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Flood design necessitates discharge estimates for large recurrence intervals. However, in a flood frequency analysis, the uncertainty of discharge estimates increases with higher recurrence intervals, particularly due to the small number of available flood data. Furthermore, traditional distribution functions increase unlimitedly without consideration of an upper bound discharge. Hence, additional information needs to be considered which is representative for high recurrence intervals. Envelope curves which bound the maximum observed discharges of a region are an adequate regionalisation method to provide additional spatial information for the upper tail of a distribution function. Probabilistic regional envelope curves (PRECs) are an extension of the traditional empirical envelope curve approach, in which a recurrence interval is estimated for a regional envelope curve (REC). The REC is constructed for a homogeneous pooling group of sites. The estimation of this recurrence interval is based on the effective sample years of data considering the intersite dependence among all sites of the pooling group. The core idea of this thesis was an improvement of discharge estimates for high recurrence intervals by integrating empirical and probabilistic regional envelope curves into the flood frequency analysis. Therefore, the method of probabilistic regional envelope curves was investigated in detail. Several pooling groups were derived by modifying candidate sets of catchment descriptors and settings of two different pooling methods. These were used to construct PRECs. A sensitivity analysis shows the variability of discharges and the recurrence intervals for a given site due to the different assumptions. The unit flood of record which governs the intercept of PREC was determined as the most influential aspect. By separating the catchments into nested and unnested pairs, the calculation algorithm for the effective sample years of data was refined. In this way, the estimation of the recurrence intervals was improved, and therefore the use of different parameter sets for nested and unnested pairs of catchments is recommended. In the second part of this thesis, PRECs were introduced into a distribution function. Whereas in the traditional approach only discharge values are used, PRECs provide a discharge and its corresponding recurrence interval. Hence, a novel approach was developed, which allows a combination of the PREC results with the traditional systematic flood series while taking the PREC recurrence interval into consideration. An adequate mixed bounded distribution function was presented, which in addition to the PREC results also uses an upper bound discharge derived by an empirical envelope curve. By doing so, two types of additional information which are representative for the upper tail of a distribution function were included in the flood frequency analysis. The integration of both types of additional information leads to an improved discharge estimation for recurrence intervals between 100 and 1000 years.
Large-scale volcanic deformation recently detected by radar interferometry (InSAR) provides new information and thus new scientific challenges for understanding volcano-tectonic activity and magmatic systems. The destabilization of such a system at depth noticeably affects the surrounding environment through magma injection, ground displacement and volcanic eruptions. To determine the spatiotemporal evolution of the Lazufre volcanic area located in the central Andes, we combined short-term ground displacement acquired by InSAR with long-term geological observations. Ground displacement was first detected using InSAR in 1997. By 2008, this displacement affected 1800 km2 of the surface, an area comparable in size to the deformation observed at caldera systems. The original displacement was followed in 2000 by a second, small-scale, neighbouring deformation located on the Lastarria volcano. We performed a detailed analysis of the volcanic structures at Lazufre and found relationships with the volcano deformations observed with InSAR. We infer that these observations are both likely to be the surface expression of a long-lived magmatic system evolving at depth. It is not yet clear whether Lazufre may trigger larger unrest or volcanic eruptions; however, the second deformation detected at Lastarria and the clear increase of the large-scale deformation rate make this an area of particular interest for closer continuous monitoring.
Das Parallel-Seismik-Verfahren dient vor allem der nachträglichen Längenmessung von Fundamentpfählen oder ähnlichen Elementen zur Gründung von Bauwerken. Eine solche Messung wird beispielsweise notwendig, wenn ein Gebäude verstärkt, erhöht oder anders als bisher genutzt werden soll, aber keine Unterlagen mehr über die Fundamente vorhanden sind. Das Messprinzip des schon seit einigen Jahrzehnten bekannten Verfahrens ist relativ einfach: Auf dem Pfahlkopf wird meist durch Hammerschlag eine Stoßwelle erzeugt, die durch den Pfahl nach unten läuft. Dabei wird Energie in den Boden abgegeben. Die abgestrahlten Wellen werden von Sensoren in einem parallel zum Pfahl hergestellten Bohrloch registriert. Aus den Laufzeiten lassen sich die materialspezifischen Wellengeschwindigkeiten im Pfahl und im Boden sowie die Pfahllänge ermitteln. Bisher wurde meist ein sehr einfaches Verfahren zur Datenauswertung verwendet, das die Länge der Pfähle systematisch überschätzt. In der vorliegenden Dissertation wurden die mathematisch-physikalischen Grundlagen beleuchtet und durch Computersimulation die Wellenausbreitung in Pfahl und Boden genau untersucht. Weitere Simulationen klärten den Einfluss verschiedener Mess- und Strukturparameter, beispielsweise den Einfluss von Bodenschichtung oder Fehlstellen im Pfahl. So konnte geklärt werden, in welchen Fällen mit dem Parallel-Seismik-Verfahren gute Ergebnisse erzielt werden können (z. B. bei Fundamenten in Sand oder Ton) und wo es an seine Grenzen stößt (z. B. bei Gründung im Fels). Auf Basis dieser Ergebnisse entstand ein neuer mathematischer Formalismus zur Auswertung der Laufzeiten. In Verbindung mit einem Verfahren zur Dateninversion, d. h. der automatischen Anpassung der Unbekannten in den Gleichungen an die Messergebnisse, lassen sich sehr viel genauere Werte für die Pfahllänge ermitteln als mit allen bisher publizierten Verfahren. Zudem kann man nun auch mit relativ großen Abständen zwischen Bohrloch und Pfahl (2 - 3 m) arbeiten. Die Methode wurde an simulierten Daten ausführlich getestet. Die Messmethode und das neue Auswerteverfahren wurden in einer Reihe praktischer Anwendungen getestet – und dies fast immer erfolgreich. Nur in einem Fall komplizierter Fundamentgeometrie bei gleichzeitig sehr hoher Anforderung an die Genauigkeit war schon nach Simulationen klar, dass hier ein Einsatz nicht sinnvoll ist. Dafür zeigte es sich, dass auch die Länge von Pfahlwänden und Spundwänden ermittelt werden kann. Die Parallel-Seismik-Methode funktioniert als einziges verfügbares Verfahren zur Fundamentlängenermittlung zugleich in den meisten Bodenarten sowie an metallischen und nichtmetallischen Fundamenten und kommt ohne Kalibrierung aus. Sie ist nun sehr viel breiter einsetzbar und liefert sehr viel genauere Ergebnisse. Die Simulationen zeigten noch Potential für Erweiterungen, zum Beispiel durch den Einsatz spezieller Sensoren, die zusätzliche Wellentypen empfangen und unterscheiden können.
Temporal gravimeter observations, used in geodesy and geophysics to study variation of the Earth’s gravity field, are influenced by local water storage changes (WSC) and – from this perspective – add noise to the gravimeter signal records. At the same time, the part of the gravity signal caused by WSC may provide substantial information for hydrologists. Water storages are the fundamental state variable of hydrological systems, but comprehensive data on total WSC are practically inaccessible and their quantification is associated with a high level of uncertainty at the field scale. This study investigates the relationship between temporal gravity measurements and WSC in order to reduce the hydrological interfering signal from temporal gravity measurements and to explore the value of temporal gravity measurements for hydrology for the superconducting gravimeter (SG) of the Geodetic Observatory Wettzell, Germany. A 4D forward model with a spatially nested discretization domain was developed to simulate and calculate the local hydrological effect on the temporal gravity observations. An intensive measurement system was installed at the Geodetic Observatory Wettzell and WSC were measured in all relevant storage components, namely groundwater, saprolite, soil, top soil and snow storage. The monitoring system comprised also a suction-controlled, weighable, monolith-filled lysimeter, allowing an all time first comparison of a lysimeter and a gravimeter. Lysimeter data were used to estimate WSC at the field scale in combination with complementary observations and a hydrological 1D model. Total local WSC were derived, uncertainties were assessed and the hydrological gravity response was calculated from the WSC. A simple conceptual hydrological model was calibrated and evaluated against records of a superconducting gravimeter, soil moisture and groundwater time series. The model was evaluated by a split sample test and validated against independently estimated WSC from the lysimeter-based approach. A simulation of the hydrological gravity effect showed that WSC of one meter height along the topography caused a gravity response of 52 µGal, whereas, generally in geodesy, on flat terrain, the same water mass variation causes a gravity change of only 42 µGal (Bouguer approximation). The radius of influence of local water storage variations can be limited to 1000 m and 50 % to 80 % of the local hydro¬logical gravity signal is generated within a radius of 50 m around the gravimeter. At the Geodetic Observatory Wettzell, WSC in the snow pack, top soil, unsaturated saprolite and fractured aquifer are all important terms of the local water budget. With the exception of snow, all storage components have gravity responses of the same order of magnitude and are therefore relevant for gravity observations. The comparison of the total hydrological gravity response to the gravity residuals obtained from the SG, showed similarities in both short-term and seasonal dynamics. However, the results demonstrated the limitations of estimating total local WSC using hydrological point measurements. The results of the lysimeter-based approach showed that gravity residuals are caused to a larger extent by local WSC than previously estimated. A comparison of the results with other methods used in the past to correct temporal gravity observations for the local hydrological influence showed that the lysimeter measurements improved the independent estimation of WSC significantly and thus provided a better way of estimating the local hydrological gravity effect. In the context of hydrological noise reduction, at sites where temporal gravity observations are used for geophysical studies beyond local hydrology, the installation of a lysimeter in combination with complementary hydrological measurements is recommended. From the hydrological view point, using gravimeter data as a calibration constraint improved the model results in comparison to hydrological point measurements. Thanks to their capacity to integrate over different storage components and a larger area, gravimeters provide generalized information on total WSC at the field scale. Due to their integrative nature, gravity data must be interpreted with great care in hydrological studies. However, gravimeters can serve as a novel measurement instrument for hydrology and the application of gravimeters especially designed to study open research questions in hydrology is recommended.
With the increasing availability of observational data from different sources at a global level, joint analysis of these data is becoming especially attractive. For such an analysis – oftentimes with little prior knowledge about local and global interactions between the different observational variables at hand – an exploratory, data-driven analysis of the data may be of particular relevance. In the present work we used generalized additive models (GAM) in an exemplary study of spatio-temporal patterns in the tropospheric NO2-distribution derived from GOME satellite observations (1996 to 2001) at global scale. We focused on identifying correlations between NO2 and local wind fields, a quantity which is of particular interest in the analysis of spatio-temporal interactions. Formulating general functional, parametric relationships between the observed NO2 distribution and local wind fields, however, is difficult – if not impossible. So, rather than following a modelbased analysis testing the data for predefined hypotheses (assuming, for example, sinusoidal seasonal trends), we used a GAM with non-parametric model terms to learn this functional relationship between NO2 and wind directly from the data. The NO2 observations showed to be affected by winddominated processes over large areas. We estimated the extent of areas affected by specific NO2 emission sources, and were able to highlight likely atmospheric transport “pathways”. General temporal trends which were also part of our model – weekly, seasonal and linear changes – showed to be in good agreement with previous studies and alternative ways of analysing the time series. Overall, using a non-parametric model provided favorable means for a rapid inspection of this large spatio-temporal NO2 data set, with less bias than parametric approaches, and allowing to visualize dynamical processes of the NO2 distribution at a global scale.
In 1915, Alfred Wegener published his hypotheses of plate tectonics that revolutionised the world for geologists. Since then, many scientists have studied the evolution of continents and especially the geologic structure of orogens: the most visible consequence of tectonic processes. Although the morphology and landscape evolution of mountain belts can be observed due to surface processes, the driving force and dynamics at lithosphere scale are less well understood despite the fact that rocks from deeper levels of orogenic belts are in places exposed at the surface. In this thesis, such formerly deeply-buried (ultra-) high-pressure rocks, in particular eclogite facies series, have been studied in order to reveal details about the formation and exhumation conditions and rates and thus provide insights into the geodynamics of the most spectacular orogenic belt in the world: the Himalaya. The specific area investigated was the Kaghan Valley in Pakistan (NW Himalaya). Following closure of the Tethyan Ocean by ca. 55-50 Ma, the northward subduction of the leading edge of India beneath the Eurasian Plate and subsequent collision initiated a long-lived process of intracrustal thrusting that continues today. The continental crust of India – granitic basement, Paleozoic and Mesozoic cover series and Permo-Triassic dykes, sills and lavas – has been buried partly to mantle depths. Today, these rocks crop out as eclogites, amphibolites and gneisses within the Higher Himalayan Crystalline between low-grade metamorphosed rocks (600-640°C/ ca. 5 kbar) of the Lesser Himalaya and Tethyan sediments. Beside tectonically driven exhumation mechanisms the channel flow model, that describes a denudation focused ductile extrusion of low viscosity material developed in the middle to lower crust beneath the Tibetan Plateau, has been postulated. To get insights into the lithospheric and crustal processes that have initiated and driven the exhumation of this (ultra-) high-pressure rocks, mineralogical, petrological and isotope-geochemical investigations have been performed. They provide insights into 1) the depths and temperatures to which these rocks were buried, 2) the pressures and temperatures the rocks have experienced during their exhumation, 3) the timing of these processes 4) and the velocity with which these rocks have been brought back to the surface. In detail, through microscopical studies, the identification of key minerals, microprobe analyses, standard geothermobarometry and modelling using an effective bulk rock composition it has been shown that published exhumation paths are incomplete. In particular, the eclogites of the northern Kaghan Valley were buried to depths of 140-100 km (36-30 kbar) at 790-640°C. Subsequently, cooling during decompression (exhumation) towards 40-35 km (17-10 kbar) and 630-580°C has been superseded by a phase of reheating to about 720-650°C at roughly the same depth before final exhumation has taken place. In the southern-most part of the study area, amphibolite facies assemblages with formation conditions similar to the deduced reheating phase indicate a juxtaposition of both areas after the eclogite facies stage and thus a stacking of Indian Plate units. Radiometric dating of zircon, titanite and rutile by U-Pb and amphibole and micas by Ar-Ar reveal peak pressure conditions at 47-48 Ma. With a maximum exhumation rate of 14 cm/a these rocks reached the crust-mantle boundary at 40-35 km within 1 Ma. Subsequent exhumation (46-41 Ma, 40-35 km) decelerated to ca. 1 mm/a at the base of the continental crust but rose again to about 2 mm/a in the period of 41-31 Ma, equivalent to 35-20 km. Apatite fission track (AFT) and (U-Th)/He ages from eclogites, amphibolites, micaschists and gneisses yielded moderate Oligocene to Miocene cooling rates of about 10°C/Ma in the high altitude northern parts of the Kaghan Valley using the mineral-pair method. AFT ages are of 24.5±3.8 to 15.6±2.1 Ma whereas apatite (U-Th)/He analyses yielded ages between 21.0±0.6 and 5.3±0.2 Ma. The southern-most part of the Valley is dominated by younger late Miocene to Pliocene apatite fission track ages of 7.6±2.1 and 4.0±0.5 Ma that support earlier tectonically and petrologically findings of a juxtaposition and stack of Indian Plate units. As this nappe is tectonically lowermost, a later distinct exhumation and uplift driven by thrusting along the Main Boundary Thrust is inferred. A multi-stage exhumation path is evident from petrological, isotope-geochemical and low temperature thermochronology investigations. Buoyancy driven exhumation caused an initial rapid exhumation: exhumation as fast as recent normal plate movements (ca. 10 cm/a). As the exhuming units reached the crust-mantle boundary the process slowed down due to changes in buoyancy. Most likely, this exhumation pause has initiated the reheating event that is petrologically evident (e.g. glaucophane rimmed by hornblende, ilmenite overgrowth of rutile). Late stage processes involved widespread thrusting and folding with accompanied regional greenschist facies metamorphism, whereby contemporaneous thrusting on the Batal Thrust (seen by some authors equivalent to the MCT) and back sliding of the Kohistan Arc along the inverse reactivated Main Mantle Thrust caused final exposure of these rocks. Similar circumstances have been seen at Tso Morari, Ladakh, India, 200 km further east where comparable rock assemblages occur. In conclusion, as exhumation was already done well before the initiation of the monsoonal system, climate dependent effects (erosion) appear negligible in comparison to far-field tectonic effects.
The Tibetan Plateau is the largest elevated landmass in the world and profoundly influences atmospheric circulation patterns such as the Asian monsoon system. Therefore this area has been increasingly in focus of palaeoenvironmental studies. This thesis evaluates the applicability of organic biomarkers for palaeolimnological purposes on the Tibetan Plateau with a focus on aquatic macrophyte-derived biomarkers. Submerged aquatic macrophytes have to be considered to significantly influence the sediment organic matter due to their high abundance in many Tibetan lakes. They can show highly 13C-enriched biomass because of their carbon metabolism and it is therefore crucial for the interpretation of δ13C values in sediment cores to understand to which extent aquatic macrophytes contribute to the isotopic signal of the sediments in Tibetan lakes and in which way variations can be explained in a palaeolimnological context. Additionally, the high abundance of macrophytes makes them interesting as potential recorders of lake water δD. Hydrogen isotope analysis of biomarkers is a rapidly evolving field to reconstruct past hydrological conditions and therefore of special relevance on the Tibetan Plateau due to the direct linkage between variations of monsoon intensity and changes in regional precipitation / evaporation balances. A set of surface sediment and aquatic macrophyte samples from the central and eastern Tibetan Plateau was analysed for composition as well as carbon and hydrogen isotopes of n-alkanes. It was shown how variable δ13C values of bulk organic matter and leaf lipids can be in submerged macrophytes even of a single species and how strongly these parameters are affected by them in corresponding sediments. The estimated contribution of the macrophytes by means of a binary isotopic model was calculated to be up to 60% (mean: 40%) to total organic carbon and up to 100% (mean: 66%) to mid-chain n-alkanes. Hydrogen isotopes of n-alkanes turned out to record δD of meteoric water of the summer precipitation. The apparent enrichment factor between water and n-alkanes was in range of previously reported ones (≈-130‰) at the most humid sites, but smaller (average: -86‰) at sites with a negative moisture budget. This indicates an influence of evaporation and evapotranspiration on δD of source water for aquatic and terrestrial plants. The offset between δD of mid- and long-chain n-alkanes was close to zero in most of the samples, suggesting that lake water as well as soil and leaf water are affected to a similar extent by those effects. To apply biomarkers in a palaeolimnological context, the aliphatic biomarker fraction of a sediment core from Lake Koucha (34.0° N; 97.2° E; eastern Tibetan Plateau) was analysed for concentrations, δ13C and δD values of compounds. Before ca. 8 cal ka BP, the lake was dominated by aquatic macrophyte-derived mid-chain n-alkanes, while after 6 cal ka BP high concentrations of a C20 highly branched isoprenoid compound indicate a predominance of phytoplankton. Those two principally different states of the lake were linked by a transition period with high abundances of microbial biomarkers. δ13C values were relatively constant for long-chain n-alkanes, while mid-chain n-alkanes showed variations between -23.5 to -12.6‰. Highest values were observed for the assumed period of maximum macrophyte growth during the late glacial and for the phytoplankton maximum during the middle and late Holocene. Therefore, the enriched values were interpreted to be caused by carbon limitation which in turn was induced by high macrophyte and primary productivity, respectively. Hydrogen isotope signatures of mid-chain n-alkanes have been shown to be able to track a previously deduced episode of reduced moisture availability between ca. 10 and 7 cal ka BP, indicated by a 20‰ shift towards higher δD values. Indications for cooler episodes at 6.0, 3.1 and 1.8 cal ka BP were gained from drops of biomarker concentrations, especially microbial-derived hopanoids, and from coincidental shifts towards lower δ13C values. Those episodes correspond well with cool events reported from other locations on the Tibetan Plateau as well as in the Northern Hemisphere. To conclude, the study of recent sediments and plants improved the understanding of factors affecting the composition and isotopic signatures of aliphatic biomarkers in sediments. Concentrations and isotopic signatures of the biomarkers in Lake Koucha could be interpreted in a palaeolimnological context and contribute to the knowledge about the history of the lake. Aquatic macrophyte-derived mid-chain n-alkanes were especially useful, due to their high abundance in many Tibetan Lakes and their ability to record major changes of lake productivity and palaeo-hydrological conditions. Therefore, they have the potential to contribute to a fuller understanding of past climate variability in this key region for atmospheric circulation systems.
The origin and evolution of granites has been widely studied because granitoid rocks constitute a major portion of the Earth ́s crust. The formation of granitic magma is, besides temperature mainly triggered by the water content of these rocks. The presence of water in magmas plays an important role due to the ability of aqueous fluids to change the chemical composition of the magma. The exsolution of aqueous fluids from melts is closely linked to a fractionation of elements between the two phases. Then, aqueous fluids migrate to shallower parts of the Earth ́s crust because of it ́s lower density compared to that of melts and adjacent rocks. This process separates fluids and melts, and furthermore, during the ascent, aqueous fluids can react with the adjacent rocks and alter their chemical signature. This is particularly impor- tant during the formation of magmatic-hydrothermal ore deposits or in the late stages of the evolution of magmatic complexes. For a deeper insight to these processes, it is essential to improve our knowledge on element behavior in such systems. In particular, trace elements are used for these studies and petrogenetic interpretations because, unlike major elements, they are not essential for the stability of the phases involved and often reflect magmatic processes with less ambiguity. However, for the majority of important trace elements, the dependence of the geochemical behavior on temperature, pressure, and in particular on the composition of the system are only incompletely or not at all experimentally studied. Former studies often fo- cus on the determination of fluid−melt partition coefficients (Df/m=cfluid/cmelt) of economically interesting elements, e.g., Mo, Sn, Cu, and there are some partitioning data available for ele- ments that are also commonly used for petrological interpretations. At present, no systematic experimental data on trace element behavior in fluid−melt systems as function of pressure, temperature, and chemical composition are available. Additionally, almost all existing data are based on the analysis of quenched phases. This results in substantial uncertainties, particularly for the quenched aqueous fluid because trace element concentrations may change upon cooling. The objective of this PhD thesis consisted in the study of fluid−melt partition coefficients between aqueous solutions and granitic melts for different trace elements (Rb, Sr, Ba, La, Y, and Yb) as a function of temperature, pressure, salinity of the fluid, composition of the melt, and experimental and analytical approach. The latter included the refinement of an existing method to measure trace element concentrations in fluids equilibrated with silicate melts di- rectly at elevated pressures and temperatures using a hydrothermal diamond-anvil cell and synchrotron radiation X-ray fluorescence microanalysis. The application of this in-situ method enables to avoid the main source of error in data from quench experiments, i.e., trace element concentration in the fluid. A comparison of the in-situ results to data of conventional quench experiments allows a critical evaluation of quench data from this study and literature data. In detail, starting materials consisted of a suite of trace element doped haplogranitic glasses with ASI varying between 0.8 and 1.4 and H2O or a chloridic solution with m NaCl/KCl=1 and different salinities (1.16 to 3.56 m (NaCl+KCl)). Experiments were performed at 750 to 950◦C and 0.2 or 0.5 GPa using conventional quench devices (externally and internally heated pressure vessels) with different quench rates, and at 750◦C and 0.2 to 1.4 GPa with in-situ analysis of the trace element concentration in the fluids. The fluid−melt partitioning data of all studied trace elements show 1. a preference for the melt (Df/m < 1) at all studied conditions, 2. one to two orders of magnitude higher Df/m using chloridic solutions compared to experiments with H2O, 3. a clear dependence on the melt composition for fluid−melt partitioning of Sr, Ba, La, Y, and Yb in experiments using chloridic solutions, 4. quench rate−related differences of fluid−melt partition coefficients of Rb and Sr, and 5. distinctly higher fluid−melt partitioning data obtained from in-situ experiments than from comparable quench runs, particularly in the case of H2O as starting solution. The data point to a preference of all studied trace elements for the melt even at fairly high salinities, which contrasts with other experimental studies, but is supported by data from studies of natural co-genetically trapped fluid and melt inclusions. The in-situ measurements of trace element concentrations in the fluid verify that aqueous fluids will change their composition upon cooling, which is in particular important for Cl free systems. The distinct differences of the in-situ results to quench data of this study as well as to data from the literature signify the im- portance of a careful fluid sampling and analysis. Therefore, the direct measurement of trace element contents in fluids equilibrated with silicate melts at elevated PT conditions represents an important development to obtain more reliable fluid−melt partition coefficients. For further improvement, both the aqueous fluid and the silicate melt need to be analyzed in-situ because partitioning data that are based on the direct measurement of the trace element content in the fluid and analysis of a quenched melt are still not completely free of quench effects. At present, all available data on element complexation in aqueous fluids in equilibrium with silicate melts at high PT are indirectly derived from partitioning data, which involves in these experiments assumptions on the species present in the fluid. However, the activities of chemical components in these partitioning experiments are not well constrained, which is required for the definition of exchange equilibria between melt and fluid species. For example, the melt-dependent variation of partition coefficient observed for Sr imply that this element can not only be complexed by Cl− as suggested previously. The data indicate a more complicated complexation of Sr in the aqueous fluid. To verify this hypothesis, the in-situ setup was also used to determine strontium complexation in fluids equilibrated with silicate melts at desired PT conditions by the application of X-ray absorption near edge structure (XANES) spectroscopy. First results show a strong effect of both fluid and melt composition on the resulting XANES spectra, which indicates different complexation environments for Sr.
Foreland-basin systems are excellent archives to decipher the feedbacks between surface and tectonic processes in orogens. The sedimentary architecture of a foreland-basin system reflects the balance between tectonic subsidence causing long-term accommodation space and sediment influx corresponding to efficiency of erosion and mass-redistribution processes. In order to explore the effects of climatic and tectonic forcing in such a system, I investigated the Oligo-Miocene foreland-basin sediments of the southern Alborz mountains, an intracontinental orogen in northern Iran, related to the Arabia-Eurasia continental collision. This work includes absolute dating methods such as 40Ar/39Ar and zircon (U-Th)/He thermochronology, magnetostratigraphy, sedimentological analysis, sandstone and conglomerate provenance study, carbon and oxygen isotope analysis, and clay mineralogy study. Results show a systematic correlation between coarsening-upward cycles and sediment accumulation rates in the basin on 105 to 106yr time scales. During thrust loading phases, the coarse-grained fraction supplied by the uplifting range is stored in the proximal part of the basin (sedimentary facies retrogradation), while fine-grained sediments are deposited in distal sectors. Variations in sediment provenance during these phases of enhanced tectonic activity give evidence for erosional unroofing phases and/or drainage-reorganization events. In addition, enhanced tectonic activity promoted the growth of topography and associated orographic barrier effects, as demonstrated by sedimentologic indicators and the analysis of stable C and O isotopes from calcareous paleosols and lacustrine/palustrine samples. Extensive progradation of coarse-grained deposits occurs during phases of decreased subsidence, when the coarse-grained fraction supplied by the uplifting range cannot be completely stored in the proximal part of the basin. In this environment, a reduction in basin subsidence is associated with laterally stacked fluvial channel deposits, and is related to intra-foreland uplift, as documented by growth strata, tectonic tilting, and sediment reworking. Increase in sediment accumulation rate associated with progradation of vertically-stacked coarse-grained fluvial channels also occurs. Paleosol O-isotope data shows that this increase is related to wetter climatic phases, suggesting that surface processes are more efficient and exhumation rates increase, giving rise to a positive feedback. Furthermore, isotopic and sedimentologic data show that starting from 10-9 Ma, climate became less arid with an increase in seasonality of precipitation. Because important changes were also recorded in the Mediterranean Sea and Asia at that time, the evidence for climatic variability observed in the Alborz mountains most likely reflects changes in Northern Hemisphere atmospheric circulation patterns. This study has additional implications for the evolution of the Alborz mountains and the Arabia-Eurasia continental collision zone. At the orogenic scale, the locus of deformation did not move steadily southward, but stepped forward and backward since Oligocene time. In particular, from ~ 17.5 to 6.2 Ma the orogen grew by a combination of frontal accretion and wedge-internal deformation on time scales of ca. 0.7 to 2 m.y. Moreover, the provenance data suggest that prior to 10-9 Ma the shortening direction changed from NW-SE to NNE-SSW, in agreement with structural data. On the scale of the entire collision zone, the evolution of the studied basins and adjacent mountain ranges suggests a new geodynamic model for the evolution of the Arabia-Eurasia continental collision zone. Numerous sedimentary basins in the Alborz mountains and in other locations of the Arabia-Eurasia collision zone record a change from a tensional (transtensional) to a compressional (transpressional) tectonic setting by ~ 36 Ma. I interpret this to reflect the onset of subduction of the stretched Arabian continental lithosphere beneath central Iran, leading to moderate plate coupling and lower- and upper-plate deformation (soft continental collision). The increase in deformation rates in the southern Alborz mountains from ~ 17.5 Ma suggests that significant upper-plate deformation must have started by the early Miocene most likely in response to an increase in degree of plate coupling. I suggest that this was related to the subduction of thicker Arabian continental lithosphere and the consequent onset of hard continental collision. This model reconciles the apparent lag time of 15-20 m.y between the late Eocene to early Oligocene age for the initial Arabia-Eurasia continental collision and the onset of widespread deformation across the collision zone to the north in early to late Miocene time.
Orthopyroxenes of a high temperature protomylonite of the Ivrea Zone, Northern Italy show twin like polysynthetic lamellae parallel to {210} of the hypersthene host. The transformation is caused by plastic deformation under high metamorphic conditions which has resulted in dynamic recrystallization of pyroxene and plagioclase. The lamellae consist of clinohypersthene. The twin plane and the lamellar clino-orthoinversion of hypersthene due to natural deformation have not been described hitherto.