A nocturnal low level jet during PUKK

A nocturnal low-level jet characterized by a distinct inertial oscillation lasting from around sunset until sunrise the next day was observed during the coastal experiment PUKK. The phenomenon appeared over an area of at least 40 km in diameter; it thus had a mesoscale extension. We were able not only to observe this fine case but also to simulate it by an integrated dynamical PBL model.     

Radon emanometry in soil gases and activity in ashes from El Chichon Volcano

Radon (²²²Em) emanation measurements in soil gases are reported in connection with the 1982 eruptions of El Chichón Volcano.²²²Em detection is performed with LR-115 cellulose nitrate track detectors. Results show a general decreasing pattern of²²²Em concentration in soil with time after the eruptions. Activity measurements of radon daughters in ashes show that a large amount of²²²Em and²²⁰Em was released from magma degassing during the eruptions, and that only a fraction of the degassed magma was erupted. An important fluid interaction between the magma chamber and the surrounding sedimentary rock is also suggested.     

Chloritoid-bearing metapelites associated with glaucophane rocks in western Crete,Greece

In western Crete, Greece, a widespread occurrence of chloritoid-bearing metapelites with the main mineral assemblage chloritoid-phengitic white mica-Fe-rich chlorite-quartz was recorded to form the country rock of glaucophane-bearing metabasalts. Six bulk rock analyses of the metapelites conform to the compositional restrictions evaluated by Hoschek (1967) for the formation of chloritoid. Three microprobe analyses revealed chloritoid compositions low in Mg and Mn, and, consequently, high in Fe. The metamorphic grade documented in the metapelites is obviously related to a subsequent prograde metamorphism by which, in the adjacent meta-basalts, epidote is formed at the expense of lawsonite. No relict of a high-P, low-T assemblage, in part well preserved in the meta-basalts, was recognized in the chloritoid schists. The significance of the metamorphic history is briefly discussed.     

Ein verbessertes Strukturmodell für die Ostalpen,abgeleitet aus refraktions-seismischen Daten unter Berücksichtigung des Alpen-Längsprofils

Zusammenfassung Die Vermessung des Alpen-Längsprofils 1975 lieferte unter anderem Daten zur verbesserten Bestimmung der Geschwindigkeits-Tiefen-Verteilung unter dem Alpen-Hauptkamm. Diese Geschwindigkeits-Tiefen-Verteilung ist charakterisiert durch eine mächtige Inversionszone im Tiefenbereich zwischen 20 und 30 km — sie liegt somit tiefer als bei früheren Modellen — sowie eine weitere weniger ausgeprägte Inversionszone in der Unterkruste. Eine mit diesen Ergebnissen konsistente Reinterpretation des EschenloheSüdost-Profils ermöglichte die Konstruktion eines zweidimensionalen Krustenmodells längs der Linie Eschenlohe-Triest. Dieses Modell ist auch in guter Übereinstimmung mit Ergebnissen der Refraktionsprofile Eschenlohe-Ost und Lago Lagorai-Ost. Darüber hinaus befriedigt es Laufzeitbeobachtungen von Nachbeben aus der Region Friaul.

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Refraction seismic measurements along the Alpine Longitudinal Profile 1975 yielded among other things data for a reliable determination of the velocity-depth distribution beneath the crest of the Alps. This velocity-depth distribution is characterized by a rather thick inversion zone in the depth range between 20 and 30 km — which is deeper than with earlier models — as well as another less pronounced one in the lower crust. A reinterpretation of the Eschenlohe-Southeast profile consistent with these new data allowed the development of a two-dimensional crustal model along the line Eschenlohe-Trieste. This model is in excellent agreement with results from refraction profiles Eschenlohe-East and Lago Lagorai-East. It furthermore satisfies travel time observations from aftershocks of the Friulian earthquake.

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Résumé La campagne ALP 1975 a permis entre autres de donner une meilleure détermination de la répartition de la vitesse en profondeur v(z) sous la crête principale des Alpes. Celle-ci est caractérisée par une épaisse zone d'inversion de vitesse (LVZ) entre 20 et 30 km, donc plus profonde que les modèles antérieurs, et une seconde zone d'inversion moins prononcée dans la croûte inférieure. Tenant compte de ces résultats nous avons fait une réinterprétation du profil Eschenlohe-Sud-Est, ce qui nous permet de construire une coupe structurale de la croûte le long de la ligne Eschenlohe-Trieste. Ce modèle est en bon accord avec les résultats des profils Eschenlohe-Est et Lago Lagorai-Est et avec des durées de propagation déterminées pour des répliques du séïsme du Frioul.

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A Lithospheric Seismic Profile Along the Axis of the Alps; paper No. II.     

Eo-Alpine Metamorphism in the Uppermost Unit of the Cretan Nappe System — Petrology and Geochronology

The uppermost unit of the Cretan nappe system contains a variegated series of high-grade metamorphic rocks. In the Léndas area, amphibolites are present characterized by the assemblage

$$\text{brown}\;\text{hornblende}\;+\;\text{diopside}\;+\;\text{plagioclase}\;\text{(An 50)}$$

while associated metapelitic gneisses consist of

$$\text{garnet}\;+\;\text{cordierite}\;+\;\text{biotite}\;+\;\text{sillimanite (andalusite)}\;\pm\;\text{K-feldspar}\;+\;\text{plagioclase (An 40-50)}\;+\;\text{quartz}.$$

Judging from relevant experimental data for the gneiss assemblage including the Fe/Mg distribution on coexisting garnet and cordierite, the P-T conditions of metamorphism are estimated at about 700° C and 5 kb water vapour pressure.K/Ar determinations on hornblendes from three amphibolites yielded cooling ages of 71.3, 71.2, and 71.1 (±1.7) m.y. respectively; biotites from three paragneisses gave 70.2 ± 1.4, 69.7 ± 1.2, and 67.9 ± 1.4 m.y. respectively. Assuming a sealing temperature against argon diffusion of 300° C, for biotite, and 500° C, for hornblende, a cooling rate of 100–200° C/m.y. is calculated. Thus a late Cretaceous (eo-Alpine) metamorphic event is established in the post-Cretaceous nappes of Crete.     

Grundwasser der Zentralsahara: Fossile Vorräte

Zusammenfassung Aufgrund von¹⁴C-Datierungen, die an mehr als 40 Grundwasserproben aus Südlibyen vorgenommen wurden, wird nachgewiesen, daß die Grundwasservorräte des Murzuk-Beckens weitgehend fossil sind. Sie werden unter den gegenwärtigen klimatischen Bedingungen kaum ergänzt, was sehr wahrscheinlich ebenso auf den Hauptteil der Grundwasservorräte anderer Becken der Sahara zutrifft. Für die frühere Vorstellung, das Grundwasser werde in regenreicheren Gebirgen etwa der südlichen Sahara ausreichend ergänzt und fließe im Unterbau großflächig nach Norden, gibt es keine Hinweise. In Abhängigkeit vom ursprünglichen Ablagerungsmilieu und vom Speichergestein haben die Grundwässer der verschiedenen hydrogeologischen Teilprovinzen des Murzuk-Beckens jeweils spezifische hydrochemische Eigenschaften, und sie sind unterschiedlich alt. Als Ursache hierfür ist anzusehen, daß die Regenerationsmöglichkeiten innerhalb der verschiedenen Einzugsgebiete nicht immer einheitlich waren, außerdem kam es stellenweise zur Vermischung älterer mit jüngeren Grundwässern. Von erklärbaren Ausnahmen abgesehen entstammen die untersuchten Wässer dem letzten Pluvial, einige gehören nachpluvialen Feuchtphasen an. Das¹⁴C-Alter der meisten Wasserproben liegt zwischen 20 000 und 40 000 Jahren.

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¹⁴C-dating of more than 40 samples of groundwater proves, that exploited ground-water in the Murzuk Basin area of southern Libya is mainly between 20 000 and 40 000 years old. This water, as probably most of the large groundwater reserves in other Saharian basins, has to be considered mainly fossil water without noteworthy recharge under present climatical conditions. The supposition, that Saharian groundwaters are recharged at mountainous areas in the south, as was postulated by several authors previously, has to be denied, at least as respects the central Sahara.Waters of all groundwater subprovinces investigated in southern Libya show reservoir specific chemical characteristics. Differences in age are partly depending on differing recharge possibilities at the recharge areas and partly they are the result of mixture between younger and older waters. The water mainly results from precipitations of the last pluvial period of the Sahara, some from rainfalls of later subpluvial periods.

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Résumé Des datations par la méthode¹⁴C, effectuées sur plus de quarante échantillons d'eau provenant des nappes souterraines du Sud de la Libye, prouvent que les réserves des nappes souterraines du Bassin de Mourzouk sont essentiellement fossiles. Dans les conditions climatiques actuelles, elles ne peuvent pratiquement pas être complétées. Cette constatation concerne aussi, très vraisemblablement, la partie principale des réserves des nappes souterraines des autres bassins du Sahara. Aucune indication ne semble capable d'étayer les concepts antérieurs traitant d'une alimentation, encore suffisante aujourd'hui, de la nappe souterraine, coulant vers le Nord sur de grandes surfaces dans le sous-sol du Sahara, par les montagnes riches en pluies à peu près au Sud du Sahara.Les nappes souterraines des différentes parties des provinces hydrogéologiques du Bassin de Mourzouk possèdent, respectivement, des propriétés hydrochimiques spécifiques, dépendant du milieu de dépôt primitif et de la roche réservoir. Leurs distances variables jusqu'à l'ancienne aire d'alimentation et aussi sûrement, par endroit, le mélange imaginable d'eaux plus jeunes et plus vieilles causent, en partie, leurs différences d'âge.Les eaux étudiées, sauf quelques exceptions insignifiantes et faciles à expliquer, proviennent, d'une part des dernières grandes pluies, et d'autre part, pour quelques unes, des phases humides (post-pluviales). Elles ont, en grande partie, 20 000 à 40 000 ans.

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¹⁴ , 40 , Murzuk . - . , . , , . , , Murzuk , . . , . - . , . 20 000 40 000 .

     

Radon signals related to seismic activity in Ecuador,March 1987

A radon concentration measurement survey was carried out in Ecuador using the SSNTD technique. The data analysis shows a definite radon anomaly prior to March 6, 1987;M=6.9 earthquake. Anomalies found before October 18 and October 28th mild earthquakes in 1986 could be correlated with these events. Other anomalies that we cannot correlate with any geophysical event were also found.     

Late Quaternary barrier and fringing reef development of Bora Bora (Society Islands,south Pacific): First subsurface data from the Darwin‐type barrier‐reef system

The universally known subsidence theory of Darwin, based on Bora Bora as a model, was developed without information from the subsurface. To evaluate the influence of environmental factors on reef development, two traverses with three cores, each on the barrier and the fringing reefs of Bora Bora, were drilled and 34 uranium‐series dates obtained and subsequently analysed. Sea‐level rise and, to a lesser degree, subsidence were crucial for Holocene reef development in that they have created accommodation space and controlled reef architecture. Antecedent topography played a role as well, because the Holocene barrier reef is located on a Pleistocene barrier reef forming a topographic high. The pedestal of the fringing reef was Pleistocene soil and basalt. Barrier and fringing reefs developed contemporaneously during the Holocene. The occurrence of five coralgal assemblages indicates an upcore increase in wave energy. Age–depth plots suggest that barrier and fringing reefs have prograded during the Holocene. The Holocene fringing reef is up to 20 m thick and comprises coralgal and microbial reef sections and abundant unconsolidated sediment. Fringing reef growth started 8780 ± 50 yr bp ; accretion rates average 5·65 m kyr^?1. The barrier reef consists of >30 m thick Holocene coralgal and microbial successions. Holocene barrier‐reef growth began 10 030 ± 50 yr bp and accretion rates average 6·15 m kyr^?1. The underlying Pleistocene reef formed 116 900 ± 1100 yr bp , i.e. during marine isotope stage 5e. Based on Pleistocene age, depth and coralgal palaeobathymetry, the subsidence rate of Bora Bora was estimated to be 0·05 to 0·14 m kyr^?1. In addition to subsidence, reef development on shorter timescales like in the late Pleistocene and Holocene has been driven by glacioeustatic sea‐level changes causing alternations of periods of flooding and subaerial exposure. Comparisons with other oceanic barrier‐reef systems in Tahiti and Mayotte exhibit more differences than similarities.     

Zur Entwicklungsgeschichte der Südschwarzwälder Hauptbewegungszone (Devon-Karbon-Zug Badenweiler -Lenzkirch) während des Variscikums

In the Southern Black Forest area of SW-Germany, pre-Permian paleozoic sequences seem to be confined to a narrow strip around Badenweiler-Schönau-Lenzkirch. It consists of uncertain (possibly M.- to U.-Devonian) shales and “Kulm”, i.e. L.-Carboniferous greywackes, conglomerates, sandstones and shales with volcanic intercalations. The rocks can be subdivided in a) Tournai-greywackes of marine origin. Volcanism reaches into the b) Visé characterized by marine limestones and dolomites. There seems to be a disconformity above followed by c) conglomerates and pyroclastic rocks. A late-hercynian (variscean) tectonic out-line of the occurrence was initiated by early-variscean basin-formation.