Formation of Mud-Volcanic Fluids in Taman (Russia) and Kakhetia (Georgia): Evidence from Boron Isotopes

Temperatures of the formation of mud-volcanic waters are determined based on concentrations of some temperature-dependent components (Na–Li, Mg–Li). Estimates obtained for the Taman and Kakhetia regions are similar and range from 45 to 170°, which correspond to depths of 1–4.5 km. The calculated temperatures correlate with the chemical (Li, Rb, Cs, Sr, Ba, B, I, and HCO₃) composition of water and ¹³ (₂) and ¹³ (CH₄) values in spontaneous gases. The isotope values indicate that mechanisms of the formation of ¹³-rich gases, i.e., gases with high ¹³ values (up to +16.0 in ₂ and –23.4 in CH₄) in mud-volcanic systems of Taman and Kakhetia are governed by fluid-generation temperatures rather than the supply of abyssal gases. The ¹¹ value was determined for the first time in mud-volcanic products of the Caucasus region. This value ranges from +22.5 to +39.4 in the volcanic water of Georgia, from –1.2 to +7.4 in the clayey pulp of Georgia, and from –7.6 to +13.2 in the clayey pulp of Taman. It is shown that the ¹¹ value in clay correlates with the fluid-generation temperature and ¹¹ correlates with ¹³ in carbon-bearing gases. These correlations probably testify to the formation of different phases of mud-volcanic emanations in a single geochemical system and suggest the crucial role of temperature in the development of isotope-geochemical features.     

Isotopic composition of oxygen and hydrogen in mud-volcanic waters from Taman (Russia) and Kakhetia (Eastern Georgia)

The ¹⁸O and D values in mud-volcanic waters of the Taman Peninsula and Kakhetia vary from +0.7 to +10.0 and from –37 to –13 , respectively. These values increase as the Greater Caucasus is approached. The increase in 18O and D also positively correlates with fluid generation temperatures based on hydrochemical geothermometers. This is accompanied by changes in the chemical composition of waters, in which contents of alkali metals, HCO^– ₃ ion, and boron increase, while the content of halogen ions (Cl, Br, J) decreases. Changes in the isotopic composition of water are also accompanied by the increase of ¹³ in methane and decrease of ¹¹ B in clays. Analysis of formal models of the evolution of isotopic composition of mud-volcanic waters showed that mud volcanoes are recharged by freshened water from the Maikop paleobasin with an inferred isotopic composition of D –40 and ¹⁸ O –6. Based on this assumption, the ¹⁸O and D values observed in mud-volcanic waters can be explained not only by processes of distillation and condensation in a closed system, but also by combined processes of isotopic reequilibration in the water-illite-methane system.Translated from Litologiya i Poleznye Iskopaemye, No. 2, 2005, pp. 143–158.Original Russian Text Copyright © 2005 by Lavrushin, Dubinina, Avdeenko.     

Modification of δD values in eastern Nevada granitoid rocks spatially related to thrust faults

Stable isotope data have been determined for 13 Mesozoic and Tertiary plutons in eastern Nevada and nearby Utah. In the southern Snake Range of eastern Nevada, where relations are best exposed and have been most intensively studied, D, ¹⁸O, and apparent K-Ar ages depend on proximity to the Snake Range decollement. Where stresses resulting from late movement on the decollement have caused cataclasis of Oligocene (37 Ma) granitoid rock, ¹⁸O, D, and K-Ar age values as low as –2.5, –155, and 18 Ma, respectively, have been determined. Where there has been no cataclasis, ¹⁸O values of Jurassic, Cretaceous, and Oligocene granitoid rocks are apparently unaffected, but both D values and K-Ar ages have been modified for distances of tens of meters below the decollement.Results similar to those in the southern Snake Range have been observed in other eastern Nevada granitoid rocks spatially related to regional thrust faults, as in the Kern Mountains, the Toana Range, and the northern Egan Range. In each of these areas cataclasis or deformation of granitoid rocks has resulted in lowered ¹⁸O, D, and K-Ar age values. Where there has been no cataclasis or deformation, ¹⁸O values are unaffected, but both D and K-Ar age values have been lowered by stresses resulting from postcrystallization movement along overlying thrust faults.Many of the plutons discussed have not been deeply eroded, and spatially related thrust faults crop out. Where thrust faults are not in evidence and the granitoid rocks give D values lower than about –130 along with spuriously low K-Ar age results, modification of the D and K-Ar age values may have been caused by stresses related to late movement along an overlying (now eroded) thrust fault.     

Sulphur and sulphate-oxygen isotopes and the origin of the silvermines deposits,Ireland

New sulphur and sulphate-oxygen isotope measurements for the main discordant and stratiform lead-zinc-barite orebodies at Silvermines Co. Tipperary, allow reappraisal of previously offered differing interpretations (Graham, 1970; Greig et al., 1971) of the bearing of sulphur isotopes on the genesis of this important Irish deposit. The following aspects of the data are confirmed: barite ³⁴ S-values range from 17–21, similar to lower Carboniferous seawater sulphate: stratiform sulphide lens pyrites have ³⁴ S-values ranging from –13 to –36; vein sulphide ³⁴ S-values range from –8 to 4; sulphide ³⁴ S-values increase upwards and outwards respectively in the related discordant and stratiform G orebodies; galena-sphalerite isotope palaeotemperatures are not too consistent, ranging from 40 to 430°C (using the calibration of Czamanske and Rye (1974). New facts are as follows: barite ¹⁸O-values range from –13 to –17, stratiform barites ranging from 13 to 14.5; sulphides separated from a single stratiform ore lens hand specimen usually have ³⁴ S_sl > ³⁴ S_ga > ³⁴ S_py; the outward decrease in ³⁴ S-values in the stratiform G orebody is confined to the first few hundred feet only; pyrite ³⁴ S-values progressively increase downwards through one stratiform sulphide orebody; yet variations of 13 occur within a single colloform pyrite structure from another stratiform orebody. It is concluded that there were at least two sources of sulphur, seawater sulphate and deep-seated sulphur. The former was the dominant source of all sulphate and, via biogenic reduction, of the sulphur in the bulk of the stratiform sulphide. The latter was the source of the sulphur in the vein sulphides. There was minimal isotopic interaction between the cool seawater sulphate and the warm unwelling ore fluid sulphur species, even though the latter precipitated under near isotopic equilibrium conditions when the temperature dropped and/or the pH and Eh increased. The lack of isotopic equilibrium between pyrite and ore sulphides in the stratiform ore lenses may result from the latter having precipitated slightly later than the former because of solubility relationships. Overall the present isotopic evidence supports considerable geological evidence favoring a syngenetic origin for the stratiform Silvermines orebodies.     

Changes in stable isotope ratios of metapelites and marbles during regional metamorphism,Mount Lofty Ranges,South Australia: implications for crustal scale fluid flow

The Mount Lofty Ranges comprises interlayered marbles, metapsammites, and metapelites that underwent regional metamorphism during the Delamarian Orogeny at 470–515 Ma. Peak metamorphic conditions increased from lowermost biotite grade (350–400°C) to migmatite grade (700°C) over 50–55 km parallel to the lithological strike of the rocks. With increasing metamorphic grade, ¹⁸O values of normal metapelites decrease from 14–16 to as low as 9.0, while ¹⁸O values of calcite in normal marbles decrease from 22–24 to as low as 13.2 These isotopic changes are far greater than can be accounted for by devolatilisation, implying widespread fluid-rock interaction. Contact metamorphism appears not to have affected the terrain, suggesting that fluid flow occurred during regional metamorphism. Down-temperature fluid flow from synmetamorphic granite plutons (¹⁸O=8.4–8.6) that occur at the highest metamorphic grades is unlikely to explain the resetting of oxygen isotopes because: (a) there is a paucity of skarns at granite-metasediment contacts; (b) the marbles generally do not contain low-XCO₂ mineral assemblages; (c) there is insufficient granite to provide the required volumes of water; (d) the marbles and metapelites retain a several permil difference in ¹⁸O values, even at high metamorphic grades. The oxygen isotope resetting may be accounted for by along-strike up-temperature fluid flow during regional metamorphism with time-integrated fluid fluxes of up to 5x10⁹ moles/m² (10⁵ m³/m²). If fluid flow occurred over 10⁵–10⁶ years, estimated intrinsic permeabilities are 10^-20 to 10^-16m². Variations in ¹⁸O at individual outcrops suggest that time-integrated fluid fluxes and intrinsic permeabilities may locally have varied by at least an order of magnitude. A general increase in XCO₂ values of marble assemblages with metamorphic grade is also consistent with the up-temperature fluid-flow model. Fluids in the metapelites may have been derived from these rocks by devolatilisation at low metamorphic grades; however, fluids in the marbles were probably derived in part from the surrounding siliceous rocks. The marble-metapelite boundaries preserve steep gradients in both ¹⁸O and XCO₂ values, suggesting that across-strike fluid fluxes were much lower than those parallel to strike. Up-temperature fluid flow may also have formed orthoamphibole rocks and caused melting of the metapelites at high grades.This paper is a contribution to IGCP Project 304 Lower Crustal Processes     

Sulfur isotope ratios of Icelandic rocks

Sulfur isotope ratios have been determined in 27 selected volcanic rocks from Iceland together with their whole rock chemistry. The ³⁴S of analyzed basalts ranges from –2.0 to +0.4 with an average value of –0.8 Tholeiitic and alkaline rocks exhibit little difference in ³⁴S values but the intermediate and acid rocks analyzed have higher ³⁴S values up to +4.2 It is suggested that the overall variation in sulfur isotope composition of the basalts is caused by degassing. The small range of the ³⁴S values and its similarity to other oceanic and continental basalts, suggest that the depleted mantle is homogeneous in its sulfur isotope composition. The ³⁴S of the depleted mantle is estimated to be within the range for undegassed oceanic basalts, –0.5 to +1.0     

The brittle-plastic transition and the depth of seismic faulting

A simple rheological model of shearing of the lithosphere that has gained wide acceptance is a two layer model with an upper brittle zone in which deformation takes place by frictional sliding on discrete fault surfaces and a lower plastic zone in which deformation takes place by bulk plastic flow. The two are separated by an abrupt brittle-plastic transition, which is assumed to be indicated by the lower limit of seismicity. Experimental studies, however, as well as the deformation structures of mylonites, indicate that a broad transitional field of semi-brittle behavior lies between these extremes. This is a field of mixed mode deformation with a strength that can be expected to be considerably higher than that predicted from the extrapolation of high temperature flow laws. For quartzofeldspathic rocks the semi-brittle field lies between T₁, the onset of quartz plasticity at about 300 °C and T₂, feldspar plasticity at about 450 °C. A model is presented in which the transition T₁ does not correspond to a transition to bulk flow but to a change from unstable, velocity-weakening friction to stable, velocity-strengthening friction. T₁ thus marks the depth limit of earthquake nucleation, but large earthquakes can propagate to a greater depth, T₃, (T₃2) which corresponds to the lower limit of dynamic frictional behavior in the semi-brittle field and approximately to the peak in strength. The zone between T₁ and T₃ is one of alternating behavior, with flow occurring m the interseismic period and with co-seismic dynamic slip occurring during large earthquakes. This zone is characterized by mylonites interlaced by pseudotachylytes and other signs of dynamic faulting. The transition T₁ is also marked by a change in the generation mechanism of fault rocks, from abrasive wear above which produces cataclastites, to adhesive wear below, which is proposed as an important generation mechanism of mylonites in the upper part of the semi-brittle field.

---

Zusammenfassung Ein einfaches rheologisches Modell für Schervorgänge in der Lithosphäre, das eine weite Akzeptanz erreicht hat, ist das Zweilagenmodell mit einer oberen spröden Zone, in der Deformation über Reibungsgleitung entlang diskreter Störungsflächen stattfindet, und einer unteren duktilen Zone. Hier erfolgt die Deformation durch plastisches Fließen. Beide Zonen werden durch einen abrupten spröd-plastischen Übergang voneinander getrennt, der vermutlich durch die untere Grenze der nachweisbaren Seismizität angezeigt wird. Experimentelle Untersuchungen wie auch die Deformationsgefüge in Myloniten zeigen hingegen, daß ein breites Übergangsfeld mit semisprödem Verhalten zwischen diesen beiden Extremen liegt. Hier befindet sich ein Bereich »gemischter« Deformation, deren Ausmaß beträchtlich über den aus der Extrapolation von Hochtemperatur-Fließ-Gesetzmäßigkeiten ableitbaren Werten liegen dürfte. Für Quarz-Feldspat-Gesteine liegt das halbspröde Feld zwischen T₁ dem Beginn der plastischen Deformation des Quarzes bei ca. 300 °C, und T₂, dem Beginn der Feldspatplastizität bei ca. 450 °C. Hier wird ein Modell vorgestellt, in dem der Übergang bei T₁ nicht dem Übergang zum Gesamtfließen, sondern dem Wechsel von instabiler, geschwindigkeitsreduzierender Reibung zu stabiler, geschwindigkeitskonstanter Reibung entspricht. T₁ markiert damit die Tiefengrenze der Erdbebenbildung, stärkere Beben können dagegen in größere Tiefe reichen T₃ (T₃2), die dann der unteren Grenze dynamischen Reibungsverhaltens im semispröden Bereich und angenähert dem Stärkemaximum entspricht. Die Zone zwischen T₁ und T₃ zeigt alternierendes Verhalten mit plastischem Fließen während interseismischer Perioden und dynamischem Gleiten während größerer Erdbeben. Diese Zone wird charakterisiert durch Mylonite und dicht zwischengepackten Pseudotachyliten sowie anderen Anzeigern dynamischer Faltung. Hinzu kommt im Bereich des Überganges T₁ ein Wechsel im Bildungsmechanismus gestörter Gesteine. Er geht von durchgreifender Ermüdung, die zu Kataklasiten führt, bis zu adhesiver Ermüdung, die als wichtiger Bildungsmechanismus für Mylonite im oberen Abschnitt des semispröden Feldes angesehen wird.

---

Résumé Le modèle rhéologique de cisaillement de la lithosphère le plus largement accepté comporte deux couches superposées: une couche supérieure cassante, siège de déformations le long de surfaces discrètes, les failles, et une zone inférieure ductile ou s'opère un fluage plastique d'ensemble. La transition entre ces deux domaines est brusque et considérée comme la limite inférieure de la séismicité.L'étude des structures mylonitiques ainsi que les mesures expérimentales indiquent cependant qu'un large champ de transition à caractère «semi-cassant» s'étend entre ces deux extrêmes. Ruptures et fluage plastique sont présents dans cette zone, dont la compétence peut être considérée comme bien supérieure à celle qui résulte de l'extrapolation des lois de fluage à haute température. Pour les roches quartzofeldspathiques, ce champ «semi-cassant» s'étend de T₁, seuil de plasticité du quartz (environ 300 °C) à T₂, celui du feldspath (environ 450 °C). Dans ce modèle, la température T₁ ne correspond pas au seuil de fluage d'ensemble, mais à la frontière entre une région de frictions «instables» qui diminuent avec la vitesse, et une région de frictions «stables» qui augmentent avec la vitesse. Elle correspond donc à la profondeur limite de genèse des séismes. Les grands séismes peuvent cependant se propager jusqu'à une profondeur T₃ (T₃2) qui correspond à la limite inférieure du comportement dynamique des forces de frottement dans le domaine «semicassant». T₃ peut être considérée approximativement comme le point de résistance maximale de cette zone de transition. La zone comprise entre T₁ et T₃ peut donc être le siège alternativement soit de processus de fluage, soit de glissements le long de surfaces de rupture à l'occasion de séismes de forte magnitude. Cette zone se caractérise par des mylonites entremêlées de pseudotachylites et autres signes de rupture dynamique. La transition T₁ est également marquée par une modification du mécanisme de transformation des roches dans les zones de faille. Audessus de cette limite, un mécanisme d'usure «abrasif» produit des cataclasites, par opposition à un mécanisme d'usure «adhésif» en-dessous. Ce dernier mécanisme est proposé comme fort probable lors de la genèse de mylomtes dans la partie supérieure du champ «semi-cassant».

---

() , . , , . . - , , . , , , , , . « » , , . - T₁ — 300° T₂ — 450°. , T₁ , , , . . . T₁ , , . — ₃ (₃ > ₂), . . , . t_{1 2} . , . , t₁ . , , ; .

     

Contrasting fluid flow patterns at the Bufa del Diente contact metamorphic aureole,north-east Mexico: evidence from stable isotopes

Impure limestones with interstratified metachert layers were contact metamorphosed and metasomatized by the Bufa del Diente alkali syenite. Massive marbles exhibit mineralogical and stable isotope evidence for limited fluid infiltration, confined to a 17 m wide zone at the contact. Influx of magmatic brines along most metacherts produced up to 4 cm thick wollastonite rims, according to calcite (Cc)+quartz (Qz)= wollastonite (Wo)+CO₂, and were observed at distances of up to 400 m from the contact. The produced CO₂ exsolved as an immiscible low density CO₂-rich fluid. Chert protolith isotope compositions were ¹⁸O (Qz)=27–30%. and ¹⁸O (Cc)=24–27%.. Many wollastonites in infiltrated metacherts have low ¹⁸O ranging from 11–17 and confirm that decarbonation occurred in presence of a magmatic-signatured fluid. Large gradients in ¹⁸O (Wo) across the rims may reach 6 The ¹⁸O of remaining quartz is often lowered to 15–20 whereas caleites largely retained their original compositions. The isotopic reversals of up to 10 between quartz and calcite along with reaction textures demonstrate non-equilibrium between infiltrating fluid in the aquifer and the assemblage calcite+quartz+wollastonite. This is compatible with the assumption of a down-temperature flow of magmatic fluids that occurred exclusively in the remaining quarzite layer. The ¹³C (Cc) and ¹⁸O (Cc) of marble calcites measured perpendicular to two metachert bands reveal significant isotopic alterations along distances of 4.5 cm and 7.5 cm from the wollastonite-marble boundary only into the hanging wall marble, suggesting an advection process caused by a fluid phase which movel upwards. Covariation trends of ¹³C (Cc) and ¹⁸O (Cc) across the alteration front indicate that this fluid was CO₂-rich. Mass balance calculations show that all CO₂-rich fluid produced by the decarbonation reaction was lost into overlying marble. The metachert aquifers did not leak with respect to water-rich fluids.     

Rb-Sr evidence for the presence of Ordovician gsranites in the deformed basement of the Badajoz-Córdoba belt,SW Spain

A Rb-Sr whole-rock investigation of suites of samples from two orthogneiss bodies in the Almendralejo area of the Oporto-Portalegre-Badajoz-Córdoba belt points to an Ordovician age for the granitic magmatism: about 470 Ma for the Almendralejo Gneiss (peralkaline metagranite) and about 425 Ma for the Ribera del Fresno Gneiss (leucocratic subaluminous metagranite), both with high initial⁸⁷Sr/⁸⁶Sr ratios. This points to a post-Ordovician (Hercynian) age for the metamorphism and tectonic deformation that affected the area, including the gneisses, and rules out the alleged Cadomian or even older age.

---

Zusammenfassung Die Rb-Sr-Gesamtgesteinsanalysen von Probeserien zweier orthogneisischer Körper der Almendralejo-Region des Oporto-Portalegre-Badajoz-Córdoba-Gürtels weisen auf ein ordovizisches Alter des granitischen Magmas hin: rund 470 Ma für den Almendralejo-Gneis (peralkaliner Metagranit) und rund 425 Ma für den Ribera del Fresno-Gneis (leukokratischer Metagranit), beide bei einem hohen initialen⁸⁷Sr/⁸⁶Sr. Diese Ergebnisse deuten auf ein post-ordovizisches (herzynisches) Alter der Metamorphose und der tektonischen Deformation hin, die das Gebiet, einschließ-lich des Gneises, beeinflußt haben. Sie schließen ein vermeintliches kadomisches oder älteres Alter aus.

---

Résumé Une étude par Rb-Sr sur roche totale de séries d'échantillons de deux massifs d'orthogneiss de la région d'Almendralejo, dans la ceinture Oporto-Portalegre-Badajoz-Cordoue, indique un âge ordovicien pour le magmatisme granitique: environ 470 Ma pour le gneiss d'Almendralejo (métagranite peralcalin) et environ 425 Ma pour le gneiss de Ribera del Fresno (métagranite leucocrate subalumineux), tous deux avec des rapports initiaux⁸⁷Sr/⁸⁶Sr élevés. Ces résultats indiquent un âge post-ordovicien (hercynien) pour le métamorphisme et la déformation tectonique qui ont affecté la région, y compris les gneiss, et éliminent l'hypothèse proposée par ailleurs d'un âge cadomien ou même plus ancien.

---

— — — Rb/Sr : 425 -- ( ) 470 ( ) ⁸⁷Sr/⁸⁶Sr . - ( ) , , . , .

     

Contrasting serpentinization processes in the eastern Central Alps

Stable isotope compositions have been determined for serpentinites from between Davos (Arosa-Platta nappe, Switzerland) and the Valmalenco (Italy). D and ¹⁸O values (–120 to –60 and 6–10, respectively) in the Arosa-Platta nappe indicate that serpentinization took place on the continent at relatively low temperatures in the presence of limited amounts of metamorphic fluids that contained a component of meteoric water. One sample of chrysotile has a ¹⁸O value of 13 providing evidence of high W/R ratios and low formation temperature of lizardite-chrysotile in this area. In contrast, relatively high D values (–42 to –34) and low ¹⁸O values (4.4–7.4) for serpentine in the eastern part of the Valmalenco suggest a serpentinization process that took place at moderate temperatures in fluids that were dominated by ocean water. The antigorite in the Valmalenco is the first reported example of continental antigorite with an ocean water signature. An amphibole sample from a metasomatically overprinted contact zone to metasediments (D=-36) indicates that the metasomatic event also took place in the presence of ocean water. Lower D values (–93 to –60) of serpentines in the western part of the Valmalenco suggest a different alteration history possibly influenced by fluids associated with contact metamorphism. Low water/rock ratios during regional metamorphism (and metasomatism) have to be assumed for both regions.     

Isotopic Composition of Oxygen and Carbon and Formation Temperature of Accessory Minerals from Evaporitic Sediments in the Pripyat Trough

The isotopic composition of oxygen and carbon was studied in accessory carbonates and quartz separated from salts in Upper Devonian halogenous formations of the Pripyat Trough (Belorus). It is established that isotopic characteristics vary in a wide range. Values of ¹⁸O vary in the following range (SMOW): from 18.2 to 29.2 in calcites, from 15.7 to 32.5 in dolomites, and from 17.4 to 27.2 in quartz. Values of ¹³C range from –13.4 to 1.4 in calcites and from –11.1 to 1.7 in dolomites (PDB). Results obtained indicate highly variable isotope-geochemical conditions of sedimentation and early diagenesis during the formation of evaporitic sediments. Accessory minerals were repeatedly formed in a wide temperature range and probably at various stages of the lithogenesis.     

Sulfur isotopes and origin of some sulfide deposits,New England,Australia

The S-isotopic compositions of sulfide deposits from Steinmann, granitoid and felsic volcanic associations have been examined. Ores of Steinmann association have ³⁴S values close to zero per mil (³⁴S=+0.3±3.1) it appears they are of mantle origin. Isotopically, ores of granitoid association regularly show a variable enrichment in ³²S relative to meteoritic (³⁴S=–2.7±3.3). The composition is in accord with an upper mantle/lower crustal source. Two stratiform accumulations of felsic volcanic association show a narrow spread of ³⁴S values (+0.2 to 2.4); a mantle origin for the sulfur in these deposits is favored. In contrast, vein, stockwork and cement ores are moderately enriched in ³²S relative to meteoritic (³⁴S=–4.0±6.4). These ores are polygenetic; sulfur and metals appear to have been leached from local country rocks where volcanogenic and biogenic sulfur predominate.     

Meteoric hydrothermal origin of calcites in “Green Tuff” formations,Miocene age,Japan

Oxygen and carbon isotope compositions were determined for calcites from the Green Tuff formations of Miocene age in Japan. Values of ¹⁸O from 24 calcites in altered rocks from 5 districts range from –2 to +16_SMOW, in most cases from 0 to +8_SMOW. The low ¹⁸O values rule out the possibility of their low-temperature origin or any significant contribution of magmatic fluid in the calcite precipitation. These values, coupled with their mineral assemblages, suggest that the calcites formed from meteoric hydrothermal solutions which caused propylitic alteration after the submarine strata became emergent.Values of ¹³C from the calcites show a wide variation from –17 to 0_PDB. Calcites from different districts have different ranges of ¹³C values, indicating that there was no homogeneous reservoir of carbon at the time the calcite formed, and that the carbon had local sources. Carbon isotopic compositions of calcite within ore deposits in the Green Tuff formations range from –19 to 0_PDB, similar to those of calcite in the altered rocks in the same district, suggesting that the carbon in ore calcites was likely supplied from the surrounding rocks through activity of meteoric hydrothermal solutions.     

Die fazielle und paläogeographische Entwicklung im Perm der Karnischen Alpen und in den Randgebieten

Zusammenfassung Im Unterperm bildet sich mit den küstennahen Innenschelf-Sedimenten der Unteren Pseudoschwagerinen-Kalke (UPK) und über der klastischen Fazies der im hochenergetischen Intertidal-Subtidal-Grenzbereich entstandenen Grenzlandbänke (GB) die Karbonatplattform der Oberen Pseudoschwagerinen-Kalke (OPK) heraus. Ökologische Zonenfolgen, die eine zunehmende Verschiebung zu küstenferneren Bereichen anzeigen, weisen die OPK als Ablagerungen des subtidalen Außenschelf-Bereiches aus.Verschieden alte Schelfrandriffe (Karnische Alpen, Sextener Dolomiten) und die Klastischen Trogkofelschichten als Innenschelfentwicklung im E und SE setzen die Entwicklung der Plattform in der Trogkofelstufe fort.Bodenunruhen mit Brekzienbildungen in den Klastischen Trogkofelschichten gipfeln in einem Zerbrechen der Karbonatplattform an der Wende Unter/Mittelperm und führen zur Ablagerung der Tarviser Brekzie in lokalen Senken.Mit den im W zunächst noch kontinentalen, in den Karnischen Alpen und Westkarawanken aber überwiegend marinen Grödener Schichten und den bei fortschreitender Transgression abgelagerten Bellerophonschichten setzt der alpidische Sedimentationszyklus ein.

---

Paleontological and sedimentological data of Permian rocks from the Carnic Alps and its neighbouring areas south of the Periadriatic Lineament could fit to the following paleogeographical patterns:The Untere Pseudoschwagerinen-Kalke (UPK) of the Rattendorfer Schichten were cyclically deposited in the inner-shelf area. During the upper UPK erosive activities and source areas of the clastics were changing. Increasing sedimentation of clastics due to the temporary erosion of metamorphic rocks and acid plutonites characterizes the Grenzland-Bänke (GB), deposited in a near-shore high-energy environment with intertidal to subtidal conditions (mega-ripples). The outer shelf sedimentation pattern of the Obere Pseudoschwagerinen-Kalke (OPK) is indicated by special associations of organisms in subtidal offshore areas.On this carbonate platform some knoll reefs of different age were built up during the Trogkofel stage (Carnic Alps, Sextener Dolomiten). Towards the east and southeast the platform shows again characteristics of the inner shelf (Klastische Trogkofel-Schichten).Synsedimentary tectonic activities during the late Lower Permian are manifested by the carbonate breccias of the Klastische Trogkofel-Schichten (Garnie Alps, Karawanken, Slovenia). The components of these breccias are dated as Middle Carboniferous to late Lower Permian. A further destruction of the platform at the Lower/Middle Permian boundary results in the sedimentation of the Tarviser Brekzie.The alpidic cycle Starts with the sedimentation of the clastic Grödener Schichten which during the first phase of sedimentation were deposited as continental clastics in South Tyrol but as predominately marine sediments in the Carnic Alps and in the Karawanken.The increasing transgression during the Upper Permian results in the deposition of bituminous sediments and basal evaporites of the Bellerophon-Schichten. In the south-western near-coast area the evaporites are dominating (facies fiammaza) whereas in northeastern South Tyrol gypsum with open marine carbonates prevails (facies badiotica). The Bellerophon-Schichten of the Carnic Alps indicate connections with the marine Zazar-Schichten in the Save area and with the limestones and dolomites of the Velebit mountains.

---

Résumé L'étude paléontologique et sédimentologique du Permien des Alpes carniques et des régions septentrionales, voisines du linéament périadriatique, a permis d'en tracér une equisse paléogéographique. - Les Untere Pseudoschwagerinen-Kalke (UPK) qui marquent le début des Rattendorfer Schichten, constituent une sédimentation cyclique de nature littorale, à laquelle succède, à la suite d'une activité érosive intense, les Grenzlandbänke (GB) caractérisés par un facies clastique de haute énergie, avec, dans ce dernier, des intervalles où apparaissent des roches métamorphiques et des roches plutoniques acides. Ce milieu, parcouru par des courants instables, nous indique un domaine mitoyen» subtidal-intertidal «(méga-ripples), à labase des marées. Des faunes et flores, variées et abondantes, sont distribuées dans une succession de zones écologiques de plus en plus distantes de la côte. Les Obere Pseudoschwagerinen-Kalke (OPK), déposés ensuite, se sont donc formés sur le plateau continental extérieur à caractère subtidal.Sur cette plate-forme à formations carbonatées, et au cours de l'étage de Trogkofel, des récifs ont pu s'installer, tandis que l'E et le SW de la plate-forme, plus rapprochés de la côte, ont reçu une sédimentation clastique (Klastische Trogkofelschichten). — Les mouvements de la fin du Permien inférieur se sont traduits par des brèches intercalées dans les Klastische Trogkofelschichten; des fragments de roches du Carbonifère moyen (étage de Moscow) sont inclus dans ces brèches. Enfin cette tendance arrive à son comble à la limite Permien inférieur/Permien moyen, lorsque la plateforme se désintègre avec formation de la Taviser Brekzie dans des effondrements local.Le cycle de sédimentation alpin débute par les Grödener Schichten — encore terrestres à l'Ouest, mais surtout marines dans les Alpes carniques et les Karawanken occidentales — et par les Bellerophonschichten marquant une mer en transgression.

---

, , (GB) , ( ) (UPK). , , , , . — , — , -, . . , . . , — — .

     

A preliminary study of D/H ratios of chlorites

Chemistry dependence of D of chlorites is inferred from data for natural chlorites. D of water equilibrated with those chlorites is estimated to be –2–8.     

Paleogeographic and paleotectonic response to magmatic processes: a case history from the Archean sequence in the Chibougamau area,Quebec

The Chibougamau area, Québec, is characteristic of the internal zone of the Archean Abitibi Orogenic Belt. The paleogeographic, paleotectonic and magmatic history of the Archean sequence in the Chibougamau area is subdivided into three stages.In the first stage a submarine volcanic chain formed mainly by the effusion of submarine lava flows composed of primitive, potash-poor, tholeiitic basalt. The volcanic chain gradually grew to sea level. In the second stage, volcanic islands emerged and grew. Mainly pyroclastic eruptions of strongly differentiated, calc-alkaline andesite and dacite concentrated on the volcanic islands, whereas effusion of basalt continued at first in the surrounding basin. A felsic volcaniclastic apron was deposited around the volcanic islands. In the third stage, the volcanic islands were uplifted and were eroded to the level of their subvolcanic plutons. The debris derived from this volcanic-plutonic terrain was deposited in downfaulted marine and continental basins. The contemporaneous volcanism was shoshonitic.The first paleogeographic stage is interpreted as the growth of an immature island arc. During the second stage, the island arc became mature and its crust was thickened by accretion of plutonic material. The third stage is a period of back-arc extension.

---

Zusammenfassung Das Gebiet von Chibougamau, Québec, ist characteristisch für die interne Zone des Archaischen Abitibi Orogens. Man kann seine paleogeographische, paleotectonische und magmatische Geschichte in drei Phasen gliedern.Eine submarine Vulkankette formte sich in der ersten Phase, hauptsächlich durch Effusion von submarinen Lavaergüssen aus primitivem, kaliarmen, tholeiitischem Basalt. Die Vulkankette wuchs langsam bis zum Meeresspiegel. Vulkanische Inseln bildeten sich und wuchsen während der zweiten paleogeographischen Phase. Vorwiegend pyroklastische Eruptionen von stark differenzierten, kalk-alkalischem Andesit und Dazit konzentrierten sich mehr und mehr auf den Inselvulkanen, während die Effusion von Basalt zunächst in den Becken noch stattfand. Ein Mantel aus felsitischen vulkanoklastischen Gesteinen wurde um die Inselvulkane abgelagert. Die dritte Phase begann mit einer Hebung der Inselvulkane und mit ihrer Erosion bis zum Niveau ihrer subvulkanischen Plutone. Der Detritus dieses vulkanisch-plutonischen Geländes wurde in marinen und kontinentalen Verwerfungsbecken abgelagert. Der gleichalte Vulkanismus ist shoshonitisch.Wir deuten die erste paleogeographische Phase als Wachstumsphase eines primitven Inselbogens. Während der zweiten Phase reifte der Inselbogen und seine Kruste verdickte sich durch Akkretion plutonischen Materials. Die dritte Phase ist eine Periode der Dehnung im Hinterland eines Inselbogens.

---

Résumé La région de Chibougamau, Québec, est caractéristique de la zone interne de la ceinture orogénique archéenne de l'Abitibi. Son évolution paléogéographique, paléotectonique et magmatique se subdivise en trois phases.Lors de la première phase paléogéographique, une chaîne sous-marine de volcans se formait, essentiellement par l'émission de coulées de lave composée de basalte primitif, hypopotassique, tholéiitique. Graduellement cette chaîne volcanique s'élevait jusqu'au niveau de la mer. A la phase suivante, des îles volcaniques émergeaient et croissaient. Des éruptions essentiellement pyroclastiques d'andésites et de dacites calco-alcalines et fortement différenciées se concentraient sur les îles tandis que l'effusion de laves basaltiques continuaient dans le bassin. Un manteau de roches volcaniclastiques felsiques se déposait autour des îles volcaniques. Lors de la troisième phase, les îles volcaniques furent soulevées et furent érodées jusqu'au niveau des masses plutoniques sub-volcaniques. Le débris de ce terrain volcano-plutonique fut déposé dans des bassins de faille marins et continentaux. Des shoshonites dominaient le volcanisme contemporain.Nous interprétons la première phase paléogéographique comme une phase de croissance d'un arc insulaire immature. Lors de la deuxième phase, 1'arc insulaire devenait mature et sa croûte s'epaissît par accrétion de matériel plutoni-que. Enfin, la troisième phase est une période d'extension en arrière d'un arc insulaire.

---

Chibougamau, Quebec, Abitibi. , . , . . , , . . , . - , , . . . . , , . , — . — . .

     

Jurassic kimberlites from Picton and Varty Lake,Ontario: Geochemical and stable isotopic characteristics

Micaceous ultramafic dikes of Jurassic age from Picton and Varty Lake, Ontario, consist mineralogically of olivine — phlogopite — serpentine — calcite-spinel. The rocks are characterized by abundant Ba-rich phlogopite (up to 6.5 wt.% BaO) and spinels with a diagnostic kimberlite trend-1. Compositionally the dikes are characterized by extreme silica-undersaturation (21–30 wt.% SiO₂), primitive Mg/(Mg + Fe^T) ratios (0.75–0.83), large enrichments of volatile components (CO₂ and H₂O), and relatively high abundances of both incompatible and compatible trace elements. The dikes exhibit pronounced enrichments of light rare earth elements (LREE) (La_N=320–1330) combined with strongly fractionated patterns (La_N/Yb_N=45–108). Calcite in the dikes is a primary magmatic phase, from textural relations and C-isotopic compositions ( ¹³C= –4.0 to –8.3). A calcite-rich aphanitic phase of the Picton dike is interpreted to be a late stage magmatic differentiate, which possibly involved olivine fractionation. Although the dikes lack most of the macrocrysts generally considered to be important diagnostic minerals of kimberlite magmatism, the geochemical, mineralogical and C- and O-isotopic characteristics collectively indicate that the dikes are evolved varieties of hypabyssal facies kimerlite.     

Orthogneisses of the Spessart crystalline complex,Northwest Bavaria: Indicators of the geotectonic environment?

The orthogneisses of the Spessart crystalline complex are derived from a granitic to granodioritic magma of S-type character which must have formed by anatexis of continental crust. It intruded into a relatively shallow crustal level, 410–420 Ma ago, at the Silurian. Trace element characteristics are consistent with a post-collision geotectonic environment testifying to extensional tectonics at the end of the Caledonian era.

---

Zusammenfassung Die Orthogneise des Spessartkristallins lassen sich von einem granitischen bis granodioritischen Magma von S-Typ-Charakter ableiten, das durch Anatexis kontinentaler Kruste entstanden sein mu\ und in ein relativ oberflächennahes Krustenniveau intrudierte. Die Platznahme erfolgte vor 410–420 Ma, d. h. im Silur. Die Spurenelement-Muster der Orthogneise entsprechen denen von Post-Kollisions-Granitoiden, was als Hinweis auf eine Phase der Dehnungstektonik am Ende der kaledonischen ära bewertet werden kann.

---

Résumé Les orthogneiss du Spessart sont dérivés d'un magma granitique à granodioritique de type S qui doit s'Être formé par anatexie de la croûte continentale. Ce magma a été intrudé dans un niveau peu profond de la croûte il y a 410–420 Ma c'est-à-dire au Silurien. La distribution des éléments en traces est en accord avec celle des granitoÏdes formés dans un contexte géodynamique de post-collision. Cette observation est en faveur d'une phase d'extension tectonique à la fin du cycle calédonien.

---

, — Wojcieszów-Kalke. , — . . , , , , .

     

Phase relationships and fluid inclusions characteristics of the metamorphosed,stratiform sulfide deposit Matchless,Namibia

Silicate assemblages in the wallrocks of the metamorphosed, stratiform sulfide deposit Matchless, Damara orogen, Namibia, yield temperatures between 550 and 625 °C and pressure of 6–8 kbar. Highest density fluid inclusions, containing either pure CO₂ or CO₂-CH₄/N₂ mixtures, display isochors which extrapolate through these metamorphic peak conditions. A second group of inclusions with the same fluid compositions exhibit isochors conforming to lower pressures, i.e. 3 kbar as deduced from sphalerite barometer, at the same temperatures. From these observations, we deduce an isothermal uplift path after peak of amphibolite facies metamorphism.

---

Zusammenfassung Silikatparagenesen im Nebengestein der metamorphen, schichtgebundenen Kupferlagerstätte Matchless, Damara-Orogen, Namibia, ergeben Temperaturen zwischen 550 und 625 °C und Drucke von 6–8 kbar beim Höhepunkt der Me-tamorphose. Fluideinschlüsse hoher Dichte, die mit CO₂ oder mit CO₂+CH₄/N₂ gefüllt sind, besitzen Isochoren, die durch diese P-T-Kombination verlaufen. Eine zweite Gruppe von Fluideinschlüssen mit der gleichen Zusammensetzung entspricht niedrigeren Druckbedingungen von etwa 3 kbar, wie sie sich aus dem Zinkblende-Barometer ableiten lassen, jedoch bei unveränderter Temperatur. Daraus läßt sich auf eine isotherme Heraushebung nach dem Höhepunkt der Metamorphose schließen.

---

Résumé Le dépôt de sulfure stratiforme métamorphique de Matchless (orogenèse Damara, Namibie) sont encaissés dans des roches dont les paragenèses silicatées indiquent des températures comprises entre 550° et 625° et des pressions de 6 à 8 Kb. Des inclusions fluides, très denses, contenant soit du CO₂ pur, soit des mélanges CO₂ + CH₄/N₂ fournissent des isochores qui traversent ce champ (P, T). Les isochores d'un deuxième groupe d'inclusions de mêmes compositions donnent, pour les mêmes températures, des pressions plus basses, de l'ordre de 3 Kb, déduites du baromètre à blende. On en déduit un soulèvement isothermique de la région après le pic du métamorphisme, qui s'est produit dans les conditions du faciès des amphibolites.

---

, Matchless, , , , , , 550 65 6 8 . , ₂, ₂ + CH₄/N₂ , . , 3 , , . , , .

     

Ammoniten-Ökologie am Beispiel des Oberjura

Zusammenfassung In vielen Fällen beeinflussen äußere Faktoren das Vorkommen der Ammoniten. Im Oberjura spielt die Wassertiefe eine große Rolle, daneben tritt die Wassertemperatur. Voraussetzungen der ökologischen Analyse sind bodenbezogenes Leben der Tiere und postmortale Autochthonie der Schalen. Methoden und Fehlerquellen werden besprochen. Aus der ökologischen Bindung vieler Ammoniten ergeben sich Folgen, vor allem für Stratigraphie, Phylogenie und Ontogenie.

---

In many cases external factors determine the occurence of the ammonites. In the Upper Jurassic the depth of the sea is of great importance, as well as the temperature of the water. Ecological analysis requires life of the animals close to the sea floor, and that the shells are autochthonous.Methods and sources of errors are discussed. The dependence on environment of many ammonites has consequences, especially for stratigraphy, phylogeny and ontogeny.

---

Résumé Souvent des facteurs extérieurs déterminent la présence des ammonites. Dans le Jurassique Supérieur la profondeur de la mer joue un grand rôle, aussi bien que la température de l'eau. L'analyse écologique doit supposer que les animaux vivent près du fond de la mer et que les coquilles sont autochtones. Les méthodes et les sources d'erreurs sont discutées. La dépendance des ammonites de leur milieu a des conséquences avant tout pour la stratigraphie, la phylogénie et l'ontogénie.

---

, . , . .