb, 1150–1200 ° C, provided that both H₂O and CO₂ are present in the source region in minor amounts. Preferred conditions are 0< <0.5, 0.5< <1, and at low oxygen fugacities (相似文献   

Grenzen quantitativer Untersuchungen bei tektonischen Experimenten

Quantitative experimental and theoretical investigations, except basic research, should focus only to such parameters which can be measured in the field. This is shown by three examples.

1. A model of a discontinuum composed of particles, between which friction occurs during shear is presented. Even at simple shear external and internal stresses are in equilibrium; no rigid body rotation occurs. The theory is examinated experimentally.
2. In deformation experiments with clay and sand a development of anisotropy is observed, which can cause shear fractures. The orientation of the normal stress directions can be discovered from the shear sets, their angular distribution, and the rotation of the individual blocks.
3. Most folds can be traced back to the following three types, a) Similar folds, b) concentric folds, and c) box folds. b) and c) occur only near the surface and near shear planes, as shown by experiments and field observations. In all other cases the more energy-consuming similar folds are formed. Kink bands are presumably transitional between folds and shear fractures.

     

Hydrogeological mapping in Switzerland

The 1:500,000 geological, tectonic and hydrogeological maps of Switzerland have been updated using a new approach for a geographical information system (GIS). Geological, tectonic and hydrogeological data are combined in a single polygon data set. Specific data (point and line elements) are additionally represented on a separate GIS layer for each map respectively. The new 1:500,000 hydrogeological map of Switzerland consists of two different sheets. The first sheet provides information on the near-surface groundwater resources and qualitative estimates of their yield. The second sheet displays the groundwater resource vulnerability and the capacity of lateral contaminant transport. The 1:100,000 hydrogeological map of Switzerland shows the distribution and use of groundwater in a selected area. The near-surface consolidated and unconsolidated rocks are classified in this map according to their permeability and lithological and petrographical properties. The map is available as a pixel map.

---

Résumé  Les cartes aux 1:500,000 de la Suisse, portant sur la géologie, la tectonique et l’hydrogéologie, ont été mises à jour en utilisant une nouvelle approche pour un système d’information géographique (GIS, en anglais). Les données géologiques, tectoniques et hydrogéologiques ont été combinées sur un seul set de polygones. Les données plus spécifiques (points et lignes) sont représentées dans une couverture séparée, pour chaque carte respectivement. La nouvelle carte hydrogéologique de Suisse au 1:500,000 est constituée de deux différentes feuilles. La première feuille apporte des informations sur les ressources proches de la surface et sur leur rendement. La seconde feuille montre la vulnérabilité des ressources souterraines et le risque de pollution par transport latéral. La carte hydrogéologique de Suisse au 1:100,000 montre la distribution et l’utilisation de l’eau souterraine dans la région sélectionnée. Les roches consolidées ou meubles de sub-surface, sont classées au regard de leur perméabilité et de leurs propriétés lithologique et pétrographique. La carte est disponible pixellisée.

---

Resumen  Los mapas geológico, tectónico e hidrogeológico de Suiza a escala 1:500,000 han sido actualizados utilizando un nuevo enfoque para un sistema de información geográfico (SIG). Los datos geológicos, tectónicos e hidrogeológicos se combinan en un conjunto de datos en un solo polígono. Por otra parte, para cada uno de los mapas, los datos específicos (elementos puntuales y lineales) se representaron en una capa separa del SIG. El nuevo mapa hidrogeológico de Suiza a escala 1:500,000 contiene dos capas diferentes. La primera de ellas suministra información de los recursos hídricos subterráneos poco profundos y estimaciones cualitativas de sus rendimientos. La segunda capa muestra la vulnerabilidad de este recurso y el riesgo debido al transporte lateral de contaminantes. El mapa hidrogeológico de Suiza a escala 1:100,000 muestra la distribución y uso del agua subterránea en un área seleccionada. Los sedimentos consolidados y no consolidados cercanos a la superficie se clasifican en este mapa en función de su permeabilidad y propiedades litológicas y petrográficas. El mapa se encuentra disponible como un mapa de pixeles.

     

Luftdruckreihen der letzten zwei Jahrhunderte von Basel und Genf

Zusammenfassung Um die Temperaturschwankungen, die an weit zurückreichenden Reihen festgestellt werden, in Beziehung zu den Variationen der allgemeinen Zirkulation setzen zu können, wäre die Kenntnis der Luftdruckverteilung auch in früheren Jahrhunderten erwünscht. Als Beitrag zu dieser Fragestellung wurden in dieser Untersuchungen die weit zurückreichenden Luftdruckreihen von Basel (seit 1755) und Genf (seit 1768) durch Reduktion auf die jetzigen Standorte der meteorologischen Stationen homogenisiert. Die durch wechselnde Meereshöhe der Aufstellung oder durch Instrumentalfehler entstandenen Unstimmigkeiten wurden an Hand der Vergleichsreihen zuverlässiger Nachbarstationen eliminiert. Die ältesten Beobachtungen mußten mit Hilfe empirisch festgestellter Beziehungen auf 0°C reduziert werden. In zwei Tabellen im Anhang sind die reduzierten Monats-, Jahreszeiten- und Jahresmittel der beiden Stationen bis 1959 zusammengestellt. Außerdem ist zur Prüfung der Singularitäten der Jahresverlauf des Luftdrucks in Basel auf Grund ausgeglichener Tagesmittel für 7 je etwa 30jährige Teilperioden und für die Gesamtperiode wiedergegeben.

---

Summary In order to enable the examination of the relations of the temperature variations to those of the general circulation it would be desirable to know also the air pressure distribution in earlier centuries. For this purpose the long barometric series for Basle (dating back to 1755) and of Geneva (since 1768) have been homogenized by reduction to the present location of the meteorological stations. Inconsistencies caused by changes of the height of exposure or by instrumental errors have been eliminated by means of comparisons with reliable neighbouring stations. The oldest observations had to be reduced to 0°C by empirically determined relations. Two tables in the annex show the reduced monthly, seasonal and annual means of the two stations until 1959. For the examination of singularities, the annual variation of the air pressure for Basle by means of running means of the daily values for 7 partial periods of about 30 years each and for the whole period is shown.

---

Résumé Pour pouvoir mettre les variations séculaires de la température en relation avec les changements de la circulation générale, il serait désirable de connître la répartition de la pression aussi pour des anciens siècles. C'est à cet effet qu'on a réduit les observations barométriques de Bâle dès 1755 et celles de Genève dès 1768 aux niveaux actuels des baromètres respectifs. Des séries d'observations provenant d'autres stations permettent d'éliminer certaines inhomogénéités dues soit à des changements de l'emplacement des baromètres, soit à des erreurs instrumentales. Pour la réduction des lectures barométriques à la température de 0°C, on a dû faire appel à des relations empiriques. Les moyennes mensuelles, saisonnières et annuelles de la pression des deux stations jusqu'à 1959 sont communiquées dans deux tableaux en annexe. Finalement, on a reproduit pour Bâle les moyennes journalières pour 7 périodes différentes d'environ 30 ans chacune et pour la période totale des observations pour permettre d'étudier les singularités météorologiques.

---

---

Mit 7 Textabbildungen     

Numerical approximation of water–air two-phase flow by the mixed finite element method

A new model for two-phase flow of water and air in soil is presented. This leads to a system of two mass balance equations and two equations representing conservation of momentum of fluid and gas, respectively. This paper is concerned with the verification of this model for the special case of a rigid soil skeleton by computational experiments. Its numerical treatment is based on the Raviart–Thomas mixed finite element method combined with an implicit Euler time discretization. The feasibility of the method is illustrated for some test examples of one- and two-dimensional two-phase flow problems.     

Continental rift-setting and evolution of Neoproterozoic Sindreth Basin in NW-India

The Neoproterozoic Sindreth Basin, NW India, and its surrounding area represent a half graben structure situated between the undeformed Malani Igneous Suite (MIS) in the west and a corridor of coeval Cryogenian ductile deformation, anatexis and granite intrusion in the east. The main lithologies observed in the basin are conglomerate, fanglomerate, debris flow and lake deposits derived from a nearby continental provenance, intercalated with concurrent mafic and felsic lava flows. Based on geological traverses across the strike of the basin, we propose a three-fold classification comprising Lower Clastic Unit and an Upper Clastic Unit and a Bimodal (basalt–rhyolite) Volcanic Unit separating the two. Tilting due to basin inversion and faulting has been observed; however, the rocks are unmetamorphosed and show undisturbed primary sedimentary features. The stratigraphic record of the basin is characteristic for deposition and magmatism in a fault-related continental setting. Implications of the findings have been discussed in the context of Neoproterozoic crustal dynamics in NW India. This study provides conclusive evidence for a continental setting for Sindreth Basin evolution and contests the recent models of active subduction setting (either back-arc basin or accretionary sediments over a subduction zone).     

Conventional and ion-microprobe U-Pb dating of detrital zircons of the Tentudía Group (Serie Negra,SW Spain): implications for zircon systematics,stratigraphy, tectonics and the Precambrian/Cambrian boundary

Conventional multi-grain and ion-microprobe dating of detrital zircons from a very low grade metagraywacke of the Tentudía Group (upper part of the Serie Negra, Ossa-Morena Zone, SW Spain) reveals an uppermost Vendian age for the deposition of the metagraywacke. The youngest detrital zircon grain provides a maximum depositional age of about 565 Ma. Thus, these data contradict earlier Middle to Upper Riphean (ca. 1350-850 Ma) estimates on the age of the Tentudía Group and favour a Precambrian/Cambrian boundary falling into the range of 540 to 530 Ma. The presence of about 20% of Pan-African detrital zircons ranging from about 700 to 550 Ma indicates the derivation from Gondwana. From the upper intercept ages of the fan-shaped data field defined by conventionally determined zircon fractions, it can be deduced that 2.1 Ga old zircons as well as Archean zircons existed in the provenance(s) of the Serie Negra sediments. This mixing of crustal components of different ages is in line with the Nd crustal residence age of 1.9 Ga. The latter value, as well as other model ages of the Iberian Massif, indicates unusually high amounts of ancient crust to be present in the strata. This is different to other (meta)sediments of the European Hercynides and suggests that the Iberian strata of uppermost Precambrian age may contain the detritus of more internal, older parts of Gondwana than other European strata of comparable ages. Geochemical data on the analysed sample and further metagraywackes of the Tentudía Group argue for a deposition in an arc environment. Such a scenario would conform with the syn- to post-orogenic shallow marine deposition of the studied sediments. Furthermore, an upper time limit for the pre-Lower Cambrian deformational history, including two phases of regional deformation, is given by the maximum age of deposition, implying a very short time interval for deposition and deformation of the Tentudía Group. Concerning the U-Pb systematics of detrital zircon fractions, it is probable that numerous, previously published conventional multi-grain zircon data on (meta)sedimentary rocks of the European Hercynides readily can be explained by the presence of up to 20% of Pan-African detrital zircons and later Phanerozoic lead loss during metamorphic transformation of the sedimentary protoliths. Moreover, this implies that such metasediments originated from post-Pan-African sedimentary precursors.     

The rhombohedral framework of the Scandinavian Caledonides and their foreland

The Baltic Shield of northern Europe is transsected by approximately N-S and NW-SE striking Proterozoic fault and fracture zones that were remobilized during the Late Precambrian opening of the Iapetus ocean and the SE-directed thrusting of the Caledonian nappes in Mid-Paleozoic time. Remobilizations of these older structures account for a distinct subsidence history and sedimentological evolution over each fault-bounded basement segment during opening of the Iapetus and for a distinct metamorphic and structural development found within each block during overthrusting of the Caledonian nappes and the exhumation of the orogen. The two fault sets define basement blocks with rhombus-like plan sections which had individual subsidence histories during Iapetus rifting as is expressed by their Late Precambrian (Riphean and Vendian) to Silurian sedimentary cover of contrasting thickness and facies. This contrasting subsidence history of the various basement blocks may have contributed to differences in thrusting level, thrust excision (nappe size), and tectonic style. Correlative Caledonian nappes from adjacent faultbounded basement blocks were thrust diachronously resulting in transport transverse to the general thrusting direction. Thrusting oblique to the NW-SE fault zones and orogen parallel extension resulted in lateral-ramp folds in the cover and reactivation along the NW-SE faults imbricated the overlying nappes. The extent of basement imbrication and duplex formation is variable in the different segments. Within single segments, the basement imbrication and duplex-formation defined basement highs that roughly align in two parallel zones within the orogen. The site of the basement duplexes is probably controlled by older N-S fracture zones while the pinch- and-swell structure parallel to the orogen is caused by the individual deformation and thrusting behavior of the basement and cover sequences that are bound by the NW-SE fault zones. Thus the Caledonian orogen appears to have inherited the Precambrian structural grain of the underlying, Baltic Shield.

---

Zusammenfassung Der Baltische Schild Nordeuropas ist von im Proterozoikum angelegten Verwerfungen und Scherzonen mit nördlichem sowie und nordwestlichem Streichen durchzogen, welche während der spätpräkambrischen Öffnung des Iapetus-Ozeanes und der anschließenden, südöstlich gerichteten Überschiebung der kaledonischen Decken im ausgehenden Alt-Paläozoikum reaktiviert worden sind. Die Wiederbelebung dieses ererbten, durch steilstehende Störungen gekennzeichneten, rhombenförmigen Strukturmusters führte zu unterschiedlichen Absenkungsraten der Störungsbegrenzten Grundgebirgsblöcke und steuerte somit die Ablagerungsbedingungen in entstehenden Sedimentationströgen während der Öffnungsphase des Iapetus-Ozeans. Durch diesen Prozeß lassen sich latterale Unterschiede in Mächtigkeit und Fazies der jungpräkambrischen bis altpaläozoischen Deckensedimente entlang dem Nordwestrande des damaligen Kontinentes Baltica, sowie Differenzen in der metamorphen und strukturellen Entwicklung der durch Störungen begrenzten Blöcke während der Überschiebung der kaledonischen Decken und der Hebung des Gebirges erklären. Vertikale Blockverschiebungen und Kippungen von Blöcken relativ zueinander können beobachtete Unterschiede in den Abscherungs- und Überschiebungsniveaus, sowie unterschiedliche tektonische Baustile auf und vor (vor allem) zwischen Blöcken erklären helfen. Untereinander korrelierbare kaledonische Deckensegmente haben, in Bezug auf Transportrichtung und Strecke, voneinander unterschiedliche Wege oberhalb ihrer Untergrundsegmente zurückgelegt. Während dieser Überschiebung auf ein sich simultan veränderndes Relief ist es dabei zu Teilbewegungen schräg zur Hauptüberschiebungsrichtung gekommen, was seinerseits zu seitlichen Verzahnungen benachbarter Deckensegmente geführt hat. Die NWSE streichenden Blockgrenzen haben während lokaler Überschiebungen leicht schräg zu dieser Hauptrichtung als Widerlager und Rampen (lateral ramps) für die darübergleitenden Decken gewirkt, welche sich ihrerseits bei diesem Prozeß in orogentransversale Falten gelegt haben. Je nach ihrer Lage und Neigung sind die verschiedenen Segmente während der Kollisionsphase des kaledonischen Orogens in unterschiedlichem Grade von internen Störungen betroffen worden. Die durch intensive Internscherung hervorgerufenen Krustenverdickungen zeigen eine perlschnurartige Anordnung in zwei orogenparallele zonen, deren Anlage sich auf unterliegende und mitverfrachtete N-S Störungszonen zurückführen lassen kann. Das Anschwellen und Ausdünnen (pinch- and-swell) von tektonischen Einheiten entlang der Längsrichtung des Orogens läßt sich durch unterschiedliche Deformationsverhalten innerhalb der durch NW-SE Störungen begrenzten Segmente erklären. Die Kaledoniden Skandinaviens haben offensichtlich das strukturelle Gepräge ihrer präkaledonischen Unterlage ererbt.

---

Résumé Le bouclier baltique est traversé par des fractures protérozoïques orientées approximativement N-S et NW-SE. Ces failles furent réactivées d'abord au Précambrien tardif lors de l'extension correspondant à l'ouverture de l'Océan lapétus, ensuite au Protérozoïque moyen lors du charríage des nappes calédoniennes vers le SE. La réactivation de ces vieilles structures explique qu'on observe pour chaque bloc du socle faillé une subsidence et une sédimentation différente pendant la phase d'extension (ouverture du lapétus), ainsi qu'une évolution métamorphique et structurale distincte pendant le charriage des nappes calédoniennes et l'exhumation de l'orogène. Les deux groupes de failles définissent dans le socle des blocs à sections rhombiques qui présentaíent chacun une subsidence particulière pendant l'ouverture du lapétus, comme l'indiquent les variations d'épaisseur et de facies de leur couverture sédimentaire tardi-précambrienne (vendienne) à silurienne. Cette subsidence variable selon les blocs pourrait avoir contribué à induire des différences dans les niveaux de décollement et de charriage des nappes, ainsi que dans le style tectonique. Les unités tectonostratigraphiques des blocs adjacents furent charriées de façon diachronique avec comme résultat un transport transverse par rapport à la direction dominante du charriage. Ce déplacement oblique vers les zones de failles NW-SE et l'extension parallèle de l'orogène ont produit des plis transversaux dans la couverture; la réactivation des failles NW-SE s'est traduite par l'imbrication des nappes surincombantes. L'importance de cette imbrication et de la formation de duplex est variable selon les différents segments du socle. Pour chaque segment particulier, l'imbrication du socle et la formation de duplex ont engendré des culminations de socle alignés selon deux zones parallèles dans l'orogène. La position des duplex est probablement régie par de vieilles failles N-S alors que la structure en «pinch- and-swell» le long de l'orogène est causée par le caractère individuel de la déformation et du charriage du socle et de sa couverture, propre à chaque bloc limité par des failles NW-SE. L'orogenèse calédonienne a été ainsi fortement afffectée par les structures précambriennes du bouclier baltique sous-jacent.

---

, lapetus - . , , , , , lapetus. - - , , . , , , . , , . , . NW-SE (»side-wall ramps«) , . . , , , ; , , , - . (pinck- and-swell) , , NW-S . , - .

     

Impact of Preboreal to Subatlantic shifts in climate on groundwater resources on the Arabian Peninsula

A large-scale numerical flow and transport model was developed for the central-eastern arid part of the Arabian Peninsula. The model was applied to a region with freshwater resources dating back to more humid periods of the past, which are faced with overexploitation today. Model inflow was based on infiltration around wadi beds and groundwater recharge. Inflow was balanced by natural outflows, such as evaporation from sabkhas, spring discharge, and discharge to the sea. Two models were developed: (1) a short-term present-day model to estimate effective model parameters, and (2) a long-term model to study the development of the groundwater resources during the Mid- and Late Holocene and the natural response of the groundwater system to changes in climate. Hydraulic model parameters (hydraulic conductivity and specific storage) were assigned with respect to geological structures. Hydraulic parameters were estimated with an inverse PEST model by calibrating against observed depression cones cause by groundwater abstraction. Sensitivity analysis demonstrated that estimated model parameters were associated with a high uncertainty at a certain distance from agricultural areas when calibration data were lacking. A long-term model starting 10,000 years BP was calibrated by spring discharge and palaeo-groundwater levels and validated using measured ¹⁴C groundwater ages. The long-model predicted that groundwater levels adapted in response to changes in precipitation. During the Mid-Holocene, which was characterized by an intensification of the monsoon season, groundwater levels increased by 10 m on the mainland within the shallow aquifers and adapted quickly to higher recharge rates. The deeper aquifers were less affected by changes in climate. Along the present-day coastline, the groundwater level rose by about 25 m due to the declined sea level in the Mid-Holocene. During this period, surface run-off was possible as groundwater levels temporarily reached the ground surface. The natural groundwater budget reacted sensitively to changes in climate. Between 10 and 3 ka, groundwater storage occurred. During the Late Holocene, at 3 ka, natural depletion of the groundwater system began, which still prevails today.