Polymetamorphose und Deckenbau der Strand-Halbinsel/SW-Norwegen

Zusammenfassung Die Metamorphite der Halbinsel Strand / SW-Norwegen gehören zu einem Deckensystem präkambrischer Gesteine, das während der kaledonischen Orogenese von NNW her auf den Baltischen Schild geschoben worden ist (Sigmond Kildal 1978). Eine hangende Deckeneinheit umfa\t Metagranite, Melagabbroide und Gneise. Ihr granulitfazieller Mineralbestand (Metamorphosealter 1,5 Milliarden Jahre) wurde wahrscheinlich vor 1,18 Milliarden Jahren grünschieferfaziell retrograd überprägt. Die Decke ist nur noch in kleinen Erosionsinseln vorhanden. Eine liegende Dekkeneinheit besteht aus metasedimentären Gesteinen. Sie weist Mineralbestände der höheren Amphibolitfazies auf, die ebenfalls grünschieferfaziell überprägt wurden. Die Al^VI-Gehalte der bei beiden metamorphen Prozessen gebildeten Amphibole deuten bei Anwendung eines Diagramms vonRaase (1974) an, da\ die retrograde Metamorphose hier bei höheren Drücken ablief als die ältere Metamorphose. Ein Gesamtgesteinsalter von 1,16 Milliarden Jahren scheint für diese grünschieferfazielle Metamorphose das gleiche orogene Ereignis anzuzeigen wie für die hangende Einheit. Produkt der schwachen kaledonischen Metamorphose (400 Millionen Jahre) ist Stilpnomelan, der auch im Grundgebirge des Baltischen Schildes auftritt.

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The Strand Peninsula, Stavanger district, Southwestern Norway, has become well known, when V. M.Goldschmidt (1920) published his hypothesis of regional metasomatism. All rocks of the Strand area were assumed to be situated in autochthonous position. The main point ofGoldschmidt's hypothesis was progarde metamorphism of argillaceous sediments and their transformation to albite schists and plagioclase gneisses by metasomatic solutions given off from intruded trondhjemitic magmas.However, in contrast toGoldschmidt's ideas, the granitoid sill of the Ormakam-Moldhesten area, Strand Peninsula, and its wall rocks, which played an important role inGoldschmidt's discussion, are now found to be parts of a polymetamorphous thrust unit.Granulite facies assemblages, mainly consisting of orthopyroxene +clinopyroxene+plagioclase+hastingsite±orthoclase and quartz, have been partially replaced by lowgrade assemblages. Probably, the high-grade metamorphism has an age of about 1.5 Ga (Andresen &Heier 1975) whereas the age of the greenschist facies event may be conform to an orogenic cycle at about 1.15 Ga (Sigmond Kildal 1978).A lower nappe, covering the Strand Peninsula for its most parts, was subject of a petrologic re-examination using the microscope and the microprobe analyser. Its contacts with the hanging nappe as well as those with the underlying gneissic basement are characterized by thrust planes and horizons of phyllonites and cataclasites inside of the nappe and by local brecciation in the uppermost zones of the basement.The rocks of the lower nappe have been formed a long with the upper amphibolite facies as indicated by the following mineral assemblage: andesine + hastingsite and Mg-hornblende + quartz +biotite.Obviously, an inverse order of temperature regimes is recognizable in the allochthonous units. Maximum temperature of the upper nappe reached 800C (Müller &Herbert 1984) whereas T_max of the lower nappe did not exceed 750C.Using a diagram ofRaase (1974) the Al^VI-contents of the primary hastingsitic hornblendes of the lower nappe rocks indicate pressures which range distinctly below 5 kbars, whereas the secondary pargasitic hornblendes were formed at pressures of about 5 kbars. Probably the thrusting happened before the formation of secondary hornblendes took place. The load pressure in the lower nappe (< 5 kbars) was distinctly increased when the upper nappe was thrusted upon the lower one. Consequently the Al^VI-contents of secondary hornblendes indicate increased pressure ( 5 kbars).In the gneisses of the lower nappe late fractures were filled by stilpnomelane, chlorite and quartz. Very probably this depends on thrust movements during the Caledonian orogeny.Verschure et al. (1980) found a similar stilpnomelane formation in adjacent terrains of the basement and proposed a weak Caledonian metamorphism of about 400 my.

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Résumé Les roches métamorphiques de la presqu'Île de Strand (sud-ouest de la Norvège) appartiennent à un empilement de nappes formées de roches pré-cambriennes et charriées vers le SSE sur le bouclier baltique au cours de l'orogenèse calédonienne (Sigmond Kildal 1978).Une nappe supérieure comprend des métagranites, des mélagabbroÏdes et des gneiss. Leurs paragenèses, du facies des granulites (âge du métamorphisme: 1,5 Ga) ont été rétromorphosées dans le facies des schistes verts il y a probablement 1,18 Ga. Cette nappe ne subsiste qu'en petits fragments épargnés par l'érosion.Une nappe inférieure est composée de roches métasédimentaires. Ces roches présentent des paragenèses du faciès supérieur des amphibolites, également rétromorphosées dans le facies des schistes verts. L'application du diagramme de Raase (1974) aux teneurs en Al^VI des amphiboles formées lors des deux processus métamorphiques indique que la rétromorphose s'est déroulée à une pression supérieure à celle du métamorphisme ancien. Un âge de 1,16 Ga sur roche totale semble indiquer que le mÊme processus orogénique a servi de cadre à la rétromorphose en facies des schistes verts dans les deux nappes.Du stilpnomélane, présent tant dans la nappe inférieure que dans le bouclier baltique autochtone, témoigne d'un métamorphisme calédonien (400 Ma) de faible degré.

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Transmission electron microscopic study of antiphase domains in CaAl2Ge2O8-Feldspar

Transmission electron microscopic study of synthetic CaAl₂Ge₂O₈-feldspar revealed two types of antiphase domains: type “b”-antiphase domains with the displacement vector 1/2 [110] and type “c”-antiphase domains with the displacement vector 1/2 [111]. The “b”-domains were on the order of 0.1 μm in size, while the “c”-domains displayed wall to wall distances mostly between 0.1 and 1 μm. The formation of the two types of antiphase domains is due to reductions in translational symmetry associated with the phase transitions \(C\bar 1 \to I\bar 1 \to P\bar 1\) . The antiphase domain textures of CaAl₂Ge₂O₈-feldspar are very similar to the textures found in natural and synthetic anorthite, CaAl₂Si₂O₈.     

Eduard Suess' relations to the Pre-1950 schools of thought in global tectonics

Two main schools of thought in global tectonics are recognized during the first half of the XXth century on the basis of their proponents' attitude towards the principle of uniformitarianism and their belief in an inherent order and regularity vs. disorder and irregularity in tectonics. One group, here called the Wegener-Argand school, had a unifomitarian approach to global tectonics and believed in an inherently irregular Nature, in which probability rather than determinism was believed to be a realistic approach. The other, here called the Kober-Stille school, was largely non-uniformitarian (neocatastrophist) and believed in an orderly, regular Nature. These two schools correspond to Argand's mobilists and fixists respectively. In this paper I show that Eduard Suess was a convinced uniformitarian as far as his views on global tectonics are concerned and denied any inherent regularity in tectonic phenomena, temporal or spatial. In his interpretations of the causes and nature of orogeny, nature of geosynclines, and causes and nature of stabilisation, Suess appears to be the predecessor of the Wegener-Argandians, i. e. of the mobilists and not of the Kober-Stilleans as hitherto assumed. Although he remained a fixist and contractionist to the end Suess seems to have paved the way for the mobilists much as he did for the nappists during the last quarter of the XIX^th century.

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Zusammenfassung Während der ersten Hälfte des XX. Jahrhunderts kann man zwei globaltektonische Denkungsweisen oder Großschulen unterscheiden, die gekennzeichnet sind durch ihre Stellungnahme zum aktualistischen Prinzip in der Tektonik und ob sie an eine ordentliche und regelmäßige Natur glaubten oder nicht. Die erste, hier die Wegener-Argand-Schule genannt, hatte die Gültigkeit des aktualistischen Prinzips in der Tektonik anerkannt und die Natur, im Grunde genommen, als unordentlich und unregelmäßig betrachtet. Die Anhänger dieser Denkweise glaubten, daß probablistische Lösungen tektonischer Probleme realistischer seien als deterministische. Die andere Großschule, hier die Kober-Stille-Schule genannt, war im Grunde genommen anti-aktualistisch (Neo-Katastrophistisch) und glaubte, daß die Natur ordentlich und regelmäßig sei. Diese zwei Schulen entsprechen Argands' Einteilung in Mobilisten und Fixisten. In diesem Artikel zeige ich, daß E. Suess ein überzeugter Aktualist in bezug auf seine tektonischen Ansichten war, und daß er jede Regelmäßigkeit, zeitlicher oder räumlicher Art, der tektonischen Ereignisse ablehnte. In seinen Interpretationen der Ursachen und der Art der Orogenese, der Art der Geosynklinalen und der Ursache und der Art der Erstarrung, erscheint Suess als ein Vorgänger der Wegener-Argand-Schule, d. h. der Mobilisten, deren Gedankengänge er viel näher stand als dem der Kober-Stille-Schule. Obwohl Suess selbst bis zuletzt ein Fixist und Kontraktionist blieb, bereitete er eigentlich den Weg für die Mobilisten, wie er es früher auch für die Nappisten getan hatte.

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Résumé Durant la première moitié du XX^e siêcle, on peut distinguer deux principales écoles de pensée en tectonique globale, selon l'attitude de ses adhérents envers le principe de l'actualisme et selon leur croyance ou non à un ordre et une régularité intrinsèques en tectonique. Le premier groupe, ici appelé l'école de Wegener-Argand, suivit une voie actualiste et crût la Nature essentiellement irrégulière, de telle sorte qu'un traitement probabiliste fût considéré plus réaliste qu'un traitement déterministe. L'autre, appelé ici l'école de Kober-Stille, était essentiellement non-actualiste (néo-catastrophiste) et crût à une Nature ordonnée, régulière. Ces deux écoles correspondent aux mobilistes et aux fixistes d'Argand. Dans cet article, je montre que E. Suess, fût un actualiste convaincu, du moins en ce qui concerne ses opinions sur la tectonique globale, et qu'il rejetta toute notion de régularité dans les phénomènes tectoniques, autant spatiaux que temporaux. Dans ses interprétations des causes et de la nature de l'orogenèse, de la nature des géosynclinaux, et des causes et de la nature de la «stabilisation», Suess est un des précurseurs des «Wegener-Argandiens», c'est à dire des mobilistes. Bien qui'il fût demeuré, jusqu'à la fin de sa vie, fixiste et un avocat de la contraction, il semble que Suess ait préparé la voie aux mobilistes, de la mème façon qu'il l'avait fait pour les nappistes pendant le derier quart du XIX^e siècle.

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Kulkeite,a new metamorphic phyllosilicate mineral: Ordered 1∶1 chlorite/talc mixed-layer

Kulkeite occurs as platy, colorless, porphyroblastic, single crystals up to 2 mm in size in a low-grade dolomite rock associated with a Triassic meta-evaporite series at Derrag, Tell Atlas, Algeria, It is associated with sodian aluminian talc, unusual chlorite polytypes, and both K and Na phlogopite. Kulkeite is optically biaxial, negative, n _x=1.552, n _y=1.5605, n _z=1.5610, 2V_z=24° (obs.). Based on microprobe analysis the empirical formula is (Na_0.38K_0.01Ca_0.01)(Mg_8.02Al_0.99)[Al_1.43Si_6.57O₂₀](OH)₁₀ with some variation in Na, Si, and tetrahedral Al. The crystals are monoclinic with a=5.319(1), b=9.195(2), c=23.897(10) Å, β=97° 1(3)′; Z=2; the calculated density is 2.70 g cm^?3. The four strongest lines in the X-ray powder pattern are (d, I, hkl): 7.90, 100, 003; 1.533, 100, 060; 7.42, 80, 002; 3.38, 80, 007; the 001 reflection with 23.7 Å has intensity 10. Transmission electron microscopy confirms the nature of a regular 1∶1 mixed-layer, which consists of 14 Å chlorite (clinochlore) sheets alternating with sheets of one-layer (9.5 Å) talc characterized by the lattice substitution NaAl→Si just as in the talc occurring as a discrete mineral co-existing with kulkeite. Kulkeite is intergrown with lamellae of clinochlore that represent two-layer and five-layer (70 Å) polytypes with optical birefringence exceeding the normal value for clinochlore by a factor of 3. The origin of kulkeite is due to low-grade metamorphism with temperatures probably not exceeding 400° C. As the clinochlore lamellae and sodian aluminian talc are found in mutual contact, kulkeite seems to represent a metastable mineral at least during the latest phase of metamorphism. However, at an earlier stage, prior to clinochlore formation, kulkeite might have been stable, and the incorporation of Na and Al into its talc component could indeed be the decisive factor for the formation of the mixed-layer.     

Polymetamorphic relations in iron ores from the Iron Quadrangle,Brazil: The correlation of oxygen isotope variations with deformation history

This study deals with the oxygen isotope composition of hematite-rich ore bodies in the Iron Quadrangle, Brazil. The area studied can be divided into two different regions: a western (W) zone of greenschist facies assemblages and an eastern (E) zone of amphibolite facies with transitions into granulite facies assemblages.The ¹⁸O values of 136 quartz-iron oxide pairs have been determined and temperatures of formation have been calculated. The ¹⁸O values of quartz vary between +6 and 20 except one value near +23, whereas the iron oxides fall between –4 and +10, with nearly 80% of the iron oxide values between –0.5 and 4.0. The regional distribution of the ¹⁸O values is as follows: in the W-region 85% of the quartz are >12, whereas in the E-region only 46% fall in this range, In contrast to quartz the iron oxides do not show any regional differences.The variation of oxygen isotope fractionations between quartz and iron oxides is obviously related to the complex deformation history of the iron ores. Samples with a primary schistosity (S₁) only represent peak metamorphic conditions. In the E-region the (S₁) high temperatures >700° C seem to correspond to orogenic events in the Archaen basement 2,700 m.y. ago. In the W-region S₁-temperatures between 460° and 560° C seem to represent peak metamorphic conditions of the Proterozoic Minas metamorphism 2,000 m.y. ago. Iron ores which have been overprinted by later deformation events are selectively reset to lower isotopic temperatures. The more closely spaced the schistosity planes the larger the extent of a temperature lowering.The genetic processes associated with these hematite-rich ore bodies appear to be sedimentary-metamorphic rather than metasomatic processes. Furthermore, there is no evidence for secondary leaching by weathering solutions.     

Orientation of the stress field from breakouts in a crystalline well in a seismic active area

The orientation of the regional stress field in the Swabian Jura was determined from borehole breakouts caused by stress accumulation at the borehole wall. The analysis is based on caliper data recorded in the Urach 3 geothermal well within an intervall of about 1450 m. The azimuths of the breakouts are consistent with depth and indicate a stress direction which is in good agreement with the interpretation of fault plane solutions of nearby earthquakes.     

Mögliche Massnahmen zur Restaurierung des Sempachersees

Since 1954 average orthophosphate and total phosphorus concentrations have increased twenty and eightfold respectively in Lake Sempach. It is demonstrated that the lake is not in steady state with its phosphorus loading and that the net deposition rate of phosphorus is not linearly related to the phosphorus content of the lake. This implies that linear steady state one-box models are unsuitable to describe the phosphorus balance of this lake. Applying a nonlinear dynamic lake model we predict that the defined water quality goals ([P] ⩽30 mg m⁻³, [O₂ ⩾4 mg m⁻³]) can only be achieved within the next 15 years if the external phosphorus loading is reduced by at least 50% and simultaneously lake-internal measures, such as hypolimnion areation or hypolimnion siphoning are carried into effect.      

Fission tracks in minerals: Annealing kinetics,track structure and age correction

It is shown that the annealing kinetics of fission tracks in apatite can be described by a sum of exponential decay functions. From an analysis of the temperature dependence of this annealing law it is concluded that the etchability of fission tracks is due to extended defects, i.e. systems of dislocation loops. The multiexponential annealing law is also applied to prove that the plateau correction method is basically correct, but rather as a method for determining a lower limit than the “true” fission track age.