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Supplemental material, sj-pdf-1-hol-10.1177_09596836231157059 for Holocene deglaciation and glacier readvances on the Fildes Peninsula and King George Island (Isla 25 de Mayo), South Shetland Islands, NW Antarctic Peninsula by Pablo Heredia Barión, Stephen J Roberts, Cornelia Spiegel, Steven A Binnie, Lukas Wacker, Joanna Davies, Imogen Gabriel, Vivienne J Jones, Simon Blockley, Emma J Pearson, Louise Foster, Sarah J Davies, Thomas P Roland, Emma P Hocking, Michael J Bentley, Dominic A Hodgson, Chris L Hayward, Robert D McCulloch, Jorge A Strelin and Gerhard Kuhn in The Holocene

The mid-Cretaceous was one of the warmest intervals of the past 140 million years (Myr) driven by atmospheric CO2 levels around 1000 ppmv. In the near absence of proximal geological records from south of the Antarctic Circle, it remains disputed whether polar ice could exist under such environmental conditions. Here we present results from a unique sedimentary sequence recovered from the West Antarctic shelf. This by far southernmost Cretaceous record contains an intact ~3 m-long network of in-situ fossil roots. The roots are embedded in a mudstone matrix bearing diverse pollen and spores, indicative of a temperate lowland rainforest environment at a palaeolatitude of ~82°S during the Turonian–Santonian (93–83 Myr). A climate model simulation shows that the reconstructed temperate climate at this high latitude requires a combination of both atmospheric CO2 contents of 1120–1680 ppmv and a vegetated land surface without major Antarctic glaciation, highlighting the important cooling effect exerted by ice albedo in high-CO2 climate worlds.

New low-temperature thermochronological data from granitic basement of western Marie Byrd Land (MBL) provide insights into the still poorly constrained tectonic and topographic evolution of West Antarctica during and after continental breakup. Here, we present the first apatite (U-Th-Sm)/He data from the Devonian Ford Granodiorite and the mid-Cretaceous Byrd Coast Granite suites from the Ford Ranges and the Edward VII Peninsula. Thermal history modeling integrating apatite (U-Th-Sm)/He dates of 109���68 Ma with revised apatite fission track data in combination with geologic information indicates a thermal history with diachronous enhanced cooling at ~100���60 Ma and subsequent slow cooling until the present day. Enhanced cooling at ~100���70 Ma was related to activity of the West Antarctic rift system and to continental breakup, thereby exhuming most samples to shallow crustal levels. Localized cooling at ~75���60 Ma is interpreted as resulting from faulting in the eastern Ross Sea region. Slow cooling after ~70���60 Ma corresponds with formation of erosion surfaces in western MBL. Comparison of our results from western MBL with data from the literature indicates progressive formation of erosion surfaces from west to east along the MBL-Thurston Island crustal blocks. Late Cenozoic activity of the West Antarctic rift system and MBL dome uplift appear to have caused only minor exhumation of

The uplift of the Shillong Plateau, in northeast India between the Bengal floodplain and the Himalaya Mountains, has had a significant impact on regional precipitation patterns, strain partitioning, and the path of the Brahmaputra River. Today, the plateau receives the highest measured yearly rainfall in the world and is tectonically active, having hosted one of the strongest intra-plate earthquakes ever recorded. Despite the unique tectonic and climatic setting of this prominent landscape feature, its exhumation and surface uplift history are poorly constrained. We collected 14 detrital river sand and 3 bedrock samples from the southern margin of the Shillong Plateau to measure erosion rates using the terrestrial cosmogenic nuclide 10Be. The calculated bedrock erosion rates range from 2.0 to 5.6 m My−1, whereas catchment average erosion rates from detrital river sands range from 48 to 214 m My−1. These rates are surprisingly low in the context of steep, tectonically active slopes and extreme rainfall. Moreover, the highest among these rates, which occur on the low-relief plateau surface, appear to have been affected by anthropogenic land-use change. To determine the onset of surface uplift, we coupled the catchment averaged erosion rates with topographic analyses of the plateau's southern margin. We interpolated an inclined, pre-incision surface from minimally eroded remnants along the valley interfluves and calculated the eroded volume of the valleys carved beneath the surface. The missing volume was then divided by the volume flux derived from the erosion rates to obtain the onset of uplift. The results of this calculation, ranging from 3.0 to 5.0 Ma for individual valleys, are in agreement with several lines of stratigraphic evidence from the Brahmaputra and Bengal basin that constrain the onset of topographic uplift, specifically the onset of flexural loading and the transgression from deltaic to marine deposition. Ultimately, our data corroborate the hypothesis that surface uplift was decoupled from the onset of rapid exhumation, which occurred several millions of years earlier.

The Paleocene was a time of transition for the Arctic, with magmatic activity of the High Arctic Large Igneous Province (HALIP) giving way to magmatism of the North Atlantic Large Igneous Province in connection to plate tectonic changes in the Arctic and North Atlantic. In this study we investigate the Paleocene magmatic record and sediment pathways of the Basilika Formation exposed in the Central Tertiary Basin of Svalbard. By means of geochemistry, SmNd isotopic signatures, and zircon UPb geochronology we investigate the characteristics of several bentonite layers contained in the Basilika Formation, as well as the provenance of the intercalated clastic sediments. Our data show that the volcanic ash layers of the Basilika Formation, which were diagenetically altered to bentonites, originate from alkaline continental-rift magmatism such as the last, explosive stages of the HALIP in North Greenland and the Canadian Arctic. The volcanic ash layers were deposited on Svalbard in a flat shelf environment with dominant sediment supply from the east. Dating of detrital zircons suggests that the detritus was derived from Siberian sources, primarily from the Verkhoyansk Fold-and-Thrust Belt, which would require transport over similar to 3000 km across the Arctic.

The Weddell Sea sector is one of the main formation sites for Antarctic Bottom Water and an outlet for about one fifth of Antarctica’s continental ice volume. Over the last few decades, studies on glacialegeological records in this sector have provided conflicting reconstructions of changes in ice-sheet extent and ice-sheet thickness since the Last Glacial Maximum (LGM at ca 23e19 calibrated kiloyears before present, cal ka BP). Terrestrial geomorphological records and exposure ages obtained from rocks in the hinterland of the Weddell Sea, ice-sheet thickness constraints from ice cores and some radiocarbon dates on offshore sediments were interpreted to indicate no significant ice thickening and locally restricted grounding-line advance at the LGM. Other marine geological and geophysical studies concluded that subglacial bedforms mapped on theWeddell Sea continental shelf, subglacial deposits and sediments over-compacted by overriding ice recovered in cores, and the few available radiocarbon ages from marine sediments are consistent with major ice-sheet advance at the LGM. Reflecting the geological interpretations, different icesheet models have reconstructed conflicting LGM ice-sheet configurations for the Weddell Sea sector. Consequently, the estimated contributions of ice-sheet build-up in the Weddell Sea sector to the LGM sealevel low-stand of w130 m vary considerably. In this paper, we summarise and review the geological records of past ice-sheet margins and past icesheet elevations in the Weddell Sea sector. We compile marine and terrestrial chronological data constraining former ice-sheet size, thereby highlighting different levels of certainty, and present two alternative scenarios of the LGM ice-sheet configuration, including time-slice reconstructions for post- LGM grounding-line retreat. Moreover, we discuss consistencies and possible reasons for inconsistencies between the various reconstructions and propose objectives for future research. The aim of our study is to provide two alternative interpretations of glacialegeological datasets on Antarctic Ice- Sheet History for the Weddell Sea sector, which can be utilised to test and improve numerical icesheet models

For many years it has been known that near surface isotherms are influenced by the topography (Lees 1910). Recently, a number of studies were pursued to quantify the effect of topography on low temperature isotherms (e.g. Stüwe et al. 1994, Mancktelow & Grasemann 1997). The magnitude of perturbation depends on several parameters: exhumation rate, geothermal gradient, wavelength and amplitude of topography, and finally by the age of surface relief change (Braun 2002)., conference

Das globale Klima erwärmt sich. Die Wahrscheinlichkeit der Auslösung von Kippeffekten nimmt zu, während sich der globale Meeresspiegelanstieg beschleunigt. Ein wichtiger Faktor für den Anstieg des Meeresspiegels ist der Massenabfluss von Eis aus dem grönländischen und antarktischen Eisschild. Um die Vorhersage ihres künftigen Beitrags zu verbessern, ist es von entscheidender Bedeutung, zu untersuchen, wie Eis auf großen und kleinen Skalen fließt und sich verformt. In dieser Arbeit konzentriere ich mich auf die Mikrostruktur des Eises, d. h. die Größe und Ausrichtung der Eiskristalle (CPO), und ihre Wechselwirkung mit chemischen Spurenstoffen. Verunreinigungen sind ein Indikator für das Klima, aber es wird auch angenommen, dass sie mikrostrukturelle Prozesse wie Deformation und Kornwachstum beeinflussen. Ich konzentriere mich auf die Lokalisierung von Spurenstoffen in der Mikrostruktur und wie die Chemie diese Lokalisierung beeinflusst. Ich untersuche hauptsächlich Eis aus dem Eiskern des East Greenland Ice-core Project (EGRIP) aus dem Nordostgrönländischen Eisstrom (NEGIS). Durch die Kombination von mikrostrukturellen (Gewebeanalysator, Mikrostrukturkartierung, visueller Stratigraphie Line-Scan), Spurenstoff-Analyse (Raman-Spektroskopie, induktiv gekoppelte Plasma-Massenspektrometrie 2D-Bildgewinnung) und geophysikalischen Methoden (boden- und luftgestütztes Radar) in Verbindung mit numerischer Modellierung werden verschiedene räumliche Skalen überbrückt, um ein ganzheitlicheres Bild des Eises im NEGIS zu erhalten. Ich führe die erste systematische Analyse von Spurenstoffen in der Mikrostruktur entlang eines Eiskerns durch. Im EGRIP-Eiskern befinden sich feste Spurenstoffe vorzugsweise im Korninneren, während sich lösliche Spurenstoffe hauptsächlich an den Korngrenzen befinden. Meine Forschung zeigt außerdem, dass die Mikrostruktur bei der Verwendung von Spurenstoffen als Klimaproxy berücksichtigt werden sollte, da die räumliche Variabilität auf der (Sub-)Millimeterskala sehr groß ist. Die analysierte Mikrostruktur im EGRIP-Eiskern hilft außerdem bei der Rekonstruktion der ursprünglichen Ausrichtung des Eiskerns, liefert die Grundlagen für eine verbesserte Methode zur Bestimmung des horizontalen Gefüges mit einem co-polarisierten phasenempfindlichen Radar und liefert neue Erkenntnisse über NEGIS, wie z. B. die Bestimmung des Alters von Falten innerhalb des Eisstroms und seiner räumlichen Variabilität in Anisotropie und Härte.

The Davie Ridge is the central morphological element of the Mozambique Channel between East Africa and Madagascar. It extends along the Davie Fracture Zone, which played an important part in the break-up of Gondwana 180 million years ago, were a part of East Gondwana moved southward along the East African coast (West Gondwana). About 120 Million years ago, the southward movement stopped and Madagascar reached its present position relative to Africa. The exact position of Madagascar and the Davie Ridge within Gondwana and their movement are not fully understood. In the beginning of 2014, an expedition to the Mozambique channel was conducted in the scope of the PAGE-FOUR and MOCOM projects to examine the crustal structure and its impacts for reconstructions of the plate tectonics of Gondwana. This thesis presents the four seismic refraction profiles modelled across the Davie Ridge between 11.5° S and 16.5° S. The presented models determine the continent-ocean-boundary along the northern coastline of Mozambique and reveal a continental origin for the southern Davie Ridge. The northern Mozambican margin shows a complex and varying continent ocean transition, which hints towards an oblique opening mechanism. The high velocity lower crustal body of central Mozambique can be followed northwards up to 15.5° S. A plate reconstruction includes for the first time the continental sliver of the Davie Ridge.

Understanding the Holocene is particularly important for providing the context for recent ice sheet dynamics a i.e. understanding whether current ice sheet dynamics are unusual or part of Holocene natural variability (Bentley et al., 2014). Knowledge on the most recent millennia of Antarctic Ice Sheet history is vital for evaluating the response of the ice sheet to various forcing agents, such as sea-level rise, atmospheric and oceanographic temperature changes, and for constraining grounding-line retreat on Holocene to recent time scales (Bentley et al., 2014). The main objective of this thesis is to add new data to reconstruct the Holocene deglaciation history of King George Island, South Shetland Islands, northwest Antarctic Peninsula, by investigating morpho-sedimentary records of glacigenic and coastal landforms and associated sediments from the on-shore ice-free areas around Maxwell Bay (King George Island), namely Potter Peninsula and Fildes Peninsulas. In order to accomplish the thesis objectives, I used (i) cosmogenic exposure dating and radiocarbon dating for absolute chronological constraints; (ii) stratigraphy and sedimentology for relative chronological constraints and reconstruction of paleoenvironmental conditions; (iii) geomorphological mapping for spatial distribution of landsystems; (iv) and ground-penetrating radar (GPR) investigations for the study of internal sedimentary architecture of coastal landforms. Radiocarbon dating results yield new age constraints for the onset of deglaciation on Potter Peninsula, which occurred around at or before 7.8 ka cal BP instead of an earlier accepted age of 9.5 ka cal BP. I provide additional evidence for a short-lived glacier re-advance between 7.2 and 7.0 ka cal BP. This re-advance is likely linked to a glacier re-advance or still-stand documented on South Shetland Islands for that time period. Nevertheless, climatic conditions associated with this glacial re-advance remain unclear. In contrast, on Fildes Peninsula, exposure and radiocarbon dating indicate that glacial oscillations were minimal during the last 7 ka. I applied radiocarbon dating to remnants of mosses preserved in moraines. The moraines were formed close to the present glacier limit between 0.5 and 0.1 ka cal BP, during the last glacier re-advance in South Shetland Islands. This advance is linked to reductions in summer/annual insolation coupled with a shift to more intense Southern Hemisphere westerly winds in the Southern Ocean. Stronger, and possibly more poleward-shifted southern westerly winds produced more precipitation-laden storm fronts passing over the South Shetland Islands and thus, increased ice accumulation. The data also show that between 1.9 and 1.3 ka cal BP a climatic optimum was reached on Fildes and Potter Peninsula, which lasted until the last glacier readvance. GPR investigations and radiocarbon dating from a gravel spit system on Potter Peninsula document coastal progradation during the late phase of the last glacier re-advance, with a stable relative sea-level. Results also show an interruption of spit progradation that coincides with a proposed onset of accelerated isostatic rebound in reaction to glacier retreat subsequent to the last glacier re-advance. Spit growth resumed in the late 19th century after the rate of isostatic rebound decreased, and continues until today. The findings of this thesis support both, glacio-isostatic adjustment (GIA) models that show limited and those which show more pronounced ice-load changes on the South Shetland Islands during the late Holocene, suggesting that some GIA model parameters for the South Shetland Islands (e.g., lithospheric thickness, mantle viscosity) need to be better constrained. Furthermore, my findings have implications for regional paleoclimatic reconstructions and on ice sheet modeling for the Holocene of the northwest Antarctic Peninsula region.

The West Antarctic continent formed during most of the Palaeozoic and Mesozoic era by accretion of crustal blocks to form the palaeo-Pacific margin of Gondwana. In the mid Cretaceous, Gondwana break-up was associated with a major change from convergence to extension along the palaeo-Pacific margin, which opened the West Antarctic rift system (WARS) and the Southern Pacific Ocean by separating Zealandia from West Antarctica. Further disintegration of Gondwana led to the separation of West Antarctica from South America by opening of the Drake Passage and the development of the Scotia Sea. Thus, Gondwana break-up and ensuing tectonic movements brought geographic isolation to Antarctica and potentially favoured the onset of glaciation. Extensive ice-cover of West Antarctica is itself one of the main challenges when trying to better constrain the geodynamic evolution since Gondwana break-up that remains poorly understood. This study focussed on western Marie Byrd Land (MBL) and the Thurston Island area which both form parts of the conjugate continental margins of Zealandia. Further investigation was carried out in the area of the South Orkney Islands and Elephant Island group (southern Scotia Sea). To comprehensively reconstruct the thermo-tectonic evolution of the upper 2-5 km of the crust, the main methods utilised in this study were apatite fission track (AFT) and apatite (U-Th-Sm)/He (AHe) thermochronology. Thermal history modelling of both AFT and AHe data was also carried out. For a better understanding of the geodynamic history, selected samples were analysed by means of U-Pb zircon geochronology and hornblende thermobarometry. The oldest thermochronological record was obtained from Carboniferous to Early Cretaceous (meta)igneous rocks of the Thurston Island area. Their AFT ages of 145-92 Ma and AHe ages of 112-43 Ma were integrated in thermal models and show episodes of cooling and reheating since the Late Palaeozoic. These episodes refer to exhumation and back-arc basin development between the Permian and the Early Cretaceous along the active paleo-Pacific margin. They also record exhumation during Early to mid Cretaceous basin inversion associated with magmatism and crustal thickening. Extension-related exhumation from 95 to 70 Ma occurred in response to the rifting between Zealandia and West Antarctica and from 75 to 60 Ma to activity along the Bellingshausen-Antarctic Plate boundary. Final exhumation since the Late Eocene was most-likely caused by activity of the WARS. Western MBL samples were mostly taken from the mid Cretaceous Byrd Coast Granite suite. These samples yield AFT and AHe ages of 105-68 Ma and thermal models are compatible with rapid tectonic exhumation from 105 to 95 Ma during WARS-extension. This was followed by a phase of exhumation between 95 and 80 Ma in response to rifting and breakup between Zealandia and West Antarctic. The southern-most samples record exhumation from 80-60 Ma due to faulting in the Ross Sea region. Slow cooling during the Late Cretaceous-Early Cenozoic corresponds with the formation of the West Antarctic erosion surface and relative tectonic quiescence. Late Cenozoic WARS rifting, MBL-dome uplift, and onset of glaciation appears to have had little effect on erosion processes in western MBL. Pre-mid Cretaceous sedimentary and metamorphic samples of the South Orkney Islands yield AFT ages of 77-54 Ma and AHe ages of 61-5 Ma. These ages, interpreted with the help of thermal history models record Late Cretaceous-Early Cenozoic margin-wide uplift and erosion of high-standing topography. Relatively slow exhumation since the Late Eocene was associated with the opening of the Powell Basin. Metamorphic and igneous samples from the Elephant Island group reveal AFT and AHe ages of 30-23 Ma and 6-2 Ma. A diorite and a granodiorite samples yield U-Pb zircon ages of 28 and 10 Ma. The geo- and thermochronological ages and the identified cooling episodes probably refer to two periods of major plate reorganisations in the southern Scotia Sea. First, intrusion and exhumation during the Oligocene occurred probably in response to inception of the Shackleton Fracture Zone and the West Scotia Ridge. Second, rapid tectonic exhumation in the Late Miocene/Pliocene occurred due to cessation of two spreading ridges coupled with the opening of the Bransfield Strait.

Detrital thermochronology is commonly utilized in geological research to quantify the thermotectonic history of orogens by looking at their erosional products. As such, understanding how the erosional processes infl uence the age distribution is necessary. For instance, the calculation of apatite (U-Th-Sm)/He (AHe) ages requires a correction for He loss by alpha-ejection at grain margins. However, in detrital minerals, the He-depleted outer part of the grain may be mechanically and chemically abraded during sediment transport, leading to over-correction of AHe ages. Consequently, in the fi rst part of the thesis, the focus is directed on developing an appropriate sampling strategy to measure the effect of the abrasion on the apatite crystals. We took sand samples from the upper drainage of the Kali Gandaki River in central Nepal in order to find continuously abraded apatites. Samples of the igneous source rock (the Mustang granite) were also dated by AHe and apatite fission track (AFT), to pinpoint the age signal of the source rock. The resulting distribution of detrital AHe ages of sand samples is in good agreement with published geologic constraints and provide the first evidence on the long-term erosion and exhumation history of the Mustang-Thakkhola graben, where virtually no thermochronological constraint yet exists. Furthermore, we demonstrate that abrasion of the detrital apatite grains is a major consequence of river transport within the first kilometres of river transport. We find evidence that the best approach in detrital settings is to analyse a homogeneous grain population but, in this case, the degree of alpha-correction application has to be considered carefully to achieve the distribution of the AHe ages that best represent the underlying cooling patterns. Furthermore, detrital thermochronology is enhanced by applying multiple techniques: to better resolve the cooling history of the Mustang graben, the AHe dataset is integrated with detrital AFT ages. To robustly interpret the combined age distribution, these AHe and AFT ages are compared to synthetic age predicted by a numerical model. The model finds the best agreement between synthetic and real data, by varying a set of parameters that relate to tectonic events and comparing,. The main outcome of the study is the clear constrain of the onset of extension between 13 and 11 Ma. When this result is interpreted in the frame of other neighbouring extensional structures, the Thakkhola graben appears as part of a larger system that accommodates arc-parallel extension and thus share a common timing of onset. In a third and final step, detrital AHe ages are is related to erosion rates obtained with cosmogenic nuclide 10Be. We collected 14 detrital river sand and 3 bedrock samples fromthe southern margin of the Shillong Plateau to measure erosion rates using the terrestrial cosmogenic nuclide 10Be. Erosion rates derived from cosmogenic 10Be from the deeply incised southern valleys of the Shillong Plateau are surprisingly low (50 to 80 m M y-1 ) in a region that is steep, tectonically active, and receives 7 m of annual rainfall. From our measured catchment-averaged erosion rates and estimates of the incised sediment volumes, we quantify the temporal duration of incision in the incised portion of the landscape, which we in turn relate to the onset of surface uplift. The resulting estimates, ranging from 4.4 A /- 0.6 to 4.6 A /- 0.7 Ma, match well with a set of external constraints and available low-temperature thermochronology data, and thus appear to provide a robust estimate for the initiation of surface uplift. In summary, the findings of this thesis highlight that detrital apatite (U-Th-Sm)/He thermochronology, especially in combination with other methods, such Apatite Fission Tracks or Cosmogenic Nuclide dating, is an effective method to address specific problems in the field of geodynamics and tectonic geomorphology.

A consolidated knowledge of the formation and dispersal of the former supercontinents reveals important evidence for the eartha s climate and biosphere in the past and contribute to the prediction of their future evolution. Nowadays, a main objective is the investigation of the initial break-up of the continental assembly of Gondwana that serves as a constraint for its subsequent dispersal and the evolution of all oceans and seas in the southern hemisphere. Evidence of the early rifting stages are expected at the margins of Southeast Africa and East Antarctica, whereas the latter one is difficult to access, due to its remote position and ice coverage. To understand the driving forces and the chronology of the break-up and of the massive volcanism additional detailed knowledge of the crustal setting along the margins of Southeast Africa is required. Therefor, a new geophysical dataset was acquired with the RV Sonne in the northern Mozambique Basin at the beginning of year 2014. This comprises a deep seismic sounding profile across a so-far unknown structural high, the Beira High. Additional gravity and magnetic data were systematically recorded across the entire northern Mozambique Basin. Based on velocity, amplitude, density and magnetic modelling, a geological model of the continental margin of Central Mozambique was prepared. A new compilation of all available magnetic data in the Mozambique Basin reveals information about the age of the sea floor, which serves as constraint for the reconstruction of the initial Gondwana break-up. The study depicts a continental origin of up to 23 km thick and partly highly intruded crust at Beira High. In the adjacent coastal areas of the south-western part of Central Mozambique, 7 km thin crust is observed, which is covered by more than 11 km thick sediments and implies the continuation of the continent-ocean transition towards onshore Mozambique. This is in clear contrast to the narrow transition observed in the north-eastern part of the margin and reveals a clear asymmetric crustal setting as supposed for the conjugate margin in the Riiser-Larsen Sea in Antarctica and consequently suggests a complex break-up scenario. The presence of a pronounced high-velocity lower crustal body is interpreted as magmatic material, which underplates the crust and extends about 200 km from the Central Mozambican margin towards the Mozambique Basin and testifies for the massive volcanism during the break-up. The distribution of further volcanics along the entire margin clearly depicts the continuation of the north-eastern branch of the Karoo large igneous province and are mainly emplaced between 177-157 Ma. The magmatism in Southeast Africa seemed to be continuous throughout the initial break-up, which points to the presence of either a mantle plume or a thermal anomaly as source of the giant magmatism. An additional late stage of rift-volcanism mainly affected the margin of Dronning Maud Land and causes the difference in the magnetic signature of the conjugate margins. The tracing of continuous fractures throughout the Africa-Antarctica Corridor leads to the reconstruction of a tight Gondwana fit prior rifting, which reveals several geological links between the plates. A main structure of the East African-Antarctic Orogen extends from the Namama Shear Zone in Central Mozambique across the Orvin Shear Zone towards the Forster magnetic anomaly in Dronning Maud Land. During the initial Gondwana break-up at 182 Ma, Beira High started to separate from West Gondwana along this suture until it demerged as well from East Gondwana by a rift jump. The investigation of further partly unknown tectonic structures along the western and southern coast of Mozambique revealed a possible oceanic origin of the southern part of the Mozambique Coastal Plains, due to similarities of the magnetic signature to the oceanic crust south of Beira High as well as the tentative identification of magnetic spreading anomalies. The subsequent emplaced Mozambique Ridge moved southwards as part of a micro plate during an additional active spreading centre in the Northern Natal Valley. The resulting reconstruction of the initial Gondwana break-up in the Africa-Antarctica Corridor accounts for all present-day available geological, geophysical and geodynamic constraints and might serve as a basis for the investigation of the subsequent dispersal of Gondwana.

The Walvis Ridge is a more than 3000km long submarine ridge in the South Atlantic, which consists of single volcanoes and numerous smaller and larger ridges. It stretches from Namibia at the African continental margin to the volcanic island of Tristan da Cunha near the Mid-Atlantic Ridge. At some places this remarkable structure raises from the 5000 m deep sea basins to the sea surface or even above. The hypotheses about its origin are strongly related to the great debate about the existence of deep mantle plumes: The ridge is thought to be either the hotspot trail of the Tristan hotspot or the result of stress release caused by normal plate tectonics. The hotspot hypothesis further links the ridge to continental flood basalts, which are thought to be emplaced by an arriving plume. A temporal and spatial relation between the eruption of flood basalts and continental breakup gave rise to the idea that plumes are an important parameter for controlling continental breakups. In 2011 a large geophysical experiment was carried out at the landfall of Walvis Ridge in order to constrain its origin and the influence of the proposed plume head on the opening of the South Atlantic. Here, I present the crustal structure of the Walvis Ridge and the adjacent continental crust derived from two seismic refraction lines and gravity modelling. One line extends 480km across the ridge in approximately 600km distance to the coastline. The other profile covers the continental margin. It extends 430 km along the ridge axis and continues 290 km onshore. My results show that the Walvis Ridge consists of thickened oceanic crust with a thickness of 18-22 km. The crustal thickness decreases with increasing distance from the continental margin. Magmatic rocks cover a major fracture zone and pre-existing oceanic crust. Therefore, they must have been emplaced after the transform fault became inactive. Furthermore, the fracture zone is in about 100 km distance from the main ridge axis indicating that the ridge formed independent of the fracture zone. I conclude that normal stress release along a transform fault cannot account for the formation of the Walvis Ridge and support a hotspot origin. Abnormally high seismic velocities above 7.3km/s are observed in the lower crust at the continent-ocean transition. This high velocity lower crustal body (HVLCB) intrudes into the continental crust and terminates at the Kaoko fold belt. Similar HVLCB have been observed along the continental margin south of Walvis Ridge. The seaward termination of the HVLCB at Walvis Ridge is comparable to those. In contrast, the landward termination occurs 100 km further in land and is attributed to the presence of a mantle anomaly during the initial rift stage. Complementary seismic studies with a perpendicular line orientation show that this HVLCB is very limited in its width, even narrower than offshore. The influence of the hotspot was therefore very localized and the distribution of intrusive material resembles a narrow conduit rather than a broad plume head. I therefore question the presence of massive plume head during the the opening of the South Atlantic. From this it follows that the continental breakup has unlikely been initiated an arriving plume head.

The Weddell Sea basin is of particular significance for understanding climate processes, including the generation of ocean water masses and their influences on ocean circulation as well as the Antarctic ice sheets dynamics. The sedimentary record, preserved in the basin serves as an archive of the pre-glacial to glacial development, ocean circulation and tectonic evolution. This thesis focuses on understanding the sedimentation history and reconstructing paleo-water depths, using all available multichannel seismic lines and existing drilling sites, with the aim to apply the paleo-water depths to General Circulation Models (GCM) of the Weddell Sea basin. A series of sedimentary thicknesses grids (pre-glacial, transitional, full-glacial) and paleobathymetric grids produced in this work are essential contributions for numerical climate simulations and ocean circulations. These sedimentary thickness grids allow the comparison of sedimentary regimes of the pre-glacially dominated and glacially dominated stages of Weddell Sea history. The pre-glacial deposition with thicknesses of up to 5 km was controlled by the tectonic evolution and sea-floor spreading history interacting with terrigenous sediment supply. The transitional unit shows a relatively high sedimentation rate and has thicknesses of up to 3 km, which may be attributed to an early formation of the East Antarctic Ice Sheet having partly advanced to the coast or even inner shelf. The main deposition centre of the full-glacial unit lies in front of the Filchner-Ronne Ice Shelf and has sedimentation rates of up to 140-200 m/Myr, which infers that ice sheets grounded on the middle to outer shelf and that bottom-water currents strongly impacted the deep-sea sedimentation in the middle Miocene. The paleobathymetric grids at 15, 34 and 120 Ma are reconstructed by using a backstripping technique and applied to constrain paleoclimate models. Coupled GCM runs are forced by global warm climatic boundary conditions of the Mid-Miocene and the new Weddell Sea paleobathymetry data. The GCM model results suggest that deep water formation and ocean circulation are especially sensitive to the paleobathymetric configuration of the Weddell Sea which is mainly characterized by a more southerly shelf break than at present or in previous paleobathymetric reconstructions for the Miocene. The southwards shifted shelf break of the Weddell Sea results in dramatic changes in simulated mixed layer depth and bottom water formation. Intensification of this bottom water plays a significant role in sediment distribution and the geomorphology of the Weddell Sea margin, e.g. through the build-up of a number of large sediment drifts. In addition to the paleobathymetric study of the Weddell Sea, I carried out two seismic interpretation studies in the southeast Weddell Sea and along the Dronning Maud Land margin. Large deposition centers, the Crary Trough Mouth Fan and prominent sediment ridges, are interpreted as glacial deposits of the southeastern Weddell Sea. Two giant, sinuous, NE-SW-oriented sediment ridges are interpreted as turbidity-contourites, due to the complicated down-slope/along-slope processes occurring across their margins. The large catchment area, abundant sediment supply, fluctuating sea level and ice sheet dynamics are the major contributions for the sedimentation. The remarkable increase in mass-transport deposits during the Late Miocene and Middle to Late Pliocene is related to the build-up of pore overpressure during rapid sediment accumulation as well as changing sea level and may be triggered by glacio-isostatic paleoearthquakes. Based on seismic reflection data and well data acquired on the continental margin offshore Dronning Maud Land, the sedimentation processes are investigated. My investigations reveal that the Jutul-Penck Graben system on the Dronning Maud Land plays a significant role in erosion, transport, and deposition of sedimentary material. I further found seismic chimney structures in this region for the first time and attribute their formation to volcanic processes.

The aim of this thesis is the investigation of the Westantarcitc continental margin between Wrigely Gulf and the Amundsen Sea Embayment based on a geophysical dataset collected during two expedition of the research vessel Polarstern in 2006 and 2010. This study presents a compilation of 3D potential field forward modelling results inculding a set of seismic reflection and refraction profiles to investigate the lithospheric architecture and tectonic development of this poorly known part of Antarctica. The results presented in this study decipher the crustal structure and tectonic development in this area for the first time.

West Antarctica has gone through major tectonic changes beginning in the Cretaceous (145 - 66 Ma). With the West Antarctic Rift System, the area also holds one of the largest continental rifts known on Earth. However, the West Antarctic Rift System is almost completely buried beneath West Antarctic Ice Sheet, as a result details of its geodynamic history are sparse and its tectonic evolution is still poorly understood. Furthermore, with the 'Amundsen Sector', West Antarctica hosts one of the most rapidly changing parts of the West Antarctic Ice Sheet. With the fastest flowing ice streams in Antarctica, especially the eastern areas are characterized by rapid ice sheet thinning and grounding-line retreat. Like data on West Antarctica's geodynamics, constraints on the deglacial history are limited to either marine sedimentary data or a few isolated nunataks. Thus it is difficult to assess the long-term deglacial history of the area, too. In this study we reconstructed the shallow crustal (~15 - 1 km) evolution of the ~1000 km long Amundsen Sector of West Antarctica and alongside the rift system. Thereby we applied three lowtemperature thermochronology analysis: apatite (U-Th-Sm)/He, apatite fission track and zircon fission track, and combined their results in inverse thermal history models. We further utilized detrital information on the dominantly ice-covered hinterland through the analysis of ice rafted debris extracted from marine sediments. Finally, to address the glacial retreat after the Last Glacial Maximum (ca. 23 - 19 ka) we applied 10Be-surface exposure dating in two key areas onshore of the eastern and mid Amundsen Sector, namely Pine Island Bay and the Kohler Range. Together, all three thermochronology systems yield early Cretaceous to early Miocene ages (121 - 18 Ma), with a dominant cluster in the mid- to late Cretaceous. Zircon fission track data ranges between 108 - 80 Ma, apatite fission track between 121 - 28 Ma, with narrow track lengths distributions and mean track lengths of 14.9 - 13.1 um, apatite (U-Th-Sm)/He mean ages between 94 and 18 Ma. Dominant (subglacial) lithologies of the coastal Amundsen Sector are igneous rocks that presumable intruded into low-grade meta-sediments of early Paleozoic times, and from our data there is no indication for un-metamorphosed sedimentary bedrock beneath the ice. Thermal history modeling identifies two major cooling stages: beginning with a period of rapid cooling during the Cretaceous, which was replaced by a stage of relative tectonic stability and rather slow cooling in the Cenozoic. This phase of strong cooling is also present in the detrital data, indicating that the majority of the Amundsen Sector was strongly affected by the extension phase along the modern northern margin of the West Antarctic. The extension was part of the Gondwana break-up and ultimately lead to the separation of West Antarctica - New Zealand. Post-Cretaceous activity appears to be limited to block tilting along the Pine Island glacial trough and an isolated Miocene cooling signal within the mid Amundsen Sector, which is interpreted to reflect the exhumation of a fault-bound horst structure separated through fault zones that are resultant of or directly linked to activity in the West Antarctic Rift System. Apart from that our data implies a rather stable tectonic setting and shows no strong indication of significant glacial erosion for most of the Cenozoic. The 10Be surface-exposure ages indicate that the sampled nunataks in the Kohler Range are ice-free since about 13 and 9 ka, respectively. Exposure ages from Pine Island Bay range from 8 ka close to the Pine Island glacial trough to 9 ka from a more coastal island. This implies a general Holocene retreat and minimum long-term average thinning rates of ~3.3 cm/yr are one order of magnitude lower than recent rates based on satellite data. Our results thereby provide insights into the significance of local ice-sheet variations and suggest that the post-Last Glacial Maximum history in the Amundsen Sector was characterized by glacial thinning as well as lateral retreat in pre- to early Holocene times.

This PhD-thesis contains both, a classical low-temperature thermochronologic study from the European Central Alps (Lepontine Dome) and a new approach to couple apatite fission track analyses and numerical 'sandbox' modelling. Resulting, a refined kinematic evolution model for the Lepontine Dome is proposed. The newly developed approach to couple apatite fission track analyses and numerical sandbox modelling demonstrates the influence of deep crustal mechanic properties and geometries on upper crustal exhumation processes. Finally, the new approach is successfully applied to the Lepontine Dome.

In combining existing multichannel seismic reflection seismic data in the Weddell Sea deep-sea basin, with existing and newly acquired data in the Amundsen Sea and Ross Sea basins, previously unknown sequences representing the pre-glacial to glacial palaeoenvironmental development of the West Antarctic Margin were identified. Pre-glacial sediment deposition centres seemed to have changed near or after the Eocene/Oligocene boundary (~34 Ma) when the first major ice sheets advanced to and across the shelf. The middle Miocene (~16 Ma) full glacial sequences indicate a new depocentre formed North of the Amundsen Sea Embayment. Smaller depocentres in the Bellingshausen Sea and Antarctic Peninsula basins, shifted eastward. Calculations indicate ~4.6 km (~10.2 million km3) of West Antarctica's landmass were eroded since the Late Cretaceous and deposited in the Southern Pacific. This has implications for the palaeotopographic and palaeobathymetric reconstructions, and ice sheet climate models.

Extensive parts of the largely marine-based West Antarctic Ice Sheet are currently subject to the most rapid changes in the global cryosphere. In recent decades, ice streams that drain >35% from the ice sheet’s interior into the Amundsen Sea have been affected most dramatically. As upwelling, relatively warm Circumpolar Deep Water flows onto the continental shelf towards the deep inner shelf cavities, it melts the ice shelves from below, thins them, and causes ice stream acceleration and grounding line retreat in response to decreased buttressing. Since ice streams are marine-based on slopes that significantly deepen inland, they are susceptible to increased future ice mass loss, directly resulting in a sea-level rise of up to 3.4 meters, assuming that all marine-based West Antarctic ice portions would disintegrate and melt (Fretwell et al. 2013). However, ‘state-of-the-art’ ice sheet models that aim to elucidate these future scenarios are only initialised with observational data covering the past 30-40 years (e.g. Favier et al. 2014), thus excluding long-term empirical data of ice sheet change spanning the Last Glacial Maximum and the subsequent deglacial period. To test the reliability of predicted future scenarios it is essential that models are validated against past ice sheet configurations confirmed by empirical data from palaeo-ice sheet beds on modern Antarctic continental shelves. Attempts at reproducing the LGM ice sheet (Golledge et al. 2013), have revealed considerable mismatches between model simulations and empirical data. Such disparities have been attributed principally, to a lack of comprehensive palaeo-glaciological data particularly from outer continental shelves and regions in between the large palaeo-ice stream troughs, regions known as inter-ice stream ridges, that would reveal the spatial and temporal variations of the West Antarctic Ice Sheet in the Amundsen Sea sector of the Southern Ocean more precisely. This thesis presents the mapping and detailed analysis of new marine geophysical and geological data from three formerly unstudied regions on the Amundsen Sea shelf that significantly improve our understanding of Antarctic palaeo-ice sheet dynamics. In Chapter 2 I will present the first sea-floor geomorphological record of former basal ice conditions on an inter-ice stream ridge that entirely differ from those commonly investigated in the nearby palaeo-ice stream troughs. From these data, an improved temporal and spatial reconstruction of flow conditions of the former ice sheet in inter-ice stream areas of the eastern Amundsen Sea Embayment is revealed. Age constraints aiming to reveal the minimum grounding line retreat from the ridge broadly correspond with those from the nearby Pine Island Trough. Palaeo-ice sheet dynamics as inferred from the glacial landform and sediment record on the inter-ice stream ridge are well complemented by a large-scale multibeam bathymetry survey of the middle and outer shelf, north of the inter-ice stream area, presented in Chapter 3. This new dataset compiles bathymetry from 11 separate research cruises to the region, and is supplemented by the analysis of new sedimentological and seismic data. From comprehensive landform mapping, the detailed palaeo-flow pathways of the WAIS in the northern and easternmost Amundsen Sea Embayment is revealed. Furthermore, geomorphological analysis of the bathymetry data allows thermal regimes at the palaeo-ice sheet bed to be defined in unprecedented detail, showing the complex relation of trough geometries and the subglacial geology to palaeo-ice flow behaviour. In combination with findings from Chapter 2, a coherent pattern of episodic post-Last Glacial Maximum retreat between the Pine Island and Abbot glacial troughs across the inter-ice stream ridge is revealed by the landform information, from which uniform retreat across the entire eastern Amundsen Sea Embayment is inferred. The same episodic style of retreat is also evident for a formerly unstudied part of the Amundsen Sea shelf offshore the Hobbs Coast presented in Chapter 4, as here the analysis and interpretation of marine geophysical and geological data reveal a large grounding-zone wedge recording a prolonged grounding line stabilization phase after the West Antarctic Ice Sheet reached the continental shelf edge during the last maximum extent. The initial retreat here is demonstrated to have been initiated at a pre- or early Last Glacial Maximum stage with deglaciation of inner shelf regions completed by ~12.9 cal. ka BP. Set in the context of other studies, a diachronous initial retreat of West Antarctic Ice Sheet grounding lines is indicated, which is discussed as a possible response to different local settings. This thesis will ultimately help to better understand West Antarctic Ice Sheet dynamics during and since the Last Glacial Maximum. The new information will significantly add to a hitherto sparse database of previous work, helping to test, validate, and improve ice sheet models in the vital region of the Amundsen Sea. Only by enhancing their ability to simulate past ice sheet configurations more accurately will more reliable predictions of the future evolution of these dramatically changing parts of the West Antarctic Ice Sheet be possible.

The central question of this thesis is: what is hidden under the ice sheet of Antarctica? To unravel the tectonic structure and to study the geodynamic evolution of Antarctica are not only of fundamental geological interest. Knowledge of the amalgamation and break-up of supercontinents provides basic information for studying the evolution of the climate and the biosphere during Earth s history. Furthermore, knowledge about the tectonic structure of Antarctica is essential for estimating its crustal heat flow, a key parameter when modeling ice flow and future changes of ice sheets. The Antarctic ice sheet is mostly several kilometers thick, and rocks crop out of it in only a few locations to allow direct geological sampling. None of these locations is in the innermost parts of the continent. Hence, regional geophysical reconnaissance and a correlation of its data with geological findings are required for unraveling the tectonic structure of Antarctica. In recent decades, the Jurassic break-up process of Gondwana has been reconstructed based on analyses of the magnetic striping pattern of the oceanic crust, making it apparent that East Antarctica was positioned centrally in this supercontinent between Africa, India, Australia, and New Zealand throughout Paleozoic and Early Mesozoic times. However, fundamental data about the tectonic structure of East Antarctica that would be needed to better understand the assembly of Gondwana in Late Proterozoic and Early Paleozoic times, as well as about earlier collision and break-up processes, are still missing. This study pursues the question of whether the interior of East Antarctica is composed of one or many crustal fragments. Its method objective is to search for the courses of supraregional shear zones and the positions of crustal blocks and their boundaries. For this purpose, the Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung (AWI) has undertaken systematic airborne geophysical surveying in the region of Dronning Maud Land (DML) and Coats Land over the last decades. The data set includes ice-penetrating radar, aeromagnetic and areogravity measurements. Interpretation of the magnetic and gravity anomaly pattern caused by the rocks below the ice and the resulting conclusions are based on geological findings in DML and adjacent regions in East Antarctica and southern Africa. One substantial result of this thesis for understanding of the tectonic structure of East Antarctica is the discovery of a distinct aerogeophysical province in southeastern DML. It is concluded that the magnetic and gravity anomaly data of this province can be regarded as the signature of a discrete crustal fragment. This southeastern DML province is interpreted to have collided with southern Africa as part of the Pan-African amalgamation of Gondwana, during which the Grenvillian Namaqua-Natal-Maud belt was deformed within central DML. The prominent Forster Magnetic Anomaly might represent the suture zone of this collision. Aeromagnetic data of the Geodynamic Evolution of East Antarctica (GEA) project reveal an eastward extent of the southeastern DML province into the southern Sør Rondane region, while several smaller terranes, shear zones, and tectonic boundaries are mapped farther north. It is shown how the airborne geophysical data invite an interpretation of the central Sør Rondane region as a distinct tectonic unit with a presumably increased crustal thickness. Furthermore, the eastern boundary of the BLM craton in Coats Land is mapped and its prominent magnetic anomaly pattern is shown to be unique within DML and southern Africa, raising the question of the provenance of this crustal fragment, which appears not to have been high-grade reworked during the Pan-African orogeny. In contrast, the Kohnen lineament is interpreted as a Pan-African shear zone with similarities to the outcropping Heimfront shear zone. In addition, a detailed study and modeling of the Giæver Magnetic Anomaly show that it is likely to be the signal of a shallow subcrop of banded iron formation. With the multiplicity of these findings, results, and conclusions, this thesis contributes significant new knowledge and future prospects for unraveling the tectonic structure and the geodynamic evolution of East Antarctica.

An accretionary wedge evolves wide extended, flat and with a characteristic thrust system, if the wedge décollement is located in a viscous evaporite. The deformation processes of such wedges are complex and until now not fully understood. Therefore, in this present work 2D numerical sandbox experiments are developed in which an incoming sediment sequence is accreted against a fixed vertical wall due to a moving box bottom. The experiments contain a brittle incoming sequence in which either a brittle Mohr Coulomb layer or a viscoelastic-plastic layer (Burger s rheology) is embedded. The first study focuses on the differences which occur in the mechanics of two wedge experiments if either a weak viscoelastic-plastic or a low-friction brittle layer is embedded between two high friction brittle layers. To find out the viscosity under which the wedge deforms most likely as it would grow on top of an evaporite, the second study analyzes the effects of different viscous materials on wedge mechanics. Finally, the calibrated model is used to study the effects of different incoming sediment thicknesses on the accretion process.

The relations between climate, tectonics and topographic changes are still not fully understood. During the Late Cenozoic, the glacial cycles affecting the European Alps are held responsible for a strong increase in Alpine relief. Detrital samples of the circum-Alpine foreland depocenters were analyzed with detrital thermochronology, namely the apatite fission track and (U-Th-Sm)/He dating methods. The new thermochronological data contradict a long-term exhumational equlibrium for the Central and Western Alps, as frequently postulated in Alpine literature. In fact, distinct Alpine regions differ severely in their exhumation pattern. Also the drainage pattern was more complex than previously assumed, with a proto-Rhine draining via the Rhine Graben towards the North Sea in Pliocene times.

The main representatives of ultraslow spreading ridges are the Arctic Ridge System (ARS) and the Southwest Indian Ridge (SWIR). As earthquakes indicate active crustal accretion, monitoring the seismicity provides information about the mechanical state of the lithosphere. The Lena Trough, part of the ARS, spreads obliquely and amagmatic. I relocalized the globally detected earthquakes to show the spatial distribution of the seismicity along the rift axis. During two surveys, our working group recorded the microseismicity of Lena Trough with seismic arrays deployed on ice floes. The second case study concerns the magmatic Orthogonal Supersegment of the SWIR. I accessed the regional dataset of the Neumayer seismic array in Antarctica lying in a distance of ~2100 km to the study area. The dataset contains 743 earthquakes and clearly shows four swarms occurring at an assumed volcanic centre. The new datasets allow a comprehensive evaluation lowering the detection threshold compared to the global station network. Active accretion episodes can be monitored in greater detail showing the spreading mechanisms at contrasting amagmatic and magmatic ridge segments.

Serpentinization, steatitization, and rodingitization are consequences of seawater reaction with lithospheric mantle. These processes take place coevally within the oceanic lithosphere and are related to circulation pathways, lithologic makeup of rocks along the flow path, fluid flux, and temperature. While the boundary conditions are set by the history of magmatic and tectonic accretion of the lithosphere, fluid-rock equilibria determine what reactions take place and where in the system. Petrologists are challenged to determine the fundamental phase relations and fluid-rock interactions in order to better understand how the physical properties of the oceanic lithosphere develop and how the water-rock interactions contribute to providing energy for deep-sea microbial ecosystems independent of photosynthesis. How is hydrogen formed during serpentinization? How much of it is formed? Why are some gabbroic veins rodingitized, while others are not? What is causing steatitization? These are basic questions in oceanic petrology that have not been comprehensively addressed. The purpose of this thesis is to change this.

Geophysical and geological investigations in the Arctic region are very important for a betterunderstanding of the present day global climate. Changes in global climate is one of the highlyspeculative aspect in the Northern Hemipsphere, especially the onset of glaciation. Advancesand retreats of grounded ice sheets during glacial-interglacial times play an important role interms of the deposition of large sediment deposits. Depositional pattern on the continentalslope and rise reflect interactions between the effects of ice sheet fluctuations, mass transportprocesses and bottom currents. The main focus of this thesis is the sedimentation historyalong the East Greenland margin in late Cenozoic times. Different seismic reflection surveysgathered between 1997 and 2003, represent the sedimentary structure along this margin fromthe shelf up into the deep sea area. A for the first time an applied seismostratigraphy onthe Northeast Greenland margin made it possible to differenciate between glacial (youngerthan middle Miocene) and pre-glacial (older than middle Miocene) sediment units. Glacialadvances and retreats appear not synchronous along the continental margin. Therefore, eithernorth of 70 degrees N the extension of the shelf by glacial erosion seems to be more intensive likeon the Southeast Greenland margin or the onset of glaciation started earlier in the norththan in the south. The results of the modelling of different sediment maps enables a lotof varibiabilities in the sediment supply along the continental margin. The greatest totalsediment amount is observed in the prolongation of glacial drainage outlets like the ScoresbySund. Other influences on the sediment thickness along this margin are caused by tectonicelements, the opening history of the basins and the existing current activity. The glacialsediment thickness map, however, enables the highest amount of glacial sediments in thenorthern Molloy Basin (around 1500 m), probably caused by mass transport from the ArcticOcean. Analyses of the deep sea sediment structure provide an insight into a well-laminatedsedimentary succession within the Molloy Basin, which has been interpreted as currentcontrolledaccumulation. An outflow of Arctic Ocean bottom water and an inflow of NorthAtlantic deep-water could be identified. Especially, the levee structure west of the channelpoints to an intensification of current activity since around 5 Ma, also supported by turbiditychannel activity in the deep Greenland Basin.This study demonstrates the interaction between sediment accumulation, climatic changesand changes in ocean circulation. The results provide a basis for a proposal of future OceanDrilling Programms and further geological studies on this margin.

Low-temperature thermochronology owns the unique potential to derive rates of cooling, exhumation and denudation (erosional and tectonic). Furthermore it bears information about palaeotopography. This thesis comprises five low-temperature thermochronological studies conducted in the Western and Central Alps, i.e., one study in the eastern Lepontine dome and four studies along orogen-perpendicular transects through the Western and Central Alps. Main objectives of these studies are: (1) To unravel the structural-kinematic and exhumation history of the investigated regions, and (2) to estimate the shape of palaeo-isotherms under given boundary conditions. Three transects along tunnels (Mont Blanc, Lötschberg and Gotthard) and corresponding surface profiles were sampled in the external crystalline massifs (ECM) of the Mont Blanc, Aar and Gotthard. Sampling of the Lepontine dome was applied on a broader spatial scale. Samples were dated with the apatite and zircon fission track method (AFT and ZFT, respectively) and with the apatite (U-Th)/He method (AHe), which record the cooling of rocks between 330 and 40°C. The resulting two-dimensional sample transects along the tunnels were used to estimate the shape of palaeo-isotherms and to derive lateral and temporal differences in exhumation rates. Thermochronological data, especially from near vertical age-elevation profiles, were used to derive the Late Neogene exhumation history of the investigated regions in the external massifs and of the Lepontine dome. The exhumation histories were compared with estimates for adjacent regions and used to investigate the impact of climatic and tectonic forcing on the evolution and exhumation of the Alpine orogen. Main conclusions from the individual studies are: Mont Blanc transect Thermal modeling of AFT and AHe data suggests that the Mont Blanc massif (MBM) was exhumed episodically, with rapid exhumation (2.5±0.5 km/Myr) before 6 Ma, followed by an episode of slow exhumation and again a period of fast exhumation (>1 km/Myr) after ~3 Ma. The MBM is the only ECM that experienced fast exhumation at ~6.5 Ma, possibly related to NW and minor SE directed thrusting of the MBM. I propose that the acceleration in exhumation rates of the MBM after ~3 Ma is caused by rapid valley incision related to beginning Alpine glaciation, implying that the recent relief of the MBM is a young feature. Lötschberg transect The data show a constant exhumation of the SW Aar massif with a rate of ~0.5 km/Myr for the last 10 Myr, increasing only in the southern area close to the Rhône-Simplon fault around 3.5 Ma to values up to 1.2 km/Myr. Acceleration of exhumation in the south is most likely triggered by increased orogen-perpendicular extension causing tectonic denudation along the south dipping Rhône-Simplon fault. Climatic forcing, especially the intensification of Alpine glaciation around 0.9 Ma has also contributed to the observed exhumation, but the magnitude of this impact can not be resolved with the data. Gotthard transect Thermochronological ages along the sampled Gotthard transect are very uniform, suggesting that vertical movements along distinct fault structures within and between the Aar massif (AM) and Gotthard massif (GM) can be neglected since ~15 Ma. Age-elevation profiles of ZFT and AFT data of the central AM and GM suggest fast exhumation (~1 km/Myr) around 15 Ma decreasing to a steady, uniform and moderate exhumation with a rate of ~0.5 km/Myr since ~9 Ma. Fast exhumation at ~15 Ma is probably related to continuing indentation of the Adriatic wedge, which resulted in thrusting and exhumation of the external massifs. Since ~9 Ma, the central AM and GM are maybe in a long-term exhumational steady state. Isostatic movements caused by unloading effects due to glacier retreat and/or enhanced erosion, however, led to short term fluctuations of rock uplift rates, not resolvable by our data. Thermochronological data (ZFT, AFT) within the Gotthard tunnel show no correlation with topography, suggesting that (palaeo-) topography-induced perturbations of isotherms were small under given boundary conditions (i.e., topographic wavelength = 12 km, relief = 1.7 km, exhumation rate = 0.5 km/Myr). A new 3D thermal model was developed and used for investigating the potential impact of different input parameters (topography, conductivities, heat production, exhumation rates) on shape of isotherms and resulting thermochronological data. Modelling reveals a strong dependence of the shape of isotherms and thermochronological ages on spatial variable heat production and exhumation rates. In the case of the Gotthard transect the influence of the topography can be neglected for the interpretation of thermochronological data, as well as in most other regions in the Alps with similar relief. Lepontine dome Thermochronological data of the eastern Lepontine dome was used to investigate the exhumation history and activity of the Forcola fault. The data reveal episodic exhumation of the eastern Lepontine dome with fast exhumation from ~23-16 Ma, 12-10 Ma and 5-4 Ma. The exhumation is directly linked to the onset of Miocene lateral extension and related activation of the Forcola fault. Fast exhumation between 5 and 4 Ma coincide with an increase in foreland basin deposits. Slowing down of exhumation after 4 Ma is consistent with the proposed transition from orogenic construction to orogenic destruction and related shift of active deformation into the interior of the Alpine orogen. To sum up, all three sampled tunnel transects show no correlation of palaeo-isotherms with topography. This observation has to be interpreted in terms of the topography induced perturbation of isotherms, taking into account that obviously the present topography and relief is a very young feature (< 3 Ma). Accompanied thermal modelling additionally demonstrates that other parameters (exhumation rate, heat production), beside topography, also strongly influence the shape of near-surface isotherms. Reasons why no correlation of palaeo-isotherms with recent topography is observable are different for the tunnel transects: The relief along the Mont Blanc tunnel was less pronounced at the time given by the thermochronometer. Along the Lötschberg tunnel strong spatial differences in exhumation rates control the thermochronological age pattern, and consequently the topographic effect is not observable. Along the Gotthard tunnel ages are controlled by several spatially varying parameters (including topography, exhumation and heat production), which result in apparent flat palaeo-isotherms. Comparing exhumation histories from the appended studies, complemented by published exhumation histories of adjacent regions, I conclude that: (1) Comparing the exhumation rates of all ECM shows that the Messinian base level drop (~5.5 Ma) and the intensification of precipitation caused by an increase in the Atlantic Gulf Stream (~4.6 Ma) did not affect the exhumation rates of the external Alps. (2) All ECMs, except the central Aar and Gotthard massifs, show an increase in exhumation rates at ~3 Ma. I interpret this as the result of beginning Alpine glaciation and normal faulting along orogen-parallel faults. Niedrig-Temperatur-Thermochronologie erlaubt es Raten der Abkühlung, Exhumation und der Denudation (durch Erosion und Tektonik) zu bestimmen. Außerdem lassen sich Informationen über die Paläo-Topographie ableiten. Die vorliegende Doktorarbeit beinhaltet fünf Niedrig-Temperatur-Thermochronologische Arbeiten über die westlichen und zentralen Alpen, d.h. eine Arbeit im Lepontine Dome und vier Arbeiten entlang orogen-senkrechter Profile in den westlichen und zentralen Alpen. Zielsetzungen dieser Arbeiten waren: (1) Die Exhumationsgeschichte der untersuchten Arbeitsgebiete zu rekonstruieren, und (2) den Verlauf von Paläo-Isothermen unter gegebenen Rahmenbedingungen abzuschätzen. Drei Tunnelprofile (Mont Blanc, Lötschberg und Gotthard) und ihre entsprechenden Oberflächenprofile wurden in den externen Kristallin-Massiven (ECM) des Mont Blanc, Aar und Gotthard beprobt. Die Beprobung im Lepontine Dome erfasste ein größeres Areal. Die Proben wurden mit der Apatit und Zirkon Spaltspurmethode (AFT und ZFT) und mit der Apatit (U-Th)/He Methode (AHe) datiert, mit welchen sich die Abkühlung von Gesteinen von 330 auf 40°C rekonstruieren lässt. Die resultierenden zwei dimensionalen Probenprofile entlang der Tunnel wurden dazu benutzt, um den Verlauf von Paläo-Isothermen abzuschätzen und laterale und temporale Unterschiede in Exhumationsraten zu bestimmen. Thermochronologische Daten, besonders von fast vertikalen Alters-Höhen-Profilen, wurden benutzt um die Spät-Neogene Exhumationsgeschichte der Untersuchungsgebiete in den ECM um im Lepontine Dome herzuleiten. Die resultierenden Exhumationsgeschichten wurden mit denen benachbarter Gebiete verglichen, um den Einfluss von klimatischen und tektonischen Kräften auf die Entstehung und die Exhumation des alpinen Orogens zu quantifizieren. Die wichtigsten Schlussfolgerungen der Einzelarbeiten sind: Mont Blanc Profil Thermische Modellierung von AFT und AHe Daten zeigen, daß das Mont Blanc Massiv (MBM) episodisch exhumiert wurde: sehr schneller Exhumation (2.5±0.5 km/Myr) vor 6 Ma, gefolgt von einer Phase sehr langsamer Exhumation und wiederum gefolgt von einer Phase schneller Exhumation (>1 km/Myr) nach ~3 Ma. Das MBM ist das einzige ECM, welches diese sehr schnelle Exhumation um etwa 6.5 Ma zeigt, die vermutlich im Zusammenhang mit NW und SE Überschiebung des MBM steht. In dieser Arbeit schlage ich vor das die beschleunigte Exhumation seit ~3 Ma in Zusammenhang mit einer schnellen Taleintiefung steht, die durch die beginnende alpine Vergletscherung verursacht wurde. Damit ist das Relief des MBM sehr jung. Lötschberg Profil Die Daten zeigen eine konstante Exhumation des SW Aar Massivs mit einer Rate von ~0.5 km/Myr für die letzen 10 Myr an, welche nur im südlichen Teil des Profils nahe der Rhône-Simplon Störung um 3.5 Ma auf Raten bis 1.2 km/Myr anstiegen. Dieser Anstieg in den Exhumationsraten wurde vermutlich durch orogen-senkrechte Extension ausgelöst, die zu tektonischer Denudation entlang der Rhône-Simplon Störung führte. Klimatische Kräfte, besonders die Intensivierung der alpinen Vergletscherung um 0.9 Ma haben ebenfalls zur beobachten Exhumationsgeschichte beigetragen, allerdings kann ihr Anteil an den Exhumationsraten nicht mit den vorliegenden Daten quantifiziert werden. Gotthard Profil Thermochronologische Alter entlang des Gotthard Profils sind sehr einheitlich, was nahe legt das seit ~15 Ma vertikale Bewegungen entlang von Störzonen innerhalb und zwischen dem Aar Massiv (AM) und dem Gotthard Massiv (GM) vernachlässigbar klein sind. ZFT und AFT Alters-Höhen Profile im zentralen AM und GM zeigen ein schnelle Exhumation (~1 km/Myr) um 15 Ma an, welche mit der Zeit abnahm und seit etwa 9 Ma konstant bei ~0.5 km/Myr lag. Die schnelle Exhumation um 15 Ma hängt vermutlich mit der andauernden Einrückung des adriatischen Keils zusammen, welche zu einer Überschiebung und Exhumation der ECM führte. Vermutlich seit ~9 Ma sind die Exhumationsraten im zentralen AM und GM in einem stationären Zustand. Allerdings verursachten isostatische Bewegungen induziert von Entlastungen (Gletscher Rückgang, gesteigerte Erosion) kurzzeitige Schwankungen in Hebungsraten, die nicht mit unseren Daten aufgelöst werden können. Die thermochronologischen Daten (AFT und ZFT) entlang des Gotthard Tunnels zeigen keine Korrelation mit der Topographie, welches andeutet das die (paläo-) topographisch-induzierte Aufwölbung von Isothermen gering war unter den gegebenen Rahmenbedingungen (d.h., topographische Wellenlänge = 12 km, Relief = 1.7 km, Exhumationsrate = 0.5 km/Myr). Ein neues drei-dimensionales thermisches Model wurde entwickelt und für die Abschätzung des möglichen Einflusses verschiedener thermischer Parameter (Topography, Konduktivität, Wärmeproduktion, Exhumationsrate) auf die Aufwölbung von Isothermen und resultierender thermochronologischen Ater benutzt. Die Modellierungen zeigen einen großen Einfluss auf den Verlauf von Isothermen in Abhängigkeit von räumlich variierender Wärmproduktions- und Exhumationsraten. Im Falle des Gotthard Profils kann der Einfluss der Topographie auf die Isothermen und damit auf die Interpretation von thermochronologischen Daten vernachlässigt werden, genau wie in den meisten alpinen Gebieten mit ähnlichen Relief. Lepontine Dome Thermochronologische Daten vom östlichen Lepontine Dome wurden benutzt um die Aktivität der Forcola Störung und die Exhumationsgeschichte des Untersuchungsgebietes zu untersuchen. Die Daten zeigen eine episodische Exhumation des östlichen Lepontine Domes an, mit schneller Exhumation zwischen ~23-16 Ma, 12-10 Ma und 5-4 Ma. Die Exhumation ist direkt mit der Miozänen lateralen Extension und der Aktivität der Forcola Störung gekoppelt. Schnelle Exhumation zwischen 5 und 4 Ma deckt sich zeitlich mit einem Anstieg in Vorlandbecken-Ablagerungen. Verlangsamte Exhumation nach 4 Ma ist im Einklang mit einem postulierten Übergang von orogenen Konstruktion zu orogenen Destruktion and damit in Zusammenhang stehender Verschiebung der aktiven Deformationsfront ins Innere des alpinen Orogens. Zusammenfassend läßt sich sagen, daß abgeleitete Paläo-Isothermen der drei untersuchten Tunnelprofile keine Korrelation mit der Topographie zeigen. Für die Interpretation dieser Beobachtung bezüglich des Einflusses der Topographie auf die Aufwölbung von Isothermen muß berücksichtigt werden, daß die heutige Topographie und das heutige Relief sehr jung sing (< 3 Ma). Die begleitende Modellierung zeigte außerdem, daß andere Parameter außer der Topographie (z.B. Exhumation und Wärmeproduktion), einen starken Einfluß auf den Verlauf von oberflächennahen Isothermen haben. Die Gründe weshalb keine Korrelation zwischen den Paläo-Isothermen und der heutigen Topographie gefunden wurde sind verschieden für die einzelnen Tunnelprofile: Das Relief am Mont Blanc Tunnel war weniger stark ausgeprägt während der Zeit als die Proben die für die benutzten Thermochronometer sensitiven Isothermen durchliefen. Entlang des Lötschberg Tunnels kontrollierten stark räumlich variierende Exhumationsraten die thermochronologische Altersverteilung, und folglich ist der Effekt der Topographie nicht zu erkennen. Die Alter entlang des Gotthard Tunnels sind das Resultat von verschiedenen räumlich variierenden Parameter (Topographie, Exhumation und Wärmeproduktion), die zu scheinbaren flachen Paläo-Isothermen führten. Vergleicht man die Exhumationsgeschichte aus den untersuchten Arbeitsgebieten, ergänzt durch publizierte Exhumationsgeschichten benachbarter Gebiete, so kann man folgende Schlußfolgerungen ziehen: (1) Alle ECM zeigen das die Messininsche Salinitätskrise (~5.5 Ma) und die Intensivierung der Niederschlags verursacht durch einen erhöhten Atlantischen Golfstrom (~4.6 Ma) keinen Einfluß auf die Exhumationsraten der externen Alpen haben. (2) Mit Ausnahme des zentralen AM und GM zeigen alle ECM eine Steigerung in den Exhumationsraten um 3 Ma. Diese Steigerung resultiert aus der beginnenden alpinen Vergletscherung und abschiebender Bewegungen entlang von orogen-parallelen Störungen.