37 research outputs found
Behavior of basic refractories at high temperatures in steelmaking processes thermodynamics and implications for the usability of olivine as refractory material
No full textOxygen and hydrogen isotopes at DSDP Leg 65 Holes
No full textIn order to provide information on the degree of alteration of the very young basaltic basement drilled on Leg 65 in the mouth of the Gulf of California, we have measured the oxygen isotopic composition of whole rocks and mineral separates. Considerable data already exist for older ocean crust, in particular for the deep holes drilled in the Atlantic Ocean on Deep Sea Drilling Project (DSDP) Legs 37, 45, 46, and 51-53. These data indicate that in all of these holes, which include crust as young as 3.5 m.y. old, a significant amount of alteration has taken place as the result of low-temperature interaction between basalt and seawater (cf. Muehlenbachs, 1977, 1980; Hoernes et al., 1978; Friedrichsen and Hoernes, 1980). It is therefore of interest to determine whether Leg 65 crust, which is only 0.5 to 1.5 m.y. old, has experienced a similar degree of alteration
Stable oxygen isotopes - A new approach for tracing the origin of oxide inclusions in steels
No full textPrimitive high-Mg andesites from the Western Alps, Italy: Products of interaction of sediment diapir derived melts with mantle-wedge peridotite in a continental collision zone
No full text(Table 2) Hydrogen isotopes for selected whole rock samples at DSDP Leg 65 Holes
No full text(Table 2) Hydrogen isotopes for selected whole rock samples at DSDP Leg 65 Hole
(Table 1) Oxygen isotopes for whole rock samples and mineral separates DSDP Leg 65 Holes
No full text(Table 1) Oxygen isotopes for whole rock samples and mineral separates DSDP Leg 65 Hole
Rekonstruktion von Metamorphosepfaden mit stabilen Isotopen : Möglichkeiten der Laserfluorinierung am Beispiel des Sächsischen Granulitgebirges
No full textDiese Arbeit beschäftigt sich mit der Analyse von Sauerstoffisotopen und der Auswertung und Interpretation der bestimmten Gleich- bzw. Ungleichgewichte. Ein wesentlicher Schwerpunkt der Arbeit liegt auf der Bestimmung von peaknahen Metamorphosetemperaturen. Es wird eine Methode angewendet, die es ermöglicht, aus den Fraktionierungskoeffizienten des Gesamtgesteins und mindestens einer Phase, die für Sauerstoff eine hohe Schließtemperatur hat, solche peakmetamorphen Temperaturen zu ermitteln. Dies geschieht mit Hilfe von Fraktionierungs-Plots, bei denen die Fraktionierungskoeffizienten aller Phasen und vom Gesamtgestein gegen den gemessenen d18O-Wert aufgetragen werden. Im Falle eines Gleichgewichts befinden sich alle Phasen auf einer Geraden. Aus der Steigung der Geraden können für die hier untersuchten Granulite des Sächsischen Granulitgebirges Temperaturen der granulitfaziellen Metamorphose von über 1000°C nachgewiesen werden. Allerdings kommt es in den meisten Gesteinen durch retrograde Diffusion zu einer partiellen Rücksetzung der Isotopengleichgewichte. Aus diesen Ungleichgewichten wurden im Rahmen dieser Arbeit Abkühlraten für die Granulite und für einen Granatgneis des Kordieritgneis-Komplexes iterativ berechnet. Die Abkühlraten liegen zwischen 50 und 80 °C/Ma für die Granulite. Die hier erzielten Ergebnisse werden durch unabhängige Methoden bestätigt. Mit diesen Daten kann ein Beitrag zur Klärung der thermischen Entwicklung und der Hebungsgeschichte eines kontinentalen Krustensegmentes geleistet werden. Es kann gezeigt werden, dass die Granulite einem fast isothermalen Dekompressionspfad folgen. Die für diese Untersuchungen verwendete analytische Methode ist die der Laserfluorinierung in Kombination mit irm-Massenspektrometrie. Zum einen wurden die Untersuchungen an Mineralseparaten, zum anderen wurden In-Situ-Analysen an etwa 2 mm dicken Gesteinsstücken oder großen Einzelkörnern durchgeführt. Daraus ergibt sich ein weiterer Schwerpunkt dieser Arbeit, der sich mit der Weiterentwicklung der Methode der Laserfluorinierung beschäftigt hat. Es ging um die Eliminierung störender Einflüsse, Reduktion der Probenmengen und eine Verbesserung der Reproduzierbarkeit von Analysen. Die In-Situ Analysen dienten zur Untersuchung der O-Isotopen Homogenität der Proben und im Fall eines Granatperidotits zur Klärung der Herkunft des Gesteins. So konnte für die Granulite eindeutig eine homogene O-Isotopen-Verteilung für Granat nachgewiesen werden, wohingegen für einen Granatgneis des aufgelagerten Cordieritgneis-Komplexes starke Inhomogenitäten, teilweise sogar innerhalb eines Korns, nachgewiesen wurden. Die Untersuchungen großer, einzelner Granate aus einem zwischengelagerten Peridotit belegen eine Mantelisotopie
Reconstruction of sedimentary environment and climate conditions by multi-geochemical investigations of Late Palaeozoic glacial to postglacial sedimentary sequences from SW-Gondwana
No full textThe most extensive Phanerozoic glaciation and its termination occurred during the Carboniferous-Permian on the southern hemispherical Gondwana supercontinent. This thesis aims to provide detailed geochemical analyses of the lower Karoo Supergroup sediments in southwestern Gondwana with focus on the Karoo Basin in South Africa. Additional samples derive from the Paraná Basin (Brazil), Kalahari Basin (Botswana), and Warmbad Basin (Namibia). Multiple geochemical investigations (element-geochemical, organic-geochemical and isotope data) were supported by mineralogical data. By this multi proxy approach, information about sedimentary environment, climate conditions, and postsedimentary processes can be obtained. orbital frequencyElement geochemical proxies (CIA, Zr/Ti, Rb/K, V/Cr) record three confined shifts in climate and paleoenvironment of the Karoo Basin during deposition of the glacial Dwyka Group. These shifts were induced by changes in sea level, weathering rate, provenance, and redox conditions. Organic geochemical investigations (Corg, C/N, lipid biomarkers) indicate the organic matter in the central Karoo Basin was primarily of algal origin. In agreement with element proxies, the varying δ13Corg, values mirror shifts in pCO2, rather than variations of organic-matter type. A covariation trend between carbon isotope signatures of equatorial carbonates and δ13Corg, values from the Karoo Basin argues against local forcing factors and instead implies a global climate-control mechanism. The 5-7 m.y. duration of a complete glacial cycle is not in tune with any known orbital frequency. The onset of the postglacial phase (Ecca Group) is characterized by significant changes in sedimentary environments. Predominantly fully marine conditions prevailed and the formation of anoxic conditions is indicated by the occurrence of Corg, rich sediments containing mineral phases such as apatite and pyrite. Comparable proxy signals are obtained from localities within the Karoo Basin and from the Warmbad Basin in Namibia. Especially the accumulation of phosphatic sediments points to high bioproductivity due to elevated nutrient supply. At the basin borders (Witbank Basin), in terrestrially dominated sedimentary environments, the onset of postglacial climate conditions was recorded by significant changes in the organic matter composition. The Dwyka/Ecca boundary coincides with a progressional temperature rise. Favourable climate conditions led to the spread of the Glossopteris flora. High chemical weathering rates, assumedly fast growing vegetation and the documented reptile fauna (Mesosaurus), indicate warm-humid climate conditions during the Early to Middle Permian in south Gondwana. During the Middle to Late Permian the continuous retreat of former marine sedimentary environments commences. Turbiditic deposits were replaced by deltaic basin fills, which were in tune covered by fluvial and lacustrine sediments. The retreat of marine conditions in the Karoo Basin was closely related to the rising Cape Fold Belt, whereby the connection to the Panthalassic Ocean was finally terminated. Arid climate conditions during the Late Permian and Lower Triassic are indicated by redbeds and aeolian deposits of the upper Beaufort and Stormberg/Lebung Groups
Trace element and isotopic (Sr, Nd, Pb, O) arguments for a mid-crustal origin of Pan-African garnet-bearing S-type granites from the Damara orogen (Namibia)
No full textGeochronological data, major and trace element abundances, Nd and Sr isotope ratios, δ18O whole rock values and Pb isotope ratios from leached feldspars are presented for garnet-bearing granites (locality at Oetmoed and outcrop 10 km north of Omaruru) from the Damara Belt (Namibia). For the granites from outcrop 10 km N′ Omaruru, reversely discordant U–Pb monazite data give 207Pb/235U ages of 511±2 Ma and 517±2 Ma, similar to previously published estimates for the time of regional high grade metamorphism in the Central Zone. Based on textural and compositional variations, garnets from these granites are inferred to be refractory residues from partial melting in the deep crust. Because P–T estimates from these xenocrystic garnets are significantly higher (800°C/9–10 kbar) than regional estimates (700°C/5 kbar), the monazite ages are interpreted to date the peak of regional metamorphism in the source of the granites. Sm–Nd garnet–whole rock ages are between ∼500 and ∼490 Ma indicating the age of extraction of the granites from their deep crustal sources. For the granites from Oetmoed, both Sm–Nd and Pb–Pb ages obtained on igneous garnets range from ∼500 to ∼490 Ma. These ages are interpreted as emplacement ages and are significantly younger than the previously proposed age of ∼520 Ma for these granites based on Rb/Sr whole rock age determinations. Major and trace element compositions indicate that the granites are moderately to strongly peraluminous S-type granites. High initial 87Sr/86Sr ratios (>0.716), high δ18O values of >13.8‰, negative initial εNd values between −4 and −7 and evolved Pb isotope ratios indicate formation of the granites by anatexis of mid-crustal rocks similar to the exposed metapelites into which they intruded. The large range of Pb isotope ratios and the lack of correlation between Pb isotope ratios and Nd and Sr isotope ratios indicate heterogeneity of the involved crustal rocks. Evidence for the involvement of isotopically highly evolved lower crust is scarce and the influence of a depleted mantle component is unlikely. The crustal heating events that produced these granites might have been caused by crustal thickening and thrusting of crustal sheets enriched in heat-producing elements. Very limited fluxing of volatiles from underthrust low- to medium-grade metasedimentary rocks may have also been a factor in promoting partial melting. Furthermore, delamination of the lithospheric mantle and uprise of hot mantle could have caused localized high-T regions. The presence of coeval A-type granites at Oetmoed that have been derived at least in part from a mantle source supports this model
Tracing the origin of oxide inclusions in continuously casted steel using stable oxygen isotopes : An interdisciplinary approach
No full textA detailed mineralogical, chemical, and isotope study was conducted on refractories and slags used in the continuous casting steelmaking process. The aim of this study was to trace the origin of non-metallic inclusions and SEN-precipitates (clogging) in continuously casted steels. It was especially focussed on the thermochemical behaviour of basic sprayable disposable tundish lining, which are composed of forsteritic olivine and periclase. The results of the mineralogical study clearly indicated that the fayalite component of the forsteritic olivine is reduced to iron metal. Ferrous iron is substituted by Mg 0 , which is released by evaporation of periclase at high temperatures and reducing conditions. The periclase evaporating reaction also released oxygen gas. The oxygen isotope composition as measured in SEN-precipitates match the isotope composition of the periclase. It was therefore concluded that periclase in conjunction with olivine may be, at least partly, responsible for the formation of non-metallic inclusions in low alloyed, Al-killed, and continuously casted steels. Manganese occured in concentrations up to 1.3 wt.% in the casted steel melts. Mn leaves the steel melt and infiltrates the silica-rich tundish slag as well as the tundish lining. The result are high Mn-concentrations in the tundish slag and the formation of tephroititc olivine in the tundish lining. Spinel forms where tundish slag infiltrated the tundish lining. Corrosion of forsteritic olivine in the tundish lining by slag was never observed, but overgrowths of Mn-rich olvine over forsterite was abundant
