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1.
Dalradian metamorphic rocks, Lower Ordovician meta-igneous rocks (MGS) and Caledonian granites of the Connemara complex in SW Connemara all show intense retrograde alteration. Alteration primarily involves sericitization and saussuritization of plagioclase, the alteration of biotite and hornblende to chlorite and the formation of secondary epidote. The alteration is associated with sealed microcracks in all rocks and planes of secondary fluid inclusions in quartz where it occurs, and was the result of a phase of fluid influx into these rocks. In hand specimen K-feldspar becomes progressively reddened with increasing alteration. Mineralogical alteration in the MGS and Caledonian granites took place at temperatures 275±15°C and in the MGS Pfluid is estimated to be 1.5 kbar during alteration. The °D values of alteration phases are:-18 to-29 (fluid inclusions),-47 to-61 (chlorites) and-11 to-31 (epidotes). Chlorite 18O values are +0.2 to +4.3, while 18O values for quartz-K-feldspar pairs show both positively sloped (MGS) and highly unusual negatively sloped (Caledonian granites) arrays, diverging from the normal magmatic field on a - plot. The stable isotope data show that the fluid that caused retrogression continued to be present in most rocks until temperatures fell to 200–140°C. The retrograde fluid had D -20 to-30 in all lithologies, but the fluid 18O varied both spatially and temporally within the range-4 to +7. The fO2 of the fluid that deposited the epidotes in the MGS varied with its 18O value, with the most 18O-depleted fluid being the most oxidizing. The D values, together with low (<0) 18O values for the retrograde fluid in some lithologies indicate that this fluid was of meteoric origin. This meteoric fluid was probably responsible for the alteration in all lithologies during a single phase of fluid infiltration. The variation in retrograde fluid 18O values is attributed to the effects of variable oxygen isotope shifting of this meteoric fluid by fluid-rock interaction. Infiltration of meteoric fluid into this area was most likely accomplished by convection of pore fluids around the heat anomaly of the Galway granite soon after intrusion at 400 Ma. However convective circulation of meteoric water and mineralogical alteration could possible have occurred considerably later.  相似文献   

2.
Zusammenfassung Die geophysikalischen Untersuchungen am Störkörper von Bramsche, ca. 20 km N Osnabrück, deuten auf einen basischen Intrusivkörper in ca. 5 km Tiefe. Hohe Inkohlungsgrade in karbonischen bis kretazischen Sedimenten lassen eine starke Wärmequelle mit einem bis zu den Karbonhorsten südlich und westlich Osnabrück reichenden Kontakthof vermuten, mit einem Maximum der Inkohlung im Gebiet der geophysikalischen Anomalie.Während sich an den Karbonhorsten um Osnabrück sulfidisch-barytische Erze kretazischen Alters finden, fehlen jegliche Vererzungsspuren im Zentrum der Anomalie. Hier könnten lediglich Pyrophyllit und Quarzitisierungen im Malm des Gehns und das Vorkommen von Gümbelit im Piesberg-Karbon auf Auswirkungen der Intrusion hinweisen. Ausbildung (Faseraggregate der Phyllosilikate) und geologisches Auftreten (keine laterale Verteilung) sprechen aber für eine im weitesten Sinne lateral-sekretionäre Entstehung.Experimente vonNoll (1936) undAlthaus (1966) ergaben eine Bildungstemperatur für Pyrophyllit von ca. 390° C. Es finden sich jedoch keine pegmatitisch-pneumatolytischen oder katahydrothermalen Mobilisate in diesem Gebiet. Somit sollte die Bildungstemperatur für den Pyrophyllit niedriger gewesen sein. Selbst wenn die Bildungstemperatur bekannt wäre, wäre es schwierig, den hydrothermal gebildeten Pyrophyllit als geologisches Thermometer zu benutzen.- Geothermische Überlegungen zur Kalkulation der Intrusionstemperatur lassen sich hier somit nur noch mit Hilfe des Inkohlungsgrades vornehmen.
Geophysical researches at the Bramsche anomaly, about 20 km north of Osnabrück in NW-Germany indicate a basic intrusive body at the depth of about 5 km. A big source of heat with a contact zone reaching to the Carboniferous horsts south and west of Osnabrück is supposed by the increase of coalification in Carboniferous up to Cretaceous sediments, which has the highest degrees of coalification in the region of the geophysical anomaly.While there are sulfide deposits with barytic gangue of Cretaceous age at the Carboniferous horsts near Osnabrück, there are no ore-traces in the centre of the anomaly. Only the occurence of pyrophyllite and quartzites in the Malm of the Gehn-hills and the occurrence of gümbelite (Mg-hydromuscovite) in the Carboniferous sediments of Piesberg-horst may indicate the influence of the intrusion. - But habit (fibre-aggregates of the phyllosilicates) and geologic occurence (no lateral distribution) of these mineralisations suggest a formation by lateral secretion in a broader meaning of the term.Experiments byNoll (1936) andAlthaus (1966) proved a temperature of about 390° C for the formation of pyrophyllite. But there are no pegmatitic-pneumatolytic or kata-hydrothermal mobilisations in this district. Therefore it is assumed that the temperature of the formation may be lower under other conditions. Even if the temperature of this formation were known, it would be difficult to use pyrophyllite — formed under hydrothermal conditions — as a geologic thermometer. - Geothermal conclusions to calculate the temperature of the intrusion are only possible by using the decrease of volatile matter of the coals.
Résumé Les recherches géophysicales du corps failleux de Bramsche, à environ 20 km au nord d'Osnabrück font penser à un corps intrusit basique à 5 km sous la surface. De grands degrés d'houillification en des sédiments carbonifères et crétacés révèlent une forte source de chaleur avec une auréole de contact s'étendant jusqu'aux horsts carbonifères au sud et à l'ouest d'Osnabrück, avec un maximum d'houillification dans la région de l'anomalie géophysicale.Bien qu'on trouve des airains crétacés sulfurés avec barytine, aucune trace de minéralisation n'est visible au centre de l'anomalie. Ce n'est que la pyrophyllite et les quartzites dans le Malm du Gehn et l'existence de gümbelite (Mghydro-muscovite) dans le Piesberg-Karbon qui peuvent indiquer des effets d'intrusion. La structure et l'existence géologique font plutôt penser à une genèse latéralement sécrétionaire. Des conclusions géothermiques pour calculer la température d'intrusion ne sont à entreprendre qu'à l'aide du degré d'houillification.
(Bramsche) 20 (Osnabrück), , 5 . , - , * — . (Osnabrück) , . () (Gehn) - (Piesberg) . . , , . ()

Meinem verehrten Lehrer, Herrn Prof. Dr. H.Harder danke ich für die Anregung zu dieser Arbeit im Rahmen einer regionalen lagerstättenkundlichen Dissertation. Für weitere Hinweise und Diskussionen bin ich Herrn Prof. Dr. B.Brockamp verpflichtet.  相似文献   

3.
In closed magma systems SiO2 approximately measures differentiation progress and oxygen isotopes can seem to obey Rayleigh fractionation only as a consequence of the behaviour of SiO2. The main role of 18O is as a sensitive indicator of contamination, either at the start of differentiation ( 18Oinit) or as a proportion of fractionation in AFC. Plots of 18O vs SiO2-allow to determine initial 18O values for different sequences for source comparison. For NBS-28=9.60, the 18O at 48% SiO2-varies between a high 6.4 for Kiglapait (Kalamarides 1984), 5.9 for Transhimalaya, 5.8 for Hachijo-Jima (Matsuhisa 1979), 5.6 for Koloula (Chivas et al. 1982) and a low 5.3 for the Darran Complex, New Zealand. The Transhimalayan batholiths (Gangdese belt) were emplaced in the Ladakh-Lhasa terrane, between the present-day Banggong-Nujiang, and Indus-Yarlung Tsangbo suture zones, after its accretion to Eurasia. The gradient of the least contaminated continuous ( 18O vs SiO2-igneous trend line is similar to that of Koloula, and AFC calculations suggest a low secondary assimilation rate of less than 0.05 times the rate of crystallisation. Outliers enriched in 18O are frequent in the Lhasa, and apparently rare in the Ladakh transsect. Low- 18O (5.0–0) granitoids and andesites on the Lhasa-Yangbajain axis are the result of present day or recent near-surface geothermal activity; their quartzes still trace the granitoids to the Transhimalaya 18O trend line, but the distribution of low total rock or feldspar 18O values could be a guide to more recent heat flow and thermally marked tectonic lineaments. Two ignimbrites from Maqiang show hardly any 18O-contamination by crustal material.  相似文献   

4.
Zusammenfassung Kurze Übersicht über paläogeographische, paläotektonische und paläoklimatologische Probleme der Trias, unter Ausklammerung des Germanischen Beckens; allgemeiner Rahmen zu den Referaten der Trias-Tagung 1982 in Würzburg.
Short review of paleogeographic, paleotectonic and paleoclimatological problems of the Triassic system, outside of the Germanic Basin. General framework to the papers presented at the 1982 symposium on the Triassic.
Résumé Brève vue d'ensemble des problèmes paléogéographiques, paléotectoniques et paléoclimatiques du Trias, en dehors du bassin germanique. Cadre général des communications présentées lors du symposium sur le Trias de 1982.
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5.
34 igneous clasts of predominantly rhyolitic composition of the Parishholm- and Hareshaw-Conglomerate (Silurian, Hagshaw Hills inlier, Midland Valley, Scotland) have been analysed for major and trace element contents. The geochemical composition of the clasts indicates different source areas. Firstly, some clasts are derived from rhyolites of a within-plate setting (peralkaline rhyolites of oceanic islands or continental rifts) and secondly, other clasts are derived from calc-alkaline to high-K rhyolites. Such rhyolites erupt mainly above convergent plate boundaries, but occur also in continental areas of crustal extension. Both conglomerates were shed from the direction of the Southern Uplands into the Midland Valley. Since no calc-alkaline rhyolites are known in the Southern Uplands, a volcanic terrane should have been situated during the Silurian in the area where the Southern Uplands lie now. The geotectonic character of this terrane cannot unequivocally be identified with the help of the trace element data of the clasts. Therefore several models are discussed.
Zusammenfassung 34 Gerölle magmatischer Gesteine vorwiegend rhyolithischer Zusammensetzung aus dem Parishholm- und dem Hareshaw-Konglomerat (Silur, Hagshaw Hills inlier, Midland Valley, Schottland) wurden auf Haupt- und Spurenelementgehalte hin analysiert. Die geochemische Zusammensetzung der Gerölle deutet auf verschiedene Liefergebiete hin. Es handelt sich einmal um Gerölle von Rhyolithen aus einem Intraplatten-Gebiet (Peralkali-Rhyolithe ozeanischer Inseln oder kontinentaler Gräben) und zum zweiten um Gerölle von kalkalkalischen und kaliumreichen Rhyolithen. Solche Rhyolithe werden vorzugsweise über konvergierenden Plattengrenzen gefördert, sie treten aber auch in kontinentalen Dehnungsgebieten auf. Beide Konglomerate wurden aus der Richtung der Southern Uplands in das Midland Valley geschüttet. Da kalkalkalische Rhyolithe in den Southern Uplands unbekannt sind, dürfte im Silur ein vulkanisches Terraine in dem Gebiet, in welchem sich die Southern Uplands heute befinden, gelegen haben. Der geotektonische Charakter dieses vulkanischen Terraines lä\t sich mit Hilfe der Spurenelement-Daten der Gerölle nicht eindeutig festlegen. Es werden deshalb mehrere Modelle diskutiert.
Résumé Les auteurs ont analysé les éléments majeurs et en traces de 34 galets de roches magmatiques, en majorité rhyolitiques, prélevés dans les conglomérats de Parishholm et de Hareshaw (Silurien, Hagshaw Hills inlier, Midland Valley, Ecosse). Leur composition géochimique indique différentes provenances. D'une part, il s'agit de galets rhyolitiques d'une région intra-plaque (rhyolites peralcalines d'Îles océaniques ou de fossés continentaux), d'autre part, il s'agit de galets de rhyolites calco-alcalines et de rhyolites riches en potassium. Des rhyolites de ce type sont émises d'ordinaire au-dessus de sutures de plaques convergentes, mais elles se rencontrent aussi dans des régions continentales en extension. Les deux conglomérats proviennent du Sud, de la région des Southern Uplands. Comme des rhyolites calco-alcalines sont inconnues dans les Southern Uplands, on est amené à supposer l'existence, au Silurien, d'une accrétion («terrane») de nature volcanique dans la région occupée aujourd'hui par les Southern Uplands. Les teneurs des éléments en trace ne permettent pas de déterminer sans équivoque le caractère géotectonique de cette accrétion volcanique. Dans ces conditions, plusieurs modèles sont discutés.
34 Parishholm Hareshaw, , Hagshaw Hills inlier, Midland Valley, /, . . . , Intraplatten-Gebiet / , / - . . . , . . - , , , . . .
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6.
Hydrothermally-altered mesozonal synmetamorphic granitic rocks from Maine have whole-rock 18O (SMOW) values 10.7 to 13.8. Constituent quartz, feldspar, and muscovite have 18O in the range 12.4 to 15.2, 10.0 to 13.2, and 11.1 to 12.0, respectively. Mean values of Q–F ( 18Oquartz– 18Ofeldspar)=2.4 and Q–M ( 18Oquartz– 18Omuscovite)=3.3 are remarkably uniform (standard deviations of both are 0.2). Measured Q–F and Q–M values demonstrate that the isotopic compositions of the minerals are altered from primary magmatic 18O values but that the minerals closely approached oxygen isotope exchange equilibrium at subsolidus temperatures. Analyzed muscovites have D (SMOW) values in the range –65 to –82.Feldspars in the granitic rocks are mineralogically altered to either (a) muscovite+calcite, (b) muscovite+calcite+epidote, (c) muscovite+epidote, or (d) muscovite only. A consistent relation exists between the assemblage of secondary minerals and the oxygen isotope composition of whole rocks, quartz, and feldspar. Rocks with assemblage (a) have whole-rock 18O>12.1 and contain quartz and feldspar with 18O>13.8 and >11.4, respectively. Rocks with assemblages (b), (c), and (d) have whole-rock 18O<11.4 and contain quartz and feldspar with 18O< 13.1 and <11.0, respectively. The correlation suggests that the mineralogical alteration of the rocks was closely coupled to their isotopic alteration.Three mineral thermometers in altered granite suggest that the hydrothermal event occurred in the temperature range 400°–150° C, 100°–150° C below the peak metamorphic temperature inferred for country rocks immediately adjacent to the plutons. Calculations of mineral-fluid equilibria indicate that samples with assemblage (a) coexisted during the event with CO2-H2O fluids of and 18O=10.8 to 12.2 while samples with assemblages (b), (c), or (d) coexisted with fluids of and 18O=9.4 to 10.1. Compositional variations of the hydrothermal fluids were highly correlated: fluids enriched in CO2 were also enriched in 18O. Because CO2 was added to the granites during hydrothermal alteration and because fluids enriched in CO2 were enriched in 18O, some or all of the variation in 18O of altered granites may have been caused by addition of 18O to the rocks during the hydrothermal event. The source of both the CO2 and 18O could have been high-18O metasedimentary country rocks. The inferred change in isotopic composition of the granites is consistent with depletion of the metacarbonate rocks in 18O close to the plutons and with large volumes of fluid that were inferred from petrologic data to have infiltrated the metacarbonate rocks during metamorphism.A close approach of minerals to oxygen isotope exchange equilibrium in altered mesozonal rocks from Maine is in marked contrast to hydrothermally-altered epizonal granites whose mineral commonly show large departures from oxygen isotope exchange equilibrium. The difference in oxygen isotope systematics between altered epizonal granites and altered mesozonal granites closely parallels a differences between their mineralogical systematics. Both differences demonstrate the important control that depth exerts on the products of hydrothermal alteration. Deeper hydrothermal events occur at higher temperature and are longer-lived. Minerals and fluid have sufficient time to closely approach both isotope exchange and heterogeneous chemical equilibrium. Shallower hydrothermal events occur at lower temperatures and are shorter-lived. Generally there is insufficient time for fluid to closely approach equilibrium with all minerals.  相似文献   

7.
The Strange Lake plutonic complex consists of three annular Mid-Proterozoic arfvedsonite-aegirine-bearing alkali granites emplaced in the Rae province of the Canadian Shield. The mineralogy, chemistry and structural setting of the complex are very similar to that of many peralkaline central salic complexes associated with the development of the Gardar rift in southern Greeland. The Strange Lake granites are highly fractionated (Rb/Sr=5 to 160 and K/Rb=27 to 120) and carry unusually high abundances of HFSE and REE-bearing exotic minerals (e.g. pyrochlore, gittinsite, elpidite, gadolinite and kainosite) which are reflected in the elevated HFSE (e.g.Zr=307 to 16800 ppm) and REE (e.g. La=84 to 1337 ppm) contents of the granites. HFSE and REE increase from the oldest intrusive unit, which is hypersolvus and unaltered, to the youngest, which is subsolvus and metasomatized. The unaltered granites display a restricted range of 18O values (+8.2 to+9.6) and low 18O signatures for fresh arfvedsonite/aegirine (+4.8 to+5.2). Anomalously high CaO (0.7 to 3.2 wt%) and MgO (0.1 to 0.6wt%) concentrations characterize the altered subsolvus granites. These rocks also have elevated whole rock 18O values (+9.6 to +11.9), negative 18Oquartz-alk.feld. (-0.1 to-1.6), and high 18O values of altered arfvedsonite (i.e.+6.5 to 13.75) that correlates positively with whole rock 18O values. The chemical and isotopic data are consistent with a model in which the least evolved alkali granites are formed through differentiation from trachytic (syenitic) parents. Extreme HFSE and REE-enrichment may have been accomplished by differentiation through fractional crystallization and heterogenous distribution of F-rich silicic residual melts in which the REE and HFSE are transported as fluorocomplexes. The O-isotopic values are consistent with the circulation of low temperature (lt;200°C) hydrothermal fluids in the youngest subsolvus intrusive unit which caused extensive Ca (Mg and Sr) metasomatism and fluorine leaching, widespread hematization, and remobilization of the HFSE and REE.  相似文献   

8.
The world-class Idrija mercury deposit (western Slovenia) is hosted by highly deformed Permocarboniferous to Middle Triassic sedimentary rocks within a complex tectonic structure at the transition between the External Dinarides and the Southern Alps. Concordant and discordant mineralization formed concomitant with Middle Triassic bimodal volcanism in an aborted rift. A multiple isotopic (C, O, S) investigation of host rocks and ore minerals was performed to put constraints on the source and composition of the fluid, and the hydrothermal alteration. The distributions of the 13C and 18O values of host and gangue carbonates are indicative of a fracture-controlled hydrothermal system, with locally high fluid-rock ratios. Quantitative modeling of the 13C and 18O covariation for host carbonates during temperature dependent fluid-rock interaction, and concomitant precipitation of void-filling dolomites points to a slightly acidic hydrothermal fluid (13C–4 and 18O+10), which most likely evolved during isotopic exchange with carbonates under low fluid/rock ratios. The 34S values of hydrothermal and sedimentary sulfur minerals were used to re-evaluate the previously proposed magmatic and evaporitic sulfur sources for the mineralization, and to assess the importance of other possible sulfur sources such as the contemporaneous seawater sulfate, sedimentary pyrite, and organic sulfur compounds. The 34S values of the sulfides show a large variation at deposit down to hand-specimen scale. They range for cinnabar and pyrite from –19.1 to +22.8, and from –22.4 to +59.6, respectively, suggesting mixing of sulfur from different sources. The peak of 34S values of cinnabar and pyrite close to 0 is compatible with ore sulfur derived dominantly from a magmatic fluid and/or from hydrothermal leaching of basement rocks. The similar stratigraphic trends of the 34S values of both cinnabar and pyrite suggest a minor contribution of sedimentary sulfur (pyrite and organic sulfur) to the ore formation. Some of the positive 34S values are probably derived from thermochemical reduction of evaporitic and contemporaneous seawater sulfates.Editorial handling: P. Lattanzi  相似文献   

9.
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.  相似文献   

10.
This paper deals with barite from stratiform, karst, and vein deposits hosted within Lower Paleozoic rocks of the Iglesiente-Sulcis mining district in southwestern Sardinia. For comparison sulfates from mine waters are studied. Stratiform barite displays 34S=28.8–32.1, 18O=12.7–15.6, and 87Sr/86Sr=0.7087, in keeping with an essentially Cambrian marine origin of both sulfate and strontium. Epigenetic barite from post-Hercynian karst and vein deposits is indistinguishable for both sulfur and oxygen isotopes with 34S=15.3–26.4 and 18O=6.6–12.5; 87Sr/86Sr ratios vary 0.7094–0.7140. These results and the microthermometric and salinity data from fluid inclusions concur in suggesting that barite formed at the site of mineralization by oxidation of reduced sulfur from Cambrian-Ordovician sulfide ores in warm, sometimes hot solutions consisting of dilute water and saline brine with different 18O values. The relative proportion of the two types of water may have largely varied within a given deposit during the mineralization. In the karst barite Sr was essentially provided by carbonate host rocks, whereas both carbonate and Lower Paleozoic shale host rocks should have been important sources for Sr of the vein barite. Finally, 34S data of dissolved sulfate provide further support for the mixed seawater-meteoric water composition of mine waters from the Iglesiente area.  相似文献   

11.
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.  相似文献   

12.
Carbon and oxygen isotopic covariations in hydrothermal calcites   总被引：5，自引：0，他引：5  
Isotopic covariations of carbon and oxygen in hydrothermal calcites are quantitatively modeled in terms of the following three mixing processes: (1) mixing between two different fluids which leads to the precipitation of calcite; (2) mixing between fluid and rock: (a) calcite precipitation due to fluid/rock interaction, (b) secondary alteration of primary calcite by interaction with a subsequent fluid. The models are derived from mass balance equations. A distinction among the three mixing processes can be made on a 13C vs 18O diagram, which places important constraints on the genesis of hydrothermal mineralization. The variables which control the ultimate isotopic composition of hydrothermal calcites include the composition of the initial fluid and the wallrock, temperature, and dissolved carbon species. Owing to significant temperature-dependent fractionation effects during equilibrium precipitation of calcite from a hydrothermal fluid, the mixing processes may be distinguished by telltale patterns of isotopic data in 13C vs 18O space. In particular, caution must be exercised in postulating the fluid mixing as the cause for mineral deposition. This is demonstrated for hydrothermal Pb-Zn deposits in the western Harz Mountains, Germany. A positive correlation between 13C and 18O values is observed for calcites from the Bad Grund deposit in the Upper Harz. Two sample profiles through calcite veins show similar correlations with the lowest -values at the center of the veins and the highest -values at the vein margins. Because the correlation array has a greater slope than for calcite precipitation at equilibrium in a closed system and because fluid mixing may not proceed perpendicular to the vein strike, it is assumed that a fluid/rock interaction is responsible for the observed correlation and thus for the precipitation of calcite. A deep-seated fluid is inferred with a 13C value of — 7% and a 18O value of +10%., as well as H2CO3 as the dominant dissolved carbon species; precipitation temperatures of the calcites are estimated to be about 280 170°C. Quite different isotopic distributions are observed for calcites from the St. Andreasberg deposit in the Middle Harz. An alteration model is suggested based mainly on the isotopic distribution through a calcite vein. In addition to a primary fluid which has the same isotopic composition as that in the Bad Grund deposit and thus seems to be responsible for the precipitation of calcite associated with sulfides, an evolved, HCO 3 - -dominant subsurface fluid with 13C about -20 — 15% and 18O 0% is deduced to alter the primary calcite at low temperatures of 70 40°C.  相似文献   

13.
Isotopic compositions of carbon and oxygen are studied in different (rhodochrosite, calcareous-rhodochrosite, and chlorite–rhodochrosite) types of manganese carbonate ores from the Usa deposit (Kuznetskii Alatau). The 13C value varies from –18.4 to –0.7, while the 18O value ranges between 18.4 and 23.0. Host rocks are characterized by higher values of 13C (–1.9 to 1.0) and 18O (21.2 to 24.3). The obtained isotope data suggest an active participation of oxidized organic carbon in the formation of manganese carbonates. Manganese carbonate ores of the deposit are probably related to metasomatic processes.  相似文献   

14.
REE (rare-earth-element) and Th mineralization at the Rodeo de Los Molles deposit occurs within an elliptical body of hydrothermally altered rocks (fenite) located in a biotite monzogranite of the Las Chacras batholith. Ore assemblages are found as isolated patches of intergrown britholite, allanite, apatite, bastnaesite, fluorite, sphene, quartz, and aegirine-augite, as well as nodules of uranothorite and late-stage veins of calcite, fluorite, and bastnaesite. Composition-volume computations suggest that the fenite was produced by alteration of the biotite monzogranite by addition of K and Na, and loss of Ca and Sr. Petrographic evaluations indicate that microcline and plagioclase have been replaced by perthite, and biotite was converted to aggregates of clinochlore, anatase, kaolinite, and hematite. Relict biotite is characterized by lower Fe/(Fe+Mg) and Ti values with progressive alteration. Fluorine-rich phlogopite is present in mineralized areas, but textural evidence suggests that it was not produced via biotite alteration. Mass-balance constraints also show that Ca and Mg in ore zones may result from redistribution, rather than their being a result of external derivation. The 18O values of quartz (8.6–11.1) and feldspar (7.8–10.6) suggest that feldspar continued to exchange oxygen isotopes with a fluid to lower temperatures than did quartz. Feldspars equilibrated with a fluid of 18O8 at a fluid/rock ratio less than 1. The 18O values of quartz and aegirine-augite that crystallized during REE mineralization also suggest equilibration with a fluid of 18O8. The D values of biotite (-83 to-120) are relatively low for igneous rocks and are thought to have resulted from exsolution of a D-enriched magmatic vapor. The D values of both mineralized and barren fenites are consistent with equilibration with fluid of magmatic origin. Meteoric water was involved in the production of calcite and clinochlore alteration, and late-stage calcite-fluorite-bastnaesite veins. The 13C values of calcite and bastnaesite (-7.8 to-13.5%) suggest that carbon was derived by leaching of carbon from igneous and/or enclosing metamorphic rock types, and that a majority of carbon ultimately was derived from sedimentary organic meterial.  相似文献   

15.
Preliminary studies have been made on the distributions of oxygen and sulphur isotopes in the Rosebery, Mount Farrell, and Mount Lyell ores. These ores lie in Cambrian geosynclinal volcanic rocks in West Tasmania. At each locality the sulphur of the sulphide minerals has a distinctive degree of enrichment in 34S in relation to sulphur in meteorites and a narrow range of 34S values. The dominant ore at Mount Lyell (mainly pyrite-chalcopyrite) has an average 34S value of +7.0, the main lode at Rosebery (pyrite-sphalerite-galenachalcopyrite) averages +10.9, and the Mount Farrell ore (galena-sphalerite) averages +14.1. The degree of enrichment does not appear to be related to local, near-surface geological factors. Other ores of geosynclinal volcanic type with similar mineralogy also show narrow ranges in 34S and varying enrichments in 34S. Barite from a concordant sulphide-barite-carbonate lode at Rosebery has an average 34S of +38.1 and an average 18O of +10.7. Barite from veins at Mount Lyell has an average 34S of +25.3 and an average 18O of +10.6.
Die Verteilung von Sauerstoff- und Schwefel-Isotopen in den Erzkörpern von Rosebery, Mount Farrell und Mount Lyell wurde untersucht. Die Erzkörper sind in kambrische, geosynklinale vulkanische Gesteine Westtasmaniens eingebettet. An jeder dieser Lagerstätten zeigt der Schwefel der Sulfiderze einen charakteristischen Anreicherungsgrad an 34S im Verhältnis zum Meteoritenschwefel und einen eng begrenzten Bereich der 34S-Werte. Die Erze des Mount Lyell-Lagers (hauptsächlich Pyrit-Chalkopyrit) zeigen überwiegend einen 34S-Durchschnittswert von +7.0, das Hauptlager von Rosebery (Pyrit-Sphalerit-Galenit-Chalkopyrit) +10.9, und des Mount Farrell-Erz (Galenit-Sphalerit) +14.1. Der Anreicherungsgrad scheint nicht mit den lokalen geologischen Faktoren verbunden zu sein. Auch andere Erzkörper geosynklinaler vulkanischer Art von ähnlicher mineralogischer Struktur zeigen eng begrenzte 34S-Werte und 34S-Anreicherungsvariationen. Der Baryt des konkordant aufgebauten Sulfid-Baryt-Carbonat-Lagers bei Rosebery hat einen 34S-Durchschnitt von +38.1 und einen 18O-Durchschnitt von +10.7. Der Baryt aus den Erzgängen von Mount Lyell ist durch einen 34S-Durchschnitt von +25.3 und einen 18O-Durchschnitt von +10.6 charakterisiert.
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16.
For the first time 18O and 13C values from carbonates and D values of individual n-alkanes were used to reconstruct palaeohydrological conditions in a lagoon at the southern margin of the Central European Zechstein Basin (CEZB). A 12-m core covering the complete Ca2 interval and adjacent anhydrites (A1 and A2) was analyzed for 18O and 13C values of dolomitized carbonates and D values of individual n-alkanes. 18Ocarb values (+2 to +5 vs. VPDB) were strongly influenced by evaporation and temporal freshwater input into the lagoon. The 13Ccarb values (–1 to +4 vs. VPDB) were controlled mainly by changes in primary production. Both isotopic ratios show an inverse relationship throughout most of the core, contradicting diagenetic alteration, since 13Ccarb values are not altered significantly during dolomitization. Assuming a temperature range of 35–40 °C in the lagoon, 18Ocarb values of +2.5 to +8 (vs. VSMOW) for the lagoonal water can be reconstructed. The lagoon may have desiccated twice during the Ca2 interval, as indicated by very high 18Ocarb and low 13Ccarb values, coinciding with increasing amount of anhydrite in the analyzed sample. These events seem to reflect not just local but a regional intra-Ca2 cyclicity. Measured D values of the short-chain n-alkanes, namely n-C16 and n-C18 which are widely used as indicators for photosynthetic bacterial and algal input, reflect the isotopic composition of the lagoonal water. Assuming constant fractionation during incorporation of hydrogen into lipids of –160, an average D value of +70 (vs. VSMOW) can be reconstructed for the lagoonal water, accounting for very arid conditions. The long-chain n-alkanes n-C27, n-C28, n-C29 and n-C30, thought to be derived from the leaf waxes of terrestrial higher plants, were shown to be depleted in D relative to the short-chain alkanes, therefore indicating a different hydrogen source. Terrestrial plants in arid areas mainly use water supplied by precipitation. By using a smaller fractionation of –120 due to evaporation processes in the leaves, reconstructed values vary between –74 and –9 (vs. VSMOW). These values are not indicating extremely arid conditions, implying that the long-chain n-alkanes were transported trough wind and/or rivers into the lagoon at the Zechstein Sea coast. Dwater values, reconstructed using the n-C16 alkane and 18O water values, independently reconstructed on the same sample using the temperature dependant fractionation for dolomites are good agreement and suggest high amounts of evaporation affecting the coastal lagoon. Altogether, our results indicate that hydrogen isotopic ratios of n-alkanes give information on their origin and are a useful proxy for palaeoclimatic reconstruction.  相似文献   

17.
Carbon and oxygen isotope analyses were made of representative samples of calcite and quartz from the carbonate deposits in the Tolfa Mountains mining district. Measurements were also made of hydrogen isotope compositions, filling temperatures and salinities of fluid inclusions in these minerals. There are three stages of mineralization at Tolfa. In stage I, characterized by calc-silicate hornfels, the carbonates have relatively high 18O values of 14.5 to 21.6 suggesting a rather low water/rock ratio. 13C values of –0.3 to 2.1 indicate that appreciable decarbonation or introduction of deep-seated carbon did not occur. Stage II is marked by phanerocrystalline carbonates; 18O values of 13.1 to 20.0 and 13C values of 0.7 to 5.0 identify them as hydrothermal veins rather than marbles. D values of –56 to –50 for inclusion fluids suggest a possible magmatic component to the hydrothermal fluid. Filling temperatures of coarse-grained samples of Calcite II are 309° to 362° C with a salinity range of 5.3 to 7.1 weight percent NaCl. Calculated 18O values of 11–12 for these fluids are again indicative of low water/rock ratios. The sparry calcites of stage III have 18O and 13C values of 8.1 to 12.9 and –1.7 to 3.2, respectively. D values of inclusion fluids are –40 to –33, clearly heavier than in earlier stages and similar to values of modern local ground waters. A salinity measurement of <0.1 weight percent NaCl in a sample of Calcite III is compatible with a relatively unaltered ground water origin for this fluid. Precipitation of the sparry calcite took place at much lower temperatures, around 160° C. For quartz, 18O values of 9.3 to 12.4 and D values for inclusions of –53 to –28 are consistent with its late occurrence and paragenetic link with associated carbonates.  相似文献   

18.
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  相似文献   

19.
A systematic study of the auriferous quartz veins of the Val-dOr vein field, Abitibi, Quebec, Canada, demonstrates that the C, O, S isotope composition of silicate, carbonate, borate, oxide, tungstate and sulphide minerals have a range in composition comparable to that previously determined for the whole Superior Province. The oxygen isotope composition of quartz from early quartz–carbonate auriferous veins ranges from 9.4 to 14.4 whereas later quartz-tourmaline-carbonate veins have 18Oquartz values ranging from 9.2 to 13.8 . Quartz-carbonate veins have carbonate (18O: 6.9–12.5 ; 13C: –6.2– –1.9 ) and pyrite (34S: 1.2 and 1.9 ) isotope compositions comparable to those of quartz-tourmaline-carbonate veins (18O: 7.9–11.7 ; 13C: –8.0 – –2.4 ; 34S: 0.6–6.0 ). 18Oquartz values in quartz-tourmaline-carbonate veins have a variance comparable to analytical uncertainty at the scale of one locality, irrespective of the type of structure, the texture of the quartz or its position along strike, across strike or down-dip a vein. In contrast, the oxygen isotope composition of quartz in quartz-tourmaline-carbonate veins displays a regional distribution with higher 18O values in the south-central part of the vein field near the Cadillac Tectonic Zone, and which 18O values decrease regularly towards the north. Another zone of high 18O values in the northeast corner of the region and along the trace of the Senneville Fault is separated by a valley of lower 18O values from the higher values near the Cadillac Tectonic Zone. Oxygen isotope isopleths cut across lithological contacts and tectonic structures. This regional pattern in quartz-tourmaline-carbonate veins is interpreted to be a product of reaction with country rocks and mixing between (1) a deep-seated hydrothermal fluid of metamorphic origin with minimum 18O=8.5 , 13C=0.6 and 34S=–0.4 , and (2) a supracrustal fluid, most likely Archean seawater with a long history of water-rock exchange and with maximum 18O=3.9 , 13 C=–5.6 and 34S=5.0 .  相似文献   

20.
Boron isotope variations in nature: a synthesis   总被引：9，自引：0，他引：9  
The large relative mass difference between the two stable isotopes of boron, 10B and 11B, and the high geochemical reactivity of boron lead to significant isotope fractionation by natural processes. Published 11B values (relative to the NBS SRM-951 standard) span a wide range of 90. The lowest 11B values around — 30 are reported for non-marine evaporite minerals and certain tourmalines. The most 11B-enriched reservoir known to date are brines from Australian salt lakes and the Dead Sea of Israel with 11B values up to +59. Dissolved boron in present-day seawater has a constant world-wide 11B value of + 39.5. In this paper, available 11B data of a variety of natural fluid and solid samples from different geological environments are compiled and some of the most relevant aspects, including possible tracer applications of boron-isotope geochemistry, are summarized.
Résumé La grande différence relative de masse entre les isotopes stables du bore, 10B et 11B, et la grande réactivité geochimique du bore ont pour conséquence un fractionnement isotopique naturel important. Les valeurs de 11B publiées (par rapport au standard NBS SRM-951) varient de 90. Les valeurs de 11B les plus basses (–30) correspondent aux evaporites non-marines et à certaines tourmalines. Le réservoir le plus enrichi en 11B est représenté par les saumures des lacs salés d' Australie et par la Mer Morte en Israël, qui ont des valuers de 11B allent jusqu'à + 59. L'eau de mer a une valeur de 11B mondialement constante de + 39.5. Des valeurs de 11B des solutions naturelles ainsi que des roches et minéraux de différentes origines, publiées jusqu'à présent, sont présentées ici. En outre quelques aspects importants concernant la géochimie des isotopes du bore y compris quelques applications sont exposés.
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