ALBERT

Beschreibung: The Central Andes of southern Peru, Bolivia, Argentina and Chile (between 12°S and 42°S) comprise the largest orogenic plateau in the world associated with abundant arc volcanism, the Central Andean Plateau, as well as multiple segments of flat-slab subduction making this part of the Earth a unique place to study various aspects of active plate tectonics. The goal of this continental-scale ambient noise tomography study is to incorporate broad-band seismic data from 20 seismic networks deployed incrementally in the Central Andes from 1994 May to 2012 August, to image the vertically polarized shear wave velocity (Vsv) structure of the South American Cordillera. Using dispersion measurements calculated from the cross-correlation of 330 broad-band seismic stations, we construct Rayleigh wave phase velocity maps in the period range of 8–40 s and invert these for the shear wave velocity (Vsv) structure of the Andean crust. We provide a dispersion misfit map as well as uncertainty envelopes for our Vsv model and observe striking first-order correlations with our shallow results (∼5 km) and the morphotectonic provinces as well as subtler geological features indicating our results are robust. Our results reveal for the first time the full extent of the mid-crustal Andean low-velocity zone that we tentatively interpret as the signature of a very large volume Neogene batholith. This study demonstrates the efficacy of integrating seismic data from numerous regional broad-band seismic networks to approximate the high-resolution coverage previously only available though larger networks such as the EarthScope USArray Transportable Array in the United States.

Beschreibung: We present a new interface between the geochemical simulator PHREEQC and the open source language R. It represents a tool to flexibly and efficiently program and automate every aspect of geochemical modelling. The interface helps particularly to setup and run large numbers of simulations and visualise the results. Also profiting of numberless high-quality R extension packages, performing sensitivity analysis or Monte Carlo simulations becomes straightforward. Further, an algorithm to speedup reactive transport simulations starting from homogeneous or zone- homogeneous state is programmed and successfully evaluated through the interface. It proved effective and could therefore be included in any reactive transport simulator.

Beschreibung: We studied 40 artesian wells (AWs) in the Amu Darya Delta. These wells include high-salinity (∼ 52 g/l) and saline (5 – 24 g/l) waters but are mostly low-salinity waters (1.3 – 2.9 g/l). The low-salinity AWs cluster into three types, reflecting the variable mixing of different end-member solutes: (residual) brines and solutes deriving from silicate alteration, dissolution of limestone and dissolution of gypsum. The solutes are all undersaturated in calcite and gypsum, contain a substantial cation excess against dissolved inorganic carbon and are characterised by low Ca/SO4 ratios. On the basis of the hydrochemical mass budgets of model cases, we demonstrate that Na-rich Cl-brines (45-48%) and a Na2SO4-brine (30-47%) are the dominant solute components. The solutes derived from aluminium silicate alteration are minor components (7.3 – 19.4%). Even less important are solutes from limestone or gypsum dissolution (0.05 – 3.7%). These waters are unlikely to have originated from sediments hosting gypsum. The low-salinity AWs must have acquired their dominant hydrochemical signatures under non-equilibrium conditions between their remote (unknown) seepage areas and their discharge locations. This acquisition may have begun during the early hydrochemical groundwater evolution when meteoric or surface water passed the critical zone under an arid climate regime. Warmer saline AWs (∼40°C) hosted in deeper Cretaceous formations contain a high portion of NaCl-rich brine (85%) and some are saturated in gypsum. These waters were derived from fluids rising along faults from pre-Cretaceous strata. The high-salinity and relatively cold AWs discharge close to the retreating Aral Sea south of its western basin. These AWs are suboxic, and Si concentrations are very low. The AW hydrochemical signatures reflect the dissolution of halite and gypsum. We observed positive correlations between temperature, Br, B and Si. The temperature correlation with bromide likely documents the transformation of organically bound Br. The silica concentrations in low-salinity AWs southeast of the Aral Sea (eastern basin) are close to quartz saturation and define a chemical Si-geothermometer.

Beschreibung: We applied scaled physical analogue experiments to investigate the early development of salt diapirs induced by differential sedimentary loading in an intra-continental basin realm (e.g. the North German Basin). During the experiments, deformation in a salt-analogue viscous layer was initiated by variations in the thickness of an overlying brittle material and subsequent accumulation of the brittle material further sustained deformation. A 2D optical image correlation system was used to monitor the strain evolution in the salt analogue material. Our models indicate that the formation of salt pillow structures can be achieved by minimum variations in the overburden loading. The increase of differential loading by adding synkinematic layers in the subsided areas causes not only an active piercing of the viscous layer through the brittle overburden but also an additional uplift in the adjacent areas. These elevations, named “secondary structures”, act as origins for a successive generation of diapirs. Consequently, an initial perturbation of the salt–sediment-interface can lead to a lateral propagation temporally shifted diapirs. The linkage between primary and secondary structures is reflected in the synkinematic overburden layers such as overlapping peripheral sinks in the transition zone between two diapirs. These sinks, in turn, are a frequently observable phenomenon around salt structures of the North German basin indicating that “secondary diapirism” is an underestimated process – besides regional tectonic stresses – influencing the evolution of salt structures.

Beschreibung: On 2012 May 20 and 29, two damaging earthquakes with magnitudes Mw 6.1 and 5.9, respectively, struck the Emilia-Romagna region in the sedimentary Po Plain, Northern Italy, causing 26 fatalities, significant damage to historical buildings and substantial impact to the economy of the region. The earthquake sequence included four more aftershocks with Mw ≥ 5.0, all at shallow depths (about 7–9 km), with similar WNW–ESE striking reverse mechanism. The timeline of the sequence suggests significant static stress interaction between the largest events. We perform here a detailed source inversion, first adopting a point source approximation and considering pure double couple and full moment tensor source models. We compare different extended source inversion approaches for the two largest events, and find that the rupture occurred in both cases along a subhorizontal plane, dipping towards SSW. Directivity is well detected for the May 20 main shock, indicating that the rupture propagated unilaterally towards SE. Based on the focal mechanism solution, we further estimate the co-seismic static stress change induced by the May 20 event. By using the rate-and-state model and a Poissonian earthquake occurrence, we infer that the second largest event of May 29 was induced with a probability in the range 0.2–0.4. This suggests that the segment of fault was already prone to rupture. Finally, we estimate peak ground accelerations for the two main events as occurred separately or simultaneously. For the scenario involving hypothetical rupture areas of both main events, we estimate Mw = 6.3 and an increase of ground acceleration by 50 per cent. The approach we propose may help to quantify rapidly which regions are invested by a significant increase of the hazard, bearing the potential for large aftershocks or even a second main shock.

Beschreibung: This PhD project about the effect of water incorporation on the structure and phase stability of wadsleyite and ringwoodite is integrated in the DFG priority program 1236 "Strukturen und Eigenschaften von Kristallen bei extrem hohen Drücken und Temperaturen". The corresponding research work was conducted at the Helmholtz Centre Potsdam, German Research Centre for Geosciences, GFZ, Department 3.3 Chemistry and Physics of Earth Materials. Seismic profiles of the Earth’s inner structure reveal discontinuities in the p- and s-wave velocities at certain depths. The discontinuities at 410, 520, and 660 km depth are assigned to the transformations of the (Mg,Fe)2SiO4-polymorphs olivine (a-form) to wadsleyite (ß) and ringwoodite (?). However, the observed depths and widths of these velocity jumps are not constant but vary on a global scale, especially in the case of d520. The reason for that has been subject matter of various discussions. The main issue of this PhD work is to evaluate the effect of hydrogen on the structure and phase stabilities of wadsleyite and ringwoodite and to investigate if the incorporation of water in these minerals might be responsible for the observed depths variations of d520. The experimental approach included the performance of high-pressure syntheses (varied parameters: pressure, water content, composition, oxygen fugacity) in a multi-anvil apparatus and an extensive investigation of the synthesized material. X-ray diffraction techniques and electron microprobe analyses were applied to identify the samples and define their structure and composition in detail. However, the main focus of the work was to localize and quantify hydrogen (and iron (Fe)) within the samples by spectroscopic techniques and to evaluate the effect of the incorporated species on the structure and phase stabilities of wadsleyite and ringwoodite. In the first part of this study the pressure-depending behavior of dry vs. hydrous iron free wadsleyite was investigated by IR spectroscopy. Thereby we could show that the incorporation of hydrogen shifts the phase transition from orthorhombic to monoclinic wadsleyite about 1.6 GPa to lower pressures. In the second part, the location of hydrogen in ringwoodite was investigated. We found that the main mechanisms are related to octahedral vacancies [VMg(OH)2]x and the hydrogarnet substitution [VSi(OH)4]x. The third part of the work was related to the effect of non-hydrostatic pressure conditions on the structure of hydrous ringwoodite. Thereby we could show that such conditions lead to a stress-induced proton disorder. In the fourth part we investigated the direct effect of hydrogen, iron and different oxygen fugacities on the phase relations between wadsleyite and ringwoodite. Thus we could prove that the incorporation of hydrogen expands the stability field of wadsleyite towards higher pressure and that this effect is even enhanced at oxidizing compared to reducing conditions in the experiment. The last part of the work consisted of calorimetric measurements on dry wadsleyite. The collected data present the basis for future action on the thermodynamic modeling of dry and hydrous wadsleyite and ringwoodite. On basis of the results of this study, we could prove that there is an effect of water on the phase relations between wadsleyite and ringwoodite that possibly can explain the observed variations in the shape of the 520km-discontinuity., Die vorliegende Arbeit behandelt den Einfluss des Wassereinbaus auf die Struktur und Phasenstabilitäten von Wadsleyit und Ringwoodit und ist eingegliedert in das DFG Schwerpunktprogramm 1236 mit dem Titel “Strukturen und Eigenschaften von Kristallen bei extrem hohen Drücken und Temperaturen”. Die dazugehörigen Forschungsarbeiten wurden am Helmholtz-Zentrum Potsdam, Deutsches GeoForschungsZentrum, GFZ, Department 3.3 Chemie und Physik der Geomaterialien durchgeführt. Seismische Profile, die die Struktur des Erdinneren abbilden, weisen in bestimmten Erdtiefen Unstetigkeiten in den p- und s-Wellengeschwindigkeiten auf. Die Diskontinuitä en in 410, 520 und 660 km Tiefe werden den Phasenumwandlungen der (Mg,Fe)2SiO4-Polymorphe Olivin (a-Polymorph) zu Wadsleyit (ß) und Ringwoodit (?) zugeordnet. Jedoch treten diese Unstetigkeiten global gesehen nicht exakt in der gleichen Tiefe auf, sondern weisen mitunter große Schwankungen auf. Dafür werden verschiedenste Gründe angeführt. Die vorliegende Arbeit soll in diesem Zusammenhang den Einfluss von Wasserstoff auf die Struktur und Phasenstabilitäten von Wadsleyit und Ringwoodit untersuchen sowie klären, ob der Einbau von Wasser in diese Minerale als Erklärung für die beobachteten Tiefenschwankungen der 520km-Diskontinuität herangezogen werden kann. Die experimentelle Herangehensweise an das Thema beinhaltete die Durchführung von Hochdrucksynthesen (veränderliche Parameter: Druck, Wassergehalt, chemische Zusammensetzung, Sauerstofffugazität) in einer Multi-Anvil-Apparatur sowie die anschließende ausführliche Untersuchung des synthetisierten Materials. Röntgenbeugungsanalysen sowie Mikrosondenuntersuchungen wurden angewendet, um die Phasen zu identifizieren und deren Struktur und chemische Zusammensetzung im Detail zu bestimmen. Das Hauptaugenmerk dieser Arbeit lag jedoch darin, Wasserstoff (und Eisen (Fe)) in der Struktur mit Hilfe von spektroskopischen Methoden zu lokalisieren, zu quantifizieren und den Einfluss der eingebauten Spezies auf die Struktur und Phasenstabilitäten von Wadsleyit und Ringwoodit zu bewerten. Im ersten Teil der Studie wurde daher das druckabhängige Verhalten von trockenem gegenüber wasserhaltigem Mg-Wadsleyit mittels IR-Spektroskopie untersucht. Dabei konnten wir zeigen, dass der Einbau von Wasserstoff die Phasenumwandlung vom orthorhombischen in den monoklinen Wadsleyit um etwa 1.6 GPa zu geringeren Drücken verschiebt. Im zweiten Teil wurde die genaue Positionierung von Wasserstoff innerhalb der Ringwooditstruktur untersucht. Der Hauptmechanismus konnte dabei oktaedrischen Leerstellen zugeordnet werden ([VMg(OH)2]x), der zweite wichtige Einbaumechanismus wird über die Hydrogranat-Substitution ([VSi(OH)4]x) vollzogen. Der dritte Teil der Arbeit befasste sich mit dem Effekt von nicht hydrostatischen Druckbedingungen auf die Struktur von wasserhaltigem Ringwoodit. Dabei konnten wir zeigen, dass derartige Bedingungen zu einer stress-induzierten Unordnung des Wasserstoffes führen kann. Im vierten Teil der Arbeit untersuchten wir den direkten Einfluss von Wasserstoff, Eisen und unterschiedlichen Sauerstofffugazitäten auf die Phasenbeziehungen zwischen Wadsleyit und Ringwoodit. Auf diese Weise war es uns möglich, zu beweisen, dass der Einbau von Wasserstoff das Stabilitätsfeld von Wadsleyit zu höheren Drücken hin erweitert und dass darüberhinaus dieser Effekt noch verstärkt auftritt, wenn die Bedingungen im Experiment eher oxidierend als reduzierend sind. Im letzten Teil der Studie wurden kalorimetrische Messungen am trockenen Wadsleyit durchgeführt. Die daraus gewonnenen Daten stellen die Grundlage für weitere Studien zum thermodynamischen Modellieren der Eigenschaften von trockenem und wasserhaltigem Wadsleyit und Ringwoodit dar. Anhand unserer Untersuchungen konnten wir zeigen, dass es tatsächlich einen Einfluss von eingebautem Wasser auf die Phasenbeziehungen zwischen Wadsleyit und Ringwoodit gibt, welcher die beobachteten Schwankungen bezüglich der Tiefe und Breite der 520km-Diskontinuität erklären kann.

Beschreibung: We present regional-scale mass balances for 25 drainage basins of the Antarctic Ice Sheet (AIS) from satellite observations of the Gravity and Climate Experiment (GRACE) for the years 2002–2011. Satellite gravimetry estimates of the AIS mass balance are strongly influenced by mass movement in the Earth interior caused by ice advance and retreat during the last glacial cycle. Here, we develop an improved glacial-isostatic adjustment (GIA) estimate for Antarctica using newly available GPS uplift rates, allowing us to more accurately separate GIA-induced trends in the GRACE gravity fields from those caused by current imbalances of the AIS. Our revised GIA estimate is considerably lower than previous predictions, yielding an (upper) estimate of apparent mass change of 48 ± 18 Gt yr−1. Therefore, our AIS mass balance of −103 ± 23 Gt yr−1 is considerably less negative than previous GRACE estimates. The Northern Antarctic Peninsula and the Amundsen Sea Sector exhibit the largest mass loss (−25 ± 6 Gt yr−1 and −126 ± 11 Gt yr−1, respectively). In contrast, East Antarctica exhibits a slightly positive mass balance (19 ± 16 Gt yr−1), which is, however, mostly the consequence of compensating mass anomalies in Dronning Maud and Enderby Land (positive) and Wilkes and George V Land (negative) due to interannual accumulation variations. In total, 7% of the area constitute more than half of the AIS imbalance (53%), contributing −151 ± 9 Gt yr−1 to global mean sea-level change. Most of this imbalance is caused by long-term ice-dynamic speed up expected to prevail in the future.

Beschreibung: 3000 m of ice sheet thickness has ensured that central Greenland has kept it geothermal heat flow (GHF) distribution enigmatic. Some few direct ice temperature measurements from deep ice cores reveal a GHF of 50 to 60 mW/m2 in the Summit region and this is noticeably above what would be expected for the underlying Early Proterozoic lithosphere. In addition, indirect estimates from zones of rapid basal melting suggest extreme anomalies 15 to 30 times continental background. Subglacial topography indicates caldera like topographic features in the zones hinting at possible volcanic activity in the past [1], and all of these observations combined hint at an anomalous lithospheric structure. Further supporting this comes from new high-resolution P-wave tomography, which shows a strong thermal anomaly in the lithosphere crossing Greenland from east to west [2]. Rock outcrops at the eastern and western end of this zone indicate significant former magmatic activity, older in the east and younger in the west. Additionally, plate modelling studies suggest that the Greenland plate passed over the mantle plume that is currently under Iceland from late Cretaceous to Neogene times, consistent with the evidence from age of magmatism. Evidence of rapid basal melt revealed by ice penetrating radar along the hypocentre of the putative plume track indicates that it continues to affect the Greenland continental geotherm today. We analyse plume-induced thermal disturbance of the present-day lithosphere and their effects on the central Greenland ice sheet by using a novel evolutionary model of the climate-ice-lithosphere-upper mantle system. Our results indicate that mantle plume-induced erosion of the lithosphere has occurred, explaining caldera-type volcanic structures, the GHF anomaly, and requiring dyke intrusion into the crust during the early Cenozoic. The residual thermo-mechanical effect of the mantle plume has raised deep-sourced heat flow by over 25 mW/m2 since 60 Ma and explains the high basal melting rates of the Greenland ice sheet observed in the study area. [1] Fahnestock, M., Abdalati, W., Joughin, I., Brozena, J., Gogineni, P., 2001. High geothermal heat flow, Basal melt, and the origin of rapid ice flow in central Greenland. Science (New York, N.Y.). 294, 2338–2342. [2] Jakovlev, A.V., Bushenkova, N.A., Koulakov, I.Y., Dobretsov, N.L., 2012. Structure of the upper mantle in the Circum-Arctic region from regional seismic tomography. Russian Geology and Geophysics. 53, 963–971.

Beschreibung: We present in a statistical study a comparison of thermospheric mass density enhancements (ρrel) with electron temperature (Te), small-scale field-aligned currents (SSFACs), and vertical ion velocity (Vz) at high latitudes around noon magnetic local time (MLT). Satellite data from CHAMP (CHAllenging Minisatellite Payload) and DMSP (Defense Meteorological Satellite Program) sampling the Northern Hemisphere during the years 2002–2005 are used. In a first step we investigate the distribution of the measured quantities in a magnetic latitude (MLat) versus MLT frame. All considered variables exhibit prominent peak amplitudes in the cusp region. A superposed epoch analysis was performed to examine causal relationship between the quantities. The occurrence of a thermospheric relative mass density anomaly, ρrel 〉1.2, in the cusp region is defining an event. The location of the density peak is taken as a reference latitude (Δ MLat = 0°). Interestingly, all the considered quantities, SSFACs, Te, and Vz are co-located with the density anomaly. The amplitudes of the peaks exhibit different characters of seasonal variation. The average relative density enhancement of the more prominent density peaks considered in this study amounts to 1.33 during all seasons. As expected, SSFACs are largest in summer with average amplitudes equal to 2.56 μA m−2, decaying to 2.00 μA m−2 in winter. The event related enhancements of Te and Vz are both largest in winter (Δ Te =730 K, Vz =136 m s−1) and smallest in summer (Δ Te = 377 K, Vz = 57 m s−1. Based on the similarity of the seasonal behaviour we suggest a close relationship between these two quantities. A correlation analysis supports a linear relation with a high coefficient greater than or equal to 0.93, irrespective of season. Our preferred explanation is that dayside reconnection fuels Joule heating of the thermosphere causing air upwelling and at the same time heating of the electron gas that pulls up ions along affected flux tubes.

Beschreibung: Based on joint consideration of S receiver functions and surface-wave anisotropy we present evidence for the existence of a thick and layered lithosphere beneath the Kalahari Craton. Our results show that frozen-in anisotropy and compositional changes can generate sharp Mid-Lithospheric Discontinuities (MLD) at depths of 85 and 150–200 km, respectively. We found that a 50 km thick anisotropic layer, containing 3% S wave anisotropy and with a fast-velocity axis different from that in the layer beneath, can account for the first MLD at about 85 km depth. Significant correlation between the depths of an apparent boundary separating the depleted and metasomatised lithosphere, as inferred from chemical tomography, and those of our second MLD led us to characterize it as a compositional boundary, most likely due to the modification of the cratonic mantle lithosphere by magma infiltration. The deepening of this boundary from 150 to 200 km is spatially correlated with the surficial expression of the Thabazimbi-Murchison Lineament (TML), implying that the TML isolates the lithosphere of the Limpopo terrane from that of the ancient Kaapvaal terrane. The largest velocity contrast (3.6–4.7%) is observed at a boundary located at depths of 260–280 km beneath the Archean domains and the older Proterozoic belt. This boundary most likely represents the lithosphereasthenosphere boundary, which shallows to about 200 km beneath the younger Proterozoic belt. Thus, the Kalahari lithosphere may have survived multiple episodes of intense magmatism and collisional rifting during the billions of years of its history, which left their imprint in its internal layering.

Beschreibung: We document Quaternary fluvial incision driven by fault-controlled surface deformation in the inverted intermontane Gökırmak Basin in the Central Pontide mountains along the northern margin of the Central Anatolian Plateau. In-situ-produced 10Be, 21Ne, and 36Cl concentrations from gravel-covered fluvial terraces and pediment surfaces along the trunk stream of the basin (the Gökırmak River) yield model exposure ages ranging from 7 ± 1 ka to 346 ± 45 ka and average fluvial incision rates over the past ~350 ka of 0.28 ± 0.01 mm a-1. Similarities between river incision rates and coastal uplift rates at the Black Sea coast suggest that regional uplift is responsible for the river incision. Model exposure ages of deformed pediment surfaces along tributaries of the trunk stream range from 60 ± 5 ka to 110 ± 10 ka, demonstrating that the thrust faults responsible for pediment deformation were active after those times and were likely active earlier as well as explaining the topographic relief of the region. Together, our data demonstrate cumulative incision that is linked to active internal shortening and uplift of ~0.3 mm a-1 in the Central Pontide orogenic wedge, which may ultimately contribute to the lateral growth of the northern Anatolian Plateau.

Beschreibung: The Mackenzie and eastern Selwyn Mountains, Northwest Territories, Canada, are the northeast expression of the Cordilleran orogen and have a geologic history that spans the last one billion years. The region has undergone a diverse tectonic evolution, which is reflected in an equally diverse collection of mineral deposits and prospects. More than 300 of these deposits and prospects have been documented in this area of the Northwest Territories and here they are categorized into mineral deposit types and their mode of formation evaluated and highlighted. Stratiform/stratabound Cu-Ag occurrences are hosted in the Neoproterozoic Coates Lake Group, generally preserved in the hanging wall of the Cretaceous Plateau fault, and define a belt through the central part of the Mackenzie Mountains. Low-grade phosphatic stratiform iron (47.5% Fe) occurs as iron formation in the Neoproterozoic Rapitan Group in the very northwest of the Mackenzie Mountains. Sedimentary exhalative Zn-Pb (+/- Ba) deposits are preserved in Cambrian through Devonian strata of the Selwyn Basin in the eastern Selwyn Mountains. Numerous carbonate-hosted Zn-Pb (+/- base-metals) occurrences are located in the Paleozoic strata of the Mackenzie Platform in the Mackenzie Mountains. Cretaceous felsic-intermediate plutons, which occur throughout the eastern Selwyn Mountains, are associated with tungsten skarn (proximal to intrusions), base-metal skarn (distal from intrusions), rare metals, semi-precious tourmaline related to pegmatites, and vein-hosted emeralds. Other resources of potential interest include coal deposits, placer gold, and possible Carlin-type gold deposits that have recently been identified farther west in the Yukon.