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1.
Prof. Dr. Adolf Seilacher 《International Journal of Earth Sciences》1967,56(1):189-200
Zusammenfassung Tektonischer, sedimentologischer und biologischer Aspekt liefern eine gleichwertige Teildefinition für die echte Flysch-Fazies. Sind davon eine bzw. zwei nicht erfüllt, so kann nur von einem in bestimmter Richtung atypischen Flysch bzw. flysch-ähnlichen Gestein die Rede sein. Eine solche Unterscheidung ist auch genetisch bedeutsam.
Frequent association of certain tectonical, sedimentological, and biological features at various points of earth history demonstrates the significance of the flysch concept. Examples intermediate to other facies types are relatively rare and differ from true flysch in either one, or two, of the three aspects. Tectonically, sedimentologically or biologically aberrant flysch, and formations that are flysch-like with regard to one aspect may be distinguished accordingly.
Résumé Une définition valable du Flysch-faciès peut être trouvée sous l'aspect tectonique, sédimentologique ou biologique. S'il en manque un ou deux, il y a seulement un Flysch atypique ou bien une roche pareille au Flysch. Une telle distinction est importante au point de vue génétique.
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2.
Summary Metamorphosed carbonatites and related skarn deposits, located in Fuerteventura Basal Complex, contain unusual Sr-rich minerals. Maximum SrO concentration in the following minerals are: calcite, 7.23wt%; apatite, 5.22wt%; epidote, 11.64wt%; clinozoisite, 1.25wt%; allanite, 5.63wt%; britholite, 4.11wt% and a Sr–Na aluminosilicate (probably stronalsite), 16.44wt% SrO. Calcite and apatite are chemically similar to those found in carbonatites and are therefore considered to be of igneous origin. Textural evidence indicates that the first skarn stage garnet+diopside+Sr–Na aluminosilicate formed as the result of chemical interaction between carbonatites and adjacent silicate rocks. The formation of Sr-bearing epidote/clinozoisite, allanite and britholite appears to be related to the release of Sr into the fluid phase from the breakdown of high temperature assemblages during the retrograde skarn stage. During the final evolution stages, further alteration of britholite by bastnäsite and törnebohmite took place. The occurrence of REE minerals shows that the fluids responsible for this metasomatism must also have transported significant quantities of REE. 相似文献
3.
William J. Green Brian R. Stage Bonnie Jo Bratina Shannon Wagers Adam Preston Kevin O’bryan Joseph Shacat Silvia Newell 《Aquatic Geochemistry》2004,10(3-4):303-323
Lake Vanda is a closed-basin, permanently ice-covered lake located in the Wright Valley of Antarctica. The lakes more important geochemical features include the fact that it is fed by a single glacial melt water stream for only 6–8weeks out of the year; that it has remained stratified for more than a millennium; and that, like other lakes in the region, it is remote from anthropogenic influence. These, together with the fact that it is among the least biologically productive lakes in the world, make it an ideal system for examining the transport, cycling and fate of trace metals in the aquatic environment. Like others before us, we view this lake as a natural geochemical laboratory, a flask in the desert. This paper presents the first set of closely spaced, vertical, profiles for dissolved and particulate Mn, Fe, Ni, Cu, Zn and Cd in the water column. Despite the absence of an outflow, metals in the fresh upper waters of the lake have extremely low concentrations, in the pico-molar to nano-molar range, and are partitioned largely into dissolved rather than particulate phases. Efficient metal scavenging by particles from these oxygen-rich waters is indicated. Significant increases in metal concentrations begin to appear at depth, between 57 and 60m, and these increases coincide with the onset of manganese oxide dissolution in oxic, but lower pH waters. Vertical profiles suggest that the entire suite of trace metals (Ni, Cu, Zn, and Cd) is being released from manganese oxide carrier phases. Thermodynamic analysis indicates that Mn3 O4 (i.e., the mineral hausmannite) may be important in metal sequestration and recycling in the deeper waters of Lake Vanda. Manganese-reducing organisms reported by Bratina etal. (1998) are active in the zone of metal release and these could also contribute to the observed cycling. 相似文献
4.
Summary On Diego de Almagro Island in Chilean Patagonia (51°30S), a convergent strike slip zone, the Seno Arcabuz shear zone, separates the Diego de Almagro Metamorphic Complex from very low grade metagreywackes in the east, which were intruded by Jurassic granitoids. The Diego de Almagro Metamorphic Complex is composed of a metapsammopelitic sequence containing blueschist intercalations in the west and (garnet) amphibolite lenses in the east. Peak metamorphic conditions (stage I) at 9.5–13.5kbar, 380–450°C in the blueschist and at 11.2–13.2, 460–565°C in the amphibolite indicate subduction and accretion at different positions within the deepest part of the accretionary wedge. A K–Ar age of 117±28Ma of amphibole approximately dates the peak of metamorphism in the amphibolite. The early retrograde stage of metamorphism occurred under static conditions and resulted in localized equilibration (stage II) at 6.3–9.6kbar, 320–385°C in the blueschist and 6.1–8.4kbar, 310–504°C in the amphibolite. Both P-T paths converge within a midcrustal level.In contrast, an orthogneiss of trondhjemitic composition occurring within the Seno Arcabuz shear zone is associated with a garnet mica-schist containing a high temperature/intermediate pressure assemblage formed at 4.9–6.5kbar, 580–690°C. A muscovite K–Ar age of 122.2±4.6Ma dates cooling after this event which is related to a concomitant magmatic arc. These rocks were overprinted by a mylonitic deformation, which is caused by convergent strike slip shearing and ends during formation of a retrograde phengite-chlorite-stilpnomelane assemblage at a minimum pressure of approximately 5.7kbar (at 300°C).Zircon fission track ages from rocks of the Seno Arcabuz shear zone are 64.9±2.7 and 64.9±2.7Ma; they record the end of shearing in the Seno Arcabuz shear zone that juxtaposed all rocks in the middle crust. Zircon fission track ages ranging from 78 to 105Ma in the South Patagonian batholith to the east indicate earlier cooling through 280°C. The rocks of the Diego de Almagro Metamorphic Complex were initially slowly exhumed and resided at a midcrustal level before being emplaced via shearing in the Seno Arcabuz shear zone. Apatite fission track ages (54±8Ma) from the Seno Arcabuz shear zone show that exhumation and cooling rates increased after this event. The incorporation of continental crust within the subduction system was a late process, which modified the Cretaceous accretionary wedge, resulting in considerable shortening of the convergent margin. 相似文献
5.
K. J. Langthaler J. G. Raith D. H. Cornell H. J. Stein F. Melcher 《Mineralogy and Petrology》2004,82(1-2):33-64
Summary Vein-type Mo mineralization at Alpeiner Scharte occurs in the Penninic units of the western Tauern Window in the Eastern Alps. Three types of previously undated metagranitoids (central gneisses) are distinguished and preserve intrusive contacts with pre-Alpine metamorphosed supracrustal rocks. The granitic protoliths represent fractionated late to post-orogenic, calc-alkaline, I-type magmas with minor S-type components. The Mo veins are restricted to a biotite and alkali feldspar-rich gneiss variety and occur in E–W trending normally sub-vertical quartz veins with adjacent thin discontinuous garnet- and biotite-rich zones; the latter are interpreted as metamorphosed vein selvages. Prior to this work the age of the intrusive host rocks as well as the age of Mo mineralization were unknown.The pre-Alpine Mo deposit and its host rocks were affected by four Alpine deformation events (D1–D4) and Young-Alpine regional metamorphism. The P-T conditions of this metamorphic event were 550°C and 8kbar and are in agreement with results of previous regional studies.Zircon grains from two orthogneiss samples were dated with the U–Pb method using ion probe techniques. Zircons from the metagranitic host rock of the Mo-veins yielded an emplacement age of 306.8±3.8Ma (2). A second sample from a more leucocratic gneiss lacking Mo-veins gave 305.0±6.6Ma (2). Re–Os dating of molybdenite from the veins yielded an age of 306.8±3.1Ma, in good agreement with the U–Pb zircon ages.This study confirms one of two alternative hypotheses discussed in the literature. It supports the idea that vein-type Mo-mineralization in the western Tauern Window is genetically related to Late Carboniferous (Westphalian) granitoids that were emplaced during the late to post-orogenic stage of the Variscan orogeny. They do not constitute an Alpine metamorphic-hydrothermal deposit. This study further confirms the strength of the Re–Os molybdenite chronometer, in that it was unaffected by subsequent Alpine medium grade regional metamorphism.Present address: Kremstalstraße 32, A-4501 Neuhofen an der Krems, Austria 相似文献
6.
Summary The investigated Al-phosphate- and Al-borosilicate-bearing metaquartzite horizon belongs to the Middle Proterozoic Serra de Vereda member of the São Marcos Formation of the northern Espinhaço fold belt. Outcrops are located in the NNW–SSE trending hills of the Serra de Canas/Cana Brava (Northern Serra do Espinhaço, State of Bahia, NE Brazil) about 10km west of the town of Boquira. Sky blue lazulite and deep blue to lilac dumortierite are enriched in layers which sometimes show relic cross bedding. The occurrence of hematite patches and layers is typical. In rocks of type A, phosphorus contents range from 1.89wt.% to 10.73wt.% P2O5 and boron contents are mostly below 10ppm whereas in the rocks of type B phosphorus contents are below 1% and boron contents reach 2600ppm with a mean value of 1139ppm. REE distribution patterns of rocks are predominantly controlled by the amount of xenotime, monazite and zircon. Oxygen thermometry on quartz and hematite and the stability of kyanite, augelite, trolleite and berlinite allow to estimate the minimum metamorphic peak P-T conditions at 475°C and 3.8kbar i.e. within the stability field of scorzalite–lazulite and dumortierite. The association of Al-phosphates with hematite layers provides evidence for the deposition of the metaquartzite protolith in a seawater-fed sabkha-like sand flat fringing the Espinhaço rift. It is proposed that apatite, Al-phosphates and Al-borosilicates were chemically precipitated together with iron hydroxides from pore fluids. The antithetic behaviour of phosphorus and boron contents in the metaquartzites is the consequence of an influx of toxic boron-rich water that drastically affected algae populations and consequently reduced phosphorus precipitation. 相似文献
7.
A study of Barrovian metamorphic zones in a belt of essentially pelitic schists in Singhbhum, E. India, broadly completes the metamorphic map of the main Singhbhum anticlinorium. Isograds run parallel with the sub-horizontal fold-axes and close where the latter shows considerable plunge. The index mineral of the highest zone crystallised succeeding crystallisation of lower grade ones in their true order in that zone. A particular index mineral presumably crystallised in successive lower zones progressively in time. Intensity of metamorphism and deformation was broadly simultaneous.
Zusammenfassung Eine Untersuchung der barrowischen metamorphen Zonen in einem Gebiet von im wesentlichen pelitischen Schiefern in Singhbhum (östliches Indien) vervollständigt die Karte vom Metamorphikum des Singhbhum-Hauptantiklinoriums. Die Isograden erstrecken sich parallel zu den subhorizontalen Faltenachsen und schließen sich, wo die Faltenachsen beträchtlich untertauchen. Leitmineralien der höchsten Zone kristallisierten zeitlich nach denen der niedrigeren Zonen. Ein bestimmtes Leitmineral kristallisierte mutmaßlich in nacheinanderfolgenden Zonen in zeitlicher Abfolge. Die Stärke der Metamorphose und der Deformation entsprachen sich weitgehend.
Résumé Des études sur les zones métamorphiques de type barrowien, entreprises dans des schistes essentiellement pélitiques à Singhbhum, Inde orientale, complètent la carte métamorphique de l'anticlinorium principal de Singhbhum. Les isogrades sont dirigées parallèllement aux axes de plis et se ferment là où ceux-ci montrent un plongement considérable. Dans cette zone, les minéraux-index de la zone la plus élevée ont succédé à la cristallisation des minéraux de degré inférieur dans leur ordre véritable. Un minéral index particulier a probablement cristallisé, au cours du temps, dans les zones inférieures successives. L'intensité du métamorphisme et de la déformation était dans les grands traits simultanée.
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8.
The geometry of the joint pattern in the Aywaille area (Ardennes, Belgium) is analysed with statistical methods. The orientations of intersecting joint-planes were recorded together with the bedding-plane. Four principal sets have been distinguished. These sets are related orthogonally to the bedding-plane and geometrically to the regional fold structure. All sets are considered to represent tensional structures, formed in a single period after the folding. The joint pattern is compared with a model given byPrice (1966). It is concluded that this model, describing the generation of joints in relation with folding, cannot explain completely the formation of the joint-sets under consideration here.
Zusammenfassung Die Geometrie des Klutgefüges im Aywaille Gebiet (Ardennen, Belgien) wurde mit statistischen Methoden analysiert. Die Orientierungen sich schneidender Kluften und der Schichtflächen wurden erfaßt und vier Hauptkluftscharen unterschieden. Diese Scharen durchsetzen die Schichtflächen im rechten Winkel und in Symmetrie zur Faltenachse. Alle Klüfte werden als gleichzeitig nach der Faltung entstandene Zugklüfte gedeutet, Das Kluftgefüge wird mit einem vonPrice (1966) angegebenen Modell für das Entstehen von Klüften nach der Faltung verglichen. Es ergibt sich, daß dieses Modell nicht zur vollständigen Erklärung der betrachten Kluftscharen ausreicht.
Résumé La géométrie du régime de fractures dans la région d'Aywaille (Ardennes, Belgique) est analysée par des méthodes statistiques. Les orientations des intersections des plans de fractures ont été enregistrées en inculant le plan de stratification. On a distingué quatre ensembles principaux. Ces ensembles sont reliés orthogonalement au plan de stratification et géométriquement au plissement régional. On considére que tous ces ensembles représentent des structures de traction, formées au cours d'une mème période postérieure au plissement. Ce type de fractures peut-être comparé au modèle donné par Price (1966). On peut en conclure que ce modèle, décrivant la formation des fractures associées au plissement, ne peut pas expliquer complètement le développement des ensembles de fractures étudiés ici.
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9.
I. Uysal M. B. Sadiklar M. Tarkian O. Karsli F. Aydin 《Mineralogy and Petrology》2005,83(3-4):219-242
Summary A large number of podiform chromitite bodies of massive, disseminated and nodular type have been located in ultramafic units, composed of depleted mantle harzburgite and dunite of the Marmaris Peridotite from Ortaca (Mula, SW Turkey). The chromite ore bodies are surrounded by dunite envelopes of variable thickness, exhibiting transitional boundaries to harzburgite host rocks. Chromitites, containing a large number of inclusions, i.e. silicates, base metal sulphides and alloys, and platinum-group minerals (PGM) have a wide range of chemical composition. The Cr# [Cr/(Cr+Al)] values of most chromitites are high (0.61–0.81) and Mg# [Mg/(Mg+Fe2+)] values range between 0.65 and 0.71 with TiO2 content lower than 0.24wt.%, which may reflect the crystallization of chromites from boninitic magmas in supra-subduction setting environment.Platinum-group minerals (PGM) such as laurite, erlichmanite and Os–Ir alloys, silicates such as olivine, clinopyroxene and amphibole, and base metal sulphides (BM-S), alloys (BM-A) and arsenides (BM-As) are found as inclusions in chromite or in the serpentine matrix. Platinum-group element (PGE) concentrations of the Ortaca chromitites (OC) are low in all samples. Total PGE (Ir+Ru+Rh+Pt+Pd) ranges from 63ng/g to 266ng/g and Pd/Ir ratios range between 0.23 and 4.75. PGE content is higher and the Pd/Ir ratio lower in Cr-rich chromitites compared to Al-rich ones. There is a strong negative correlation between the Cr# and Pd/Ir ratios (r=–0.930). The PGE patterns show a negative slope from Ru to Pt and a positive slope from Pt to Pd. The low PGE content in the majority of the OC may reflect a lack of sulphur saturation during an early stage of their crystallization. The laurite compositions show a wide range of Ru–Os substitution caused by relatively low temperature and increasing f(S2) during the chromite crystallization. The high Cr# of and hydrous silicate mineral inclusions in chromite imply that chromite crystallized in a supra-subduction setting. 相似文献
10.
Summary The provenance of the Mid-Devonian clastic sediments in the Teplá-Barrandian Unit (TBU) of the Bohemian Massif was investigated by laser ablation ICP-MS U–Pb zircon dating, bulk sediment geochemistry and mineralogical study of the heavy mineral fraction. In contrast to the island arc provenance of the TBU Neoproterozoic sediments, the Early Palaeozoic sediments contain significant amounts of differentiated crustal material. The detrital zircon populations in the Barrandian Mid-Devonian siltstones and sandstones show ages ranging from Archaean (3.0Ga) to Early Palaeozoic (0.39Ga). Major age maxima are at 2.6Ga, 2.0–2.25Ga, 0.62 and 0.51Ga. The youngest identified zircons so far correspond to Lower and Mid-Devonian ages. The extensive mechanical abrasion of zircons having Archaean (3.0, 2.8 and 2.6Ga) to Paleoproterozoic ages (2.25–2.0Ga) suggest their provenance from recycled old sedimentary sequences. The relatively large number of zircons with ages between 2.0 and 3.0Ga may indicate the presence of relicts of the Archaean/Paleoproterozoic crust in the source areas of the studied Mid-Devonian sediments. The absence of detrital zircon ages between 0.9 and 1.2Ga and the presence of zircon ages of 2.0–2.25 and 0.5–0.8Ga correspond to the zircon age pattern from the Gondwana-related North African, rather than Gondwana-related South American and Baltic terranes. The material was entering the basin predominantly from the west and consisted primarily of detrital material of Cambrian granitoids and recycled material of Neoproterozoic meta-sedimentary sequences. 相似文献
11.
Summary A detailed electron microprobe study of P, F, Ge and Ga-contents in rock-forming topaz was performed on a suite of Variscan granites at Podlesí in the western Kruné Hory Mts., Czech Republic. Topaz crystals from the relatively less evolved biotite- and protolithionite granites display homogeneous cathodo-luminescence (CL) intensities, whereas topaz from the marginal pegmatite, highly fractionated zinnwaldite granite and greisens show intense oscillatory zoning. Phosphorus contents reach 1.15wt% P2O5 in topaz from the zinnwaldite granite. Many topaz crystals are distinctly zoned with a maximum P content in the transition zone between core and rim. Phosphorus is incorporated into the topaz lattice by berlinite substitution: Al3++P5+=Si4++Si4+. The majority of analysed topazes are highly saturated in F, reaching 90–97% of the theoretical maximum saturation. Topaz from the marginal pegmatite only reaches 87–90% of F-saturation. There is a positive correlation between Ptopaz and Pwhole rock, but no correlation between Ftopaz and Fwhole rock. No difference has been found in P and F contents between magmatic and the hydrothermal (=greisen stage) topaz. Contents of Ge and Ga vary from around the detection limit (50ppm) up to 200ppm Ge and 100ppm Ga, respectively. 相似文献
12.
Dr. W. M. Bausch 《International Journal of Earth Sciences》1978,67(2):389-400
The main result of a field survey is the presentation of a petrographical map, which for the first time gives details of the main structures of the Jebel Nefusa volcano. A second result of the mapping is that obviously the age relationship between two of the major rock types — phonolites and flood basalts — needs revision: the phonolites are the oldest ones. - Also are given some preliminary remarks regarding mineralogical composition: flood basalts are characterized by olivines corroded and partly oxidized before final crystallization, and all phonolites contain appreciable amounts of analcite.
Zusammenfassung Es wird eine petrographische Übersichtskarte vorgelegt, welche erstmals die beherrschenden Strukturen im Aufbau des Jebel-Nefusa-Vulkans (nördl. Tripolitanien, Libyen) erkennen läßt. Ein Ergebnis der Kartierung ist eine Neugliederung der Altersabfolge der drei Haupt-Gesteinsgruppen Phonolithe — Flutbasalte — Melabasalte. Die Phonolithe müssen offensichtlich älter als die Flutbasalte sein, und sind wahrscheinlich die ältesten Glieder der Abfolge. — Vorab mitgeteilte petrographische Details: die Flutbasalte werden durch Olivine charakterisiert, welche schon vor der Erstarrung der Schmelze korrodiert und teiloxidiert worden waren, und die Phonolithe führen sämtlich erhebliche Anteile an Analcim.
Résumé Le résultat principal de cette recherche sur le terrain est présentation d'une carte pétrographique qui, pour la première fois, montre les détails de la structure principale du volcan Jebel Nefusa. Ce travail montre avec évidence que les relations d'âge entre deux des principaux types de roches, les phonolites et les épanchements basaltiques, appellent une révision, car les phonolites sont les plus anciennes. Quelques remarques sont faites sur la composition minéralogique: les épanchements de basaltes sont caracterisés par des olivines corrodées et en partie oxydées avant la cristallisation finale; toutes les phonolites contiennent de l'analcime en proportions appréciables.
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13.
Summary The Ni–Cu–Platinum Group Element (PGE) sulfide deposits of the Sudbury Structure have provided a major portion of the worlds total nickel production and their host rocks have been the subject of numerous research studies, yet a number of perplexing problems remain to be solved. On the one hand, studies seeking to explain the formation of the Sudbury Structure have now converged on a genetic model which proposes that the Main Mass and Offset Dykes of the Sudbury Igneous Complex (SIC) were produced by crystallization of an impact-generated melt sheet. On the other hand, these models have yet to be fully reconciled with the production of the very large volume of magmatic Ni, Cu, Co, and PGE-rich sulfide mineralization and the associated mafic rock types. This paper explores this problem using new precious metal data from the Main Mass and Offset Dykes. These data are used to understand the relationships between these rocks, and to provide constraints on how the Ni–Cu–PGE sulfide ore deposits fit into the geological evolution of the Sudbury Structure.In the two drill cores selected for study in this project, the Mafic Norite has 1–5 modal percent pyrrhotite plus chalcopyrite, and elevated Ni (40–1000ppm), Cu (40–1140ppm), and PGE (1.9–7.8ppb Pd, 1.8–7.3ppb Pt); this is overlain by Felsic Norite that contains pyrrhotite, and has a wide range in concentration of Ni (13–257ppm), Cu (7–328ppm), and PGE (<0.01–6.4ppb Pd, <0.01–5ppb Pt). For a similar range of MgO, the upper portion of the Felsic Norite unit has 5–10 times lower Ni and Cu abundances than within-plate basalts and local crustal rocks, and PGE abundance levels are mostly below analytical determination limits. Stratigraphic studies of other compositional profiles around the SIC demonstrate that this depletion signature of Ni, Cu, and PGE is widespread and developed not only above mineralized embayments and offsets, but also above barren sections of the lower contact of the SIC.The depletion of the upper part of the Felsic Norite in Ni, Cu and PGE is presumably due to equilibration of the magma with magmatic sulfide, and accumulation of this dense sulfide liquid. Results of modeling indicate that the parental magma giving rise to the Mafic and Felsic Norites had initial Ni and Cu contents of 210 and 110ppm, respectively. In addition, Ni, Cu and PGE tenors calculated in 100% sulfide from the Copper Cliff Offset average 13% Cu, 6% Ni, 18ppm Pd, and 19ppm Pt indicating that these sulfides had formed by fractionation from magmas that contained 310ppm Ni, 310ppm Cu, 18ppb Pd and 19ppb Pt. These values are factors of 3 to 5 higher than the Ni, Cu, Pd, and Pt contents of the Onaping Formation with average values of 55ppm Ni, 48ppm Cu, and 4.9ppb Pd as well as the marginal sulfide-poor phase of the Worthington Offset quartz diorite, which has average values of 61ppm Ni, 59ppm Cu, 2.8ppb Pd and 4.0ppb Pt. Both the Onaping Formation and the marginal quartz diorite are believed to represent the initial composition of a large component of the melt sheet. There is therefore a fundamental problem in reconciling the initial metal contents of the SIC magma as indicated by the marginal phases of the Offset dykes and that of the Onaping Formation with the composition of the SIC magma at the times of formation of the sulfides as indicated by their Ni, Cu and PGE tenors.It is proposed that because the SIC melt sheet was initially superheated with a temperature of 1700°C, it was able to dissolve 5 times as much S as it could at its liquidus temperature of 1200°C. It was also initially composed of an emulsion of mafic and felsic melts (Marsh and Zieg, 1999), which may have formed discrete magma cells. As the temperature of the melt sheet decreased, some of these magma cells became S-saturated and the resultant Ni–Cu–PGE sulfides settled downwards and on reaching magma cells lower in the melt sheet were re-dissolved thereby raising the Ni, Cu and PGE contents of the lower magma cells. It was from these enriched magma cells that precipitation of the ore-forming Ni–Cu–PGE sulfide melts eventually took place.The mineral potential of Offset and embayment structures appears to be empirically linked to the thickness of the overlying noritic rocks; for example, the most heavily mineralized embayments and Offset Dykes are located in areas where the Felsic Norite is thickest. It appears unlikely that the entire 1–3km-thick melt sheet was convectively mixing throughout its lateral extent, and so the heterogeneity in sulfide distribution was retained after crystallization and cooling. 相似文献
14.
Summary Geochemical data for 870 ore samples of 14 nickel sulphide (NiS) deposits from throughout the major Archaean Kambalda ore field, Western Australia, reveal highly heterogeneous Ni tenor (wt% Ni in 100wt% sulphide) variation that is difficult to explain solely by magmatic processes. The Ni tenor values for the deposits range from 6.2wt% Ni (Helmut deposit) to 19.7wt% Ni (Carnilya Hill deposit), close to the range for within single deposits (9.7–19.3wt% Ni). Contents of Ni and platinum-group elements (PGE) broadly increase with decreasing Fe and with increasing abundance of metamorphic pyrite+magnetite±silicates. In turn, the abundance of the metamorphic phases appears to be complexly related to structural setting, metamorphic grade, alteration type, and proximity to felsic intrusion. Chondrite-normalised multi-element plots of deposit compositions reveal relative depletions in Au, As, Bi, and Te.The relationship of increasing Ni content with secondary phase abundance indicates a strong role for metamorphic modification in the tenor variation. Replacement of pyrrhotite by pyrite+magnetite±chlorite during oxidation reduced the abundance of Fe sulphide relative to Ni sulphide and increased the Ni tenor of the residual sulphide. The extent of the oxidation reflects the extent of alteration fluid ingress along deformation structures and fabrics during talc-carbonate alteration, regional metamorphism, and felsic intrusion related to D3. The relative depletions of Au, As, Bi and Te combined with relative enrichments of these metals in nearby orogenic gold deposits mean that NiS deposits could represent metal reservoirs for Archaean gold hydrothermal systems. 相似文献
15.
Dr. Antonin Paluska Prof. Dr. Egon T. Degens 《International Journal of Earth Sciences》1979,68(1):284-301
The Quaternary geology of the Black Sea — Caspi region is reconstructed in a sequential series of maps. Over the past 400 000 years the total subsidence in the former shallow basins can be as high as 3 km, resulting in the Black Sea and Caspian deep basins of today with water depths ofca. 2000 and 1000 m, respectively. In relation to such dimensions, eustatic sea level changes have only a minor impact on bathymetry.
Zusammenfassung Die tektonische und paläogeographische Entwicklung im Schwarzmeer — Kaspi Gebiet während des Quartärs ist in einer zeitlich gestaffelten Serie von Karten dargestellt und erläutert. Absenkungen bis zu 3 km haben im Verlauf der letzten 400 000 Jahre aus altquartären Flachmeerbecken das heutige Schwarze und Kaspische Meer mit Wassertiefen von ca. 2000 bzw. 1000 m geprägt. Gemessen an dieser Größe sind die durch eustatische Meeresspiegelschwankungen verursachten Veränderungen der Bathymetrie unbedeutend.
Résumé La géologie quaternaire de la région Mer Noire — Caspienne a été représentée dans une série de cartes successives; depuis 400 000 ans l'affaissement total dans ces bassins, à l'origine peu profonds, est important: jusqu'à 3 km. En conséquence, les bassins des Mers Noire et Caspienne sont profonds, avec des bathymétries d'environ 2000 et 1000 m respectivement. En comparaison, les variations eustatiques d'ordre climatique sont mineures.
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16.
Dozent Dr. Lothar Greiling 《International Journal of Earth Sciences》1967,56(1):336-340
Zusammenfassung Kalkknollengesteine können in Eugeosynklinalen innerhalb von Rutschmassen, durch Beben, durch unterschiedliche Setzung und durch sedimentäre Boudinage entstehen. Daran gebunden sind syndiagenetische Zerbrechung und örtlich intensive syndiagenetische Faltung.Die mesozoischen Kalk-Mergel-Folgen der Miogeosynklinalen und der Innenbecken sind über weite Strecken dicht mit pseudonodules erfüllt. Die pseudonodules sind wahrscheinlich durch die Aufarbeitung einer älteren Schüttung durch eine jüngere Schüttung hervorgegangen. Vorausgesetzt wird ein unruhiges Relief infolge unterschiedlicher Setzung. Ein großer Teil der mesozoischen Kalke liegt auf zweiter Lagerstätte.
Rocks containing limestone nodules may develop in eugeosynclines within slump masses, by earthquakes, differential compaction and boudin-shaped sedimentary accumulations. Syndiagenetic fracturing and strongly developed syndiagenetic folding are related to these structures.Pseudonodules are densely distributed throughout extensive areas of the mesozoic limestone-marl series within the miogeosynklines and the interior basins. They probably resulted from the reworking of an older sediment. An uneven relief, produced by differential compaction can be assumed. A large portion of the mesozoic limestone occurs within this reworked type of deposit.
Résumé Il est possible que des calcaires noduleux se forment dans des eugéosynclines au milieu d'éboulements ou par des tremblements de terre ou par un tassement differencié ou bien par un boudinage sédimentaire. En relation avec ces phénomènes on trouve une tectonique syndiagénétique de style cassant et localement une tectonique syndiagénétique de plis intenses.Les successions calcaro-marneuses du Mésozoique des miogéosynclines ainsi que des bassins intérieurs contiennent bien des pseudonodules à longues distances. Il est probable que ces pseudonodules résultent de la reprise d'une ancienne par une nouvelle couche de sédimentation sous la condition d'un relief accentué à cause d'un tassement differencié. Une grande partie des calcaires mésozoiques se trouve maintenant en gîte secondaire.
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17.
Priv.-Doz. Dr. Manfred Schidlowski 《International Journal of Earth Sciences》1973,62(3):840-863
The economically important sulfide deposits of Precambrian age can be subdivided into two principal groups. The first group is represented by Ni- and Cu-bearing differentiates within either layered intrusions of the Sudbury-Bushveld type or within smaller ultramafic bodies (sometimes of greenstone belt association). The relatively narrow spread around the meteorite standard of the 34S values of these deposits suggests a mantle provenance of the sulfide sulfur.The second group (which is quantitatively more important) is represented by stratiform concentrations of base metal sulfides in sedimentary sequences lacking normally any ties to potentially ore-bearing magmas (Copper Belt, Broken Hill, Mount Isa, etc.). Although the problems related to the origin of such strata-bound deposits are rather complex, the majority of the latter probably formed as syngenetic sulfide precipitates in reducing aqueous environments characterized by the presence of bacteriogenic H2S. Sulfur isotope data furnished by some of the principal deposits actually suggest that hydrogen sulfide produced by bacterial sulfate reduction was instrumental in bringing about a precipitation of the metal sulfides, thus underlining the decisive role played by the biosphere in processes of supergene metal concentration.
Zusammenfassung Die wirtschaftlich wichtigen sulfidischen Metallkonzentrationen in präkambrischen Gesteinen lassen sich im wesentlichen zwei Lagerstättengruppen zuordnen. Die erste Gruppe bilden Ni- und Cu-führende sulfidische Differentiate in geschichteten Intrusionen vom Typ Sudbury-Bushveld oder innerhalb kleinerer ultrabasischer Komplexe. Die nur geringe Streubreite der 34S-Werte um den Meteoriten-Standard legt eine abyssische Herkunft des sulfidischen Materials (Magnetkies, Pentlandit, Kupferkies u. a.) derartiger Lagerstätten nahe.Die zweite und quantitativ wichtigere Gruppe bilden schichtige Anreicherungen von Buntmetallsulfiden in Sedimenten, die in der Regel keinerlei Beziehungen zu potentiell erzbringenden Magmatiten erkennen lassen (Copper Belt, Broken Hill, Mount Isa u. a.). Obwohl die beträchtlichen Probleme dieser stratiformen Sulfidlagerstätten eine genetische Deutung schwierig machen (und insbesondere die oft enorme Streubreite der Schwefelisotopen auf eine polygene Herkunft der Sulfide schließen läßt), dürfte es sich bei der Mehrzahl der Vorkommen um primär synsedimentäre Metallausfällungen in einem H2S-führenden reduzierenden Milieu handeln, wobei spätere tektonischmetamorphe Stoffmobilisierungen möglicherweise eine weitere Konzentration der Lagerstättensubstanz bewirkt haben. Die starke Beteiligung von bakteriogenem Schwefelwasserstoff bei der Ausfällung der Sulfide wird durch die Schwefelisotopen-Verteilung in verschiedenen derartigen Lagerstätten gestützt. Dieser Befund unterstreicht gleichzeitig die entscheidende Rolle der Biosphäre bei der Bildung von Metallanreicherungen im exogenen Zyklus.
Résumé Les concentrations de sulfures métalliques économiquement importantes dans les terrains précambriens peuvent essentiellement être subdivisées en deux groupes de gisements. Le premier groupe comprend les différenciats de sulfures nickelifères et cuprifères dans les intrusions litées du type Sudbury-Bushveld ou dans l'intérieur de complexes ultrabasiques plus petits. La faible distribution des valeurs du soufre 34 des météorites standard suggère une provenance abyssale des matériaux sulfurés de ces gisements (pyrrhotine, pentlandite, sulfures de Cu, etc.). Le deuxième groupe quantitativement plus important comprend les enrichissements «stratiformes »de sulfures métalliques dans les sédiments qui, en règle générale, ne montrent aucune liaison avec des magmatites potentiellement minéralisantes (Copper Belt, Broken Hill, Mount Isa, etc.). Quoique les problèmes importants relatifs à ces gisements sulfurés stratiformes rendent difficile une interprétation génétique (et en particulier la dispersion souvent énorme des isotopes du soufre qui permet de conclure à une provenance polygène des sulfures), il doit s'agir dans la plupart des cas de précipitations de métaux synsédimentaires primaires dans un milieu réducteur contenant H2S; à la suite de quoi une mobilisation ultérieure tectonico-métamorphique pourrait avoir exercé une nouvelle concentration de la matière du gisement. La forte participation d'H2S bactériogène au cours de la précipitation des sulfures est confirmée par la distribution des isotopes du soufre dans différents de ces gisements. Ce fait souligne simultanément le rôle décisif de la biosphère au cours de la formation des enrichissements métalliques dans le cycle exogène.
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18.
W.-L. Huang 《Mineralogy and Petrology》2003,79(3-4):243-258
Summary ¶This study experimentally investigated the transformation kinetics of synthetic polycrystalline aragonite to calcite at four temperature/pressure conditions (330°C/200MPa, 380°C/325MPa, 430°C/580MPa, and 480°C/875MPa), close to the calcite-aragonite equilibrium phase boundary. The extents of transformation measured as a function of time in a synthetic system, using in-situ annealed, high purity samples, are consistent with the kinetic model for grain-boundary nucleation and interface-controlled growth. The growth rates are slightly lower than those previously determined for a natural polycrystalline sample at 330 and 380°C. The activation energy (158kJ/mol) for calcite growth from synthetic samples is lower than that (247kJ/mol) from natural samples, but is close to the previously reported value (163kJ/mol) from a single crystal aragonite. The extrapolation of our experimental data to natural conditions reveals unusually fast transformation rates, in contrast to those of natural samples. The presence of deformational strain, fractures, defects or impurities in natural samples, and other factors may account for the discrepancy. This study suggests that the retrograde metamorphism of aragonite to calcite may proceed in a wide range of rates also depending on other geological factors than temperature and pressure.Received July 15, 2002; revised version accepted May 15, 2003 相似文献
19.
Dr. Edwin Kemper Dr. Hans Hermann Schmitz 《International Journal of Earth Sciences》1981,70(2):759-773
Zusammenfassung Glendonite sind Pseudomorphosen von überwiegend Calcit (in mehreren Generationen) nach Thenardit (Na2SO4). Die meistens sternförmigen Kristallaggregate von Walnuß- bis Faustgröße bildeten sich im unterkühlten Meereswasser (cold salinity currents) in oder auf der oberen Lage des Meeresbodens. Sie sind an marine Tonsteine gebunden und kommen in ihrem Verbreitungsgebiet in großer Zahl vor. Rezente Glendonite treten nur im Arktischen Ozean und seinen Nebenmeeren (Weißes Meer) auf. Fossile gibt es in Perm und Kreide Australiens (permisches Vereisungsgebiet) und in den jeweils hohen Breiten der Nordhalbkugel im Domerium, mittleren Jura, Valangin, Ober-Apt/Unter-Alb, Oligozän/Miozän und Pleistozän/Holozän. Für diese Zeiten ist eine erhebliche Abkühlung zu postulieren.Beim Vergleich mit den entsprechenden Schichtenfolgen Mitteleuropas fällt auf, daß in den Zeiten der Glendonit-Vorkommen der arktischen Gebiete im borealen Europa dunkle Tonsteine abgelagert wurden. In Zeiten starker Kalksedimentation (Ober-Oxford, Kimmeridge, Ober-Kreide) und arider oder subtropischer Klimate in Mitteleuropa (Tithon: Münder Mergel-Fazies und Berrias: Wealden-Fazies) fehlen Glendonite auch im hohen Norden.Alle diese Befunde verweisen auf ausgeprägte, langfristige Klimaschwankungen vom Lias ab. Zur Zeit der kälteren Phasen müssen in den hohen Breiten mit den heutigen Verhältnissen vergleichbare polare Klimate geherrscht haben.
Glendonites are pseudomorphs of mainly calcite (in several generations) after Thenardit (Na2SO4). The crystal aggregates are preponderantly star shaped and range in size between walnut and fist dimensions. They were formed by cold salinity currents in the uppermost layer of the ocean floor. They are restricted to marine shales and mudstones and occur in great quantities in their area of distribution. Recent glendonites are known only from the Arctic Ocean and adjacent seas (e. g. the White Sea). Fossil glendonites occur in the Permian and Cretaceous of Australia (Permian area of glaciation) and in high latitudes of the Northern hemisphere in the Domerian, middle Jurassic, Valanginian, late Aptian — early Albian, Oligocene — Miocene, and Pleistocene — Holocene. For these periods a considerable cooling has to be postulated.If the sediments of these periods are compared with the corresponding ones of central Europe it is obvious that in those periods during which glendonites were formed in high latitudes dark shales were deposited in the boreal part of Europe. In periods of high lime accumulation (Upper Oxfordian, Kimmeridgian, Upper Cretaceous) and arid or subtropical climates in central Europe (e. g. the Münder Mergel facies of the Tithonian and the Purbeck and Wealden facies of the Berriasian) glendonites are absent from the high latitudes.All these observations point to intensive and long term variations of climate from the early Jurassic on. During the cold phases, comparable polar climates must have predominated in the high latitudes as exist today.
Résumé Les glendonites sont des pseudomorphoses, principalement de calcite (en plusieurs générations), de thénardite (Na2SO4). Les agrégats, le plus souvent de forme radiée, de la taille d'une noix à celle du poing, se sont formés dans de l'eau marine surrefroidie (»courants de salinité froide«) dans la couches supérieure des fonds marins ou à sa surface. Ils sont liés à des argiles marines et se présentent en grande quantité dans leur aire d'extension. Les glendonites récentes se rencontrent seulement dans l'Océan arctique et dans les mers annexes (Mer blanche). Elles existent à l'état fossile dans le Permien et le Crétacique de l'Australie (région de la glaciation permienne) et dans les hautes latitudes de l'époque de l'hémisphère nord dans le Domérien, le Jurassique moyen, le Valanginien, l'Aptien supérieur/inférieur, l'Oligocène/Miocène, et le Pleistocène/Holocène. Pour ces périodes il y a lieu de postuler un net refroidissement.Par comparaison avec les séries correspondantes de l'Europe centrale, il apparaît que des argiles foncées ont été déposées, lors des occurrences de Glendonites des régions arctique, dans l'Europe boréale. Lors de sédimentations calcaires intenses (Oxfordien supérieur, Kimméridgien, Crétacique supérieur) et dans les climats arides ou subtropicaux dans l'Europe centrale (Tithonique: facies marneux de Münder, et Berriasien: facies wealdien) les glendonites sont absentes également dans les hautes latitudes septentrionales.Toutes ces occurrences indiquent des modifications climatiques bien marquées, de longue durée à partir du Lias. Au moment des phases plus froides, il a dû régner dans les hautes latitudes un climat polaire comparable à celui de nos jours.
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20.
I. Peytcheva A. von Quadt M. Ovtcharova R. Handler F. Neubauer E. Salnikova Y. Kostitsyn S. Sarov K. Kolcheva 《Mineralogy and Petrology》2004,82(1-2):1-31
Summary Geochronological data (U–Pb, Rb–Sr and 40Ar/39Ar) are used to unravel the Late Alpine high-grade metamorphism, migmatisation and exhumation of Variscan granitoids within the core of the Central Rhodopean dome, Bulgaria. The age of the granitoid protolith is 300±11Ma, as determined by U–Pb analyses on single zircons selected from the core of the dome structure.Rb–Sr whole rock data define an errorchron with a large scatter of the data points due to the Late Alpine metamorphic overprint. The slope of the reference line indicates a Variscan magmatic event. Strontium characteristics are used to discriminate the samples most influenced by metamorphism from those, which reflect possible differences in the protolith age of the granitoids.Petrological-geochemical data, the initial strontium ratio of 0.708±0.001, and Hf zircon values ranging from –2.58 to –3.82 point to a mixed, but crust-dominated origin of the Variscan magmas; young crustal material and mantle fragments were sources for the I-type metagranitoids.The exhumation of the granitoids from depths greater than 20–25km to about 5km below the surface was a rapid geological process. It started with the formation of granitic eutectic minimum melts at the temperature peak of metamorphism. Monazite crystallisation at about 650°C continued during isothermal decompression to possible depths of about 10–12km. An age of 35.83±0.40Ma was determined using conventional U–Pb isotope methods on four multigrain monazite fractions. A maximum average age of 36.6–37.5Ma (assuming same error uncertainties) for crystallisation of the metamorphic monazites was calculated assuming 10 to 20% monazite resetting during the subsequent Oligocene volcanism and hydrothermal activity in the region of the Central Rhodopean Dome. The rocks were then cooled to about 350–300°C at 35.35±0.22Ma according to 40Ar/39Ar ages of biotites and below 300°C at 35.31±0.25Ma (Rb–Sr data), as indicated by crystallisation of adularia in an open vein subsequent to pegmatite intrusion. A minimum exhumation rate of 3–5km per 1 million years can therefore be calculated for the exhumation of the metagranitoids during the period from 38–35Ma. 相似文献