ALBERT

Description: Trees, as long living plants, are governed by environmental and/or climate changes within their habitat. Their growth rings record to a large extent the temporal dynamics of these changes either directly or through tree physiological reactions. They render the highest time resolution thus far possible for environmental or climate reconstructions of the past 10,000 years (exactly dated, annually resolved, see: [828], [994]). Trees are a substantial part of the human environment with a high socio-economic value. Their large geographical extension over various regions of the world, including those with greatest population densities but also marginal areas allows to gain unique informations about local and regional consequences of global climate change.

Description: Die im Norddeutschen Becken vorkommenden hochsalinaren, heißen Tiefenwässer besitzen ein beträchtliches Wärmepotential, das bisher in Neustadt-Glewe, Neubrandenburg und Waren zur Energiegewinnung genutzt wird. Das Ziel der vorliegenden Arbeit bestand zum einen darin, die Herkunft und die Genese dieser Solen und der in ihnen gelösten Stoffe zu rekonstruieren. Ein zweiter Schwerpunkt bestand in der Ermittlung geochemischer Parameter, die für einen problemlosen Langzeitbetrieb geothermischer Anlagen und somit für deren Wirtschaftlichkeit von Bedeutung sind. Die untersuchten Solen stammten aus Aquiferen, die durch fünf Bohrungen (Neubrandenburg, Waren, Rheinsberg, Neustadt-Glewe, Hamburg-Allermöhe) in Tiefen von 1250 bis 3250 m (54 bis l28°C) erschlossen wurden. Alle untersuchten Na-Cl-Solen wurden aus Sandsteinaquiferen des Keuper (Contorta!Postera-Schichten) gefördert, für die mit zunehmender Tiefe steigende TDS-Gehalte (134 bis 224 g/1) charakteristisch sind. Die Zusammensetzung der gelösten Feststoffe blieb über einen Zeitraum von 3 Jahren konstant. Die Br/CJ-Verhältnisse der Solen sind kleiner als in eingedampftem Meerwasser. Dies und 811B-Werte von +23.8 %o bis +36.3 %o indizieren die Herkunft des Salzgehaltes durch Auflösung/Laugung von Salzen. Das Gas-Wasser-Volumenverhältnis in Proben geothermisch genutzter Solen liegt bei max. 1:10. Die Gasphase wird von C02, N2 und CH4 dominiert, wobei der Gehalt an C02 und CH4 mit der Tiefe zunimmt. Als Spurengase treten He, Ar, H2 und weitere Kohlenwasserstoffe auf (jeweils 〈1 Vol.-%). Die Gasphase des Thermalwassers Neustadt-Giewe zeigte über einen Zeitraum von 2 Jahren keine Änderung in ihrer Zusammensetzung. Periodische Schwankungen in sehr kleinen Konzentrationsbereichen während einer mehrtägigen Gasmeßkampagne korrelieren mit den Erdgezeiten. Die N2-Ar-He-Verhältnisse zeigen, daß es sich um tiefzirkulierende Oberflächenwässer handelt. Untermauert wird diese Interpretation durch die sehr niedrigen 3HefHe-Verhältnisse (R!Ra:S;O.Ol), die keine Mantelheliumkomponente anzeigen, sowie die gegenüber Luft (295.5) leicht erhöhten 40 Ar/36 Ar-Verhältnisse von bis zu 367.5. He-Akkumulationsalter als scheinbare Verweildauer der Solen von 20 bis 50 Ma wurden berechnet. Das Tiefenwasser von NeustadtGiewe besaß gegenüber den anderen Lokationen erhöhte Kohlenwasserstoffgehalte. Die 813C1,2,3- Werte weisen auf thermogenetische Kohlenwasserstoffe und auf ein marines Ausgangsmaterial mit einer Reife, die einer Vitrinitreflektion von etwa 1.2 % entspricht, hin. Die Herkunft aus Corgreichen Zechstein-Sedimenten ist wahrscheinlich, organisches Material des wesentlich tiefer liegenden Karbons scheidet als Quelle aus. Die 8180- und öD-Werte der Wässer zeigen an, daß meteorisches Wasser bei der Genese eine bedeutende Rolle gespielt hat. Die ermittelte isatopische Zusammensetzung der meteorischen Komponente weicht von heutigen Niederschlagswässern ab und weist einen letztmaligen Kontakt mit der Atmosphäre zu einer Zeit deutlich wärmeren Klimas als das heutige nach. Die in einem Thermalwasser vorhandenen Gase können die technologische Eignung der Sole und den Betrieb einer geothermischen Anlage maßgeblich beinflussen (Scaling, Auftreten brennbarer Gase, Entlösung von Gasen). Bei Vorhandensein Corg-reicher Sedimente nimmt die Wahrscheinlichkeit des Auftretens brennbarer Gase in Wässern aus größerer Tiefe, die durch ihre höhere Temperatur wirtschaftlicher sind, zu. Um die Entgasung eines Tiefenwassers innerhalb einer Anlage zu verhindem und somit Scaling und unkontrolliertes Entgasen zu minimieren, wurde anhand Literaturdaten exemplarisch für den Thermalwasserkreislauf der Anlage Neustadt-Giewe (Sole mit den höchsten Gasgehalten) ein Mindestanlagendruck berechnet. Danach sind etwa 2 bar ausreichend, um ein Entgasen der Sole zu verhindern; Strömungseffekte erfordern jedoch eine Erhöhung des Anlagendrucks auf etwa 4 bar. Die zeitliche Konstanz in der Zusammensetzung der gelösten Feststoffe und der Gasphase über einen Zeitraum von 2 bzw. 3 Jahren zeugt von einer relativ großen räumlichen Homogenität der Aquifere, wodurch der Betrieb der Anlagen durch Änderungen in der chemischen Zusammensetzung der Solen kaum gefährdet zu sein scheint. Die Ergebnisse der vorliegenden Arbeit haben gezeigt, daß sowohl bei der hydrodynamischen Vorerkundung als auch während des Betriebes eines geothermischen Heizwerkes die genaue Kenntnis der Gasmengen und der Gaszusammensetzung von entscheidender Bedeutung ist.

Description: Deep seated hydrothermal brines in the North German Basin have a considerable heat potential, which is currently used for geothermal energy recovery in Neustadt-Glewe, Neubrandenburg and Waren. One aim of this study was to reconstruct the origin of these brines and their dissolved substances. Another goalwas to determine geochemical parameters which are critically influence the long-term operation, and hence the econornic viability of geothermal plants. The brines come from aquifers which have been accessed by 5 boreholes (Neubrandenburg, Waren, Rheinsberg, Neustadt-Glewe, Hamburg-Allermöhe) in depths from 1250 to 3250 m (54 to 128 °C). All investigated Na-Cl-brines were produced from sandstone aquifers of the Keuper (Contorta!Postera layers). Typically, TDS-values (134 to 224 g/1) increase with depth. The compositions of the dissolved solids were constant during 3 years. The Br/Cl ratios of the brines are lower than evaporated sea water. This, and 811B-values of +23.8 %o up to +36.3 %o indicate dissolution/leaching of salt as the origin of the salt content. The gas-water volume ratio of samples from brines used for geothermal energy recovery are less than around 1:10. The gas phase is dorninated by C02, N2 and C~ with higher C02- and C~ contents with increasing depths. He, Ar, H2 and other hydrocarbons exist as traces ( 〈1 vol.% each). The gas phase of the thermal water from Neustadt-Giewe showed no changes in its composition during 2 years. Small · periodical variations in the concentrations obtained from gas monitaring over several days correlate with the earth tides. The N2-Ar-He ratios show that the waters are deep-circulating meteoric waters. This interpretation is supported by very low 3HefHe ratios (R!Ra:S;O.Ol), which show no mantle helium, and 40 ArP6 Ar ratios up to 367.5, which are slightly enhanced compared to air (295.5). He accumulation ages, taken as the apparent residence time of the brines, were calculated to be 20 to 50 Ma. Compared to the other locations the formation water from Neustadt-Giewe contained enhanced hydrocarbon contents. The 813C1,2,3 values point to thermogenic hydrocarbons and to a marine source rock with a maturity corresponding to about 1.2 % vitrinite reflectivity. An origin from Corg-rich Zechstein sediments seems probable, organic material from significantly deeper-seated Carboniferous formations can be ruled out. The 8180 and ÖD values of the waters confirm that meteoric water played an important role in the brine genesis. The determined isotopic composition of the meteoric component deviates from recent precipitation and indicates a last contact with the atmosphere at a time when climate conditions were significantly warmer than today. Gases dissolved in thermal waters can significantly affect both the technological suitability of a brine and the operation of a geothermal heat plant (scaling, degassing, occurence of flammable gases). If Corg-rich sedimentary rocks occur, the probability of the occurence of flammable gases increases in waters from larger depths, which are more economic due to their higher temperature. The pressure needed to prevent degassing inside a plant and thus to rninirnize scaling and uncontrolled degassing was calculated for the example of the thermal water cycle at Neustadt-Giewe (brine with the highest gas content). About 2 bars are sufficient to prevent degassing; however, flow effects require increasing the pressure up to about 4 bars. The constant composition of both the dissolved solids and gases over a period of 2 to 3 years is a sign of a relatively large spatial uniformity of the aquifers. Therefore the continuous operation of the plants seems unlikely to be endangered by a change in the chernical composition of the brines. The results of this study have shown that during the hydrodynarnic reconnaissance as weil as during the operation of a geothermal heat plant, precise knowlegde of the gas concentration is of essential importance.

Description: Late Miocene to Quaternary volcanic rocks from the frontal arc to the back-arc region of the Central Volcanic Zone in the Andes show a wide range of δ11B values (+4 to −7 ‰) and boron concentrations (6 to 60 ppm). Positive δ11B values of samples from the volcanic front indicate involvement of a 11B-enriched slab component, most likely derived from altered oceanic crust, despite the thick Andean continental lithosphere, and rule out a pure crust-mantle origin for these lavas. The δ11B values and boron concentrations in the lavas decrease with increasing depth of the Wadati-Benioff Zone. This across-arc variation in δ11B values and decreasing B/Nb ratios from the arc to the back-arc samples are attributed to the combined effects of boron-isotope fractionation during progressive dehydration in the slab and a steady decrease in slab-fluid flux toward the back arc, coupled with a relatively constant degree of crustal contamination as indicated by similar Sr, Nd and Pb isotope ratios in all samples. Three-component mixing calculations for slab-derived fluid, the mantle wedge and the continental crust based on B, Sr and Nd isotope data indicate that the slab-fluid component dominates the boron composition of the fertile mantle and that the primary arc magmas were contaminated by an average addition of 15 to 30% crustal material. Modeling of fluid-mineral boron-isotope fractionation as a function of temperature shows that dehydration reactions liberate continuously changing fluid compositions from the slab during progressive subduction. A combination of a boron-isotope fractionation model and a temperature model for the Central Andean subduction zone fits the across-arc variation in δ11B and we conclude that the boron-isotope composition of arc volcanic rocks, especially in island arcs, is dominated by changing δ11B-composition of boron-rich slab-fluids during progressive dehydration. Owing to the decrease in slab-derived fluid flux crustal contamination becomes more important toward the back-arc. Because of the boron-isotope fractionation effect, across-arc variations in δ11B need not necessarily reflect different mixing proportions between boron derived from the slab-fluid and the mantle wedge.

Description: Seismological models of upper mantle structure provide important constraints on the Earth"s convection system. Resolving the details of the upper mantle discontinuities is important for modelling the composition of the mantle and for understanding the effect that the discontinuities may have on mantle convection. Recently, numerous permanent and temporary seismic stations and networks have been set up around the world. It is possible to get the seismic records for the research needs from data management systems like IRIS, GEOFON, GEOSCOPE, FREESIA, etc. The use of seismograms collected from a large number of stations and earthquakes around the world enable us to study the global and the regional structure of the Earth. In this work, the receiver function technique (e.g. Owens et. Al., 1995) is applied to study the upper mantle structure in the northwest Pacific subduction zone and in the Hawaiian hotspot area. In the northwest Pacific, the Pacific plate is subducted into the upper mantle to more than 600 km depth, indicated by seismicity. In Hawaii, the volcanic edifice of the Hawaiian Islands and seamounts are believed to result from the passage of the oceanic lithosphere over a stationary mantle hotspot (Wilson, 1963; Morgan, 1971; Morgan et. al., 1995). In both regions the upper mantle structure is affected by the cold and warm materials, respectively. To study the extension of the temperature anomaly is important for understanding the Earth"s convection system. The olivine component of the mantle material is intensively studied in laboratories (e.g. Ito and Takahashi, 1989; Irifune, 1987). With increasing temperature and pressure, the olivine crystal undergoes a series of phase transformations which will result in a variation of the seismic structure. The effect of the temperature anomaly on the main upper mantle discontinuities will be discussed in chapter 2. Recently, the receiver function technique is increasingly applied to investigate the upper mantle discontinuities. To isolate the upper mantle conversion phases, newly developed moveout correction and migration methods are applied to separately distributed seismic stations as well as station arrays. The receiver function method used in this study will be introduced in chapter 3. In chapter 4 and 5, receiver function studies in the area of the northwest Pacific subduction zone and the Hawaiian mantle plume are presented. Regional tectonic background and the previous seismological works in these two areas will be first introduced in each chapter, and followed by description of data, processing steps, results and interpretations. In chapter 6, I will summarize the observations of the 410 and 660 topography in the northwest Pacific subduction zone and in the area around the Hawaiian mantle plume.

Description: The volcanism responsible for creating the chain of the Hawaiian islands and seamounts is believed to mark the passage of the oceanic lithosphere over a mantle plume1,2. In this picture hot material rises from great depth within a fixed narrow conduit to the surface, penetrating the moving lithosphere3. Although a number of models describe possible plume–lithosphere interactions4, seismic imaging techniques have not had sufficient resolution to distinguish between them. Here we apply the S-wave ‘receiver function’ technique to data of three permanent seismic broadband stations on the Hawaiian islands, to map the thickness of the underlying lithosphere. We find that under Big Island the lithosphere is 100–110 km thick, as expected for an oceanic plate 90–100 million years old that is not modified by a plume. But the lithosphere thins gradually along the island chain to about 50–60 km below Kauai. The width of the thinning is about 300 km. In this zone, well within the larger-scale topographic swell, we infer that the rejuvenation model5 (where the plume thins the lithosphere) is operative; however, the largerscale topographic swell is probably supported dynamically.