Gohl, Karsten
Lade...
Preferred name
Gohl, Karsten
Official Name
Gohl, Karsten
5 Ergebnisse
Gerade angezeigt 1 - 5 von 5
- Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, From crustal structure to plate kinematics : the role of Large Igneous Provinces in the Pacific Ocean(2016-04-14); ; ; The bathymetry of the Pacific Ocean is dominated by three Large Igneous Provinces (LIP): the Ontong Java Plateau, the Hikurangi Plateau and the Manihiki Plateau. Taylor (2006) proposed their joined emplacement as one "Super"-LIP Ontong Java Nui in the early Cretaceous. Petro- logical and geochemical data point to this scenario, but geophysical evidence is sparse. To evaluate the hypothesis of Ontong Java Nui, refraction/wide-angle reflection seismic data was collected in 2012, during the RV Sonne cruise So-224 across the two main sub-provinces of the Manihiki Plateau. The modeling and interpretation of P-wave velocity, S-wave velocity and density profiles across the Manihiki Plateau along with available seismic reflection data aims to enhance our understanding of the crustal structure of the Manihiki Plateau and improve the plate kinematic reconstruction of the western Pacific region during the Cretaceous. If the hypothesis is correct, the Manihiki Plateau exposes break-up margins to all other LIPs of Ontong Java Nui. The Manihiki Plateau itself is fragmented into multiple sub-provinces. The two largest sub-provinces, the High Plateau and the Western Plateaus have been studied in- tensively in this experiment. The crustal structure of the High Plateau is comparable to other LIPs with a high velocity zone (P-wave velocities >7.3 km/s) in the lower crust and a basaltic to gabbroic crust. The crustal thickness is 20 km. Secondary magmatic phases are strong on the High Plateau expressed in multiple volcanic centers. The Danger Islands Troughs are a series of pull-apart basins, which separate the High Plateau from the Western Plateaus. These plateaus have been subject to massive tectonic deformation such as the gradual decrease in crustal thickness from 17.3 km in the East to 9.1 km in the West. Secondary volcanism is limited to fracture zones and low volume seamount volcanism. Since the crustal structure of the Western Plateaus points to a joined emplacement, the "Super"- LIP can be reassembled. The data also provides further evidence for a eastern and a northeastern continuation of the Manihiki Plateau by the sudden termination of the high velocity zone in the lower crust towards the East. It has been accounted for subducted LIP-parts, the rotation of LIP fragments such as the Hikurangi Plateau, crustal stretching invoked during the break-up and the crust emplaced during secondary magmatic stages. This calculates to an approximated initial size of Ontong Java Nui of 1.1. % of the Earth's s surface. Based on this information I reconstructed the "Super"-LIP Ontong Java Nui and modeled its break-up during the Cretaceous Normal Superchron. The initial emplacement of Ontong Java Nui can be explained by the interaction of a mantle plume with the Pacific-Phoenix ridge resulting in different crustal thicknesses throughout the plateau. I modeled the motion of different fragments of Ontong Java Nui using mapped fracture zones, traces of former plate boundaries and refined kinematic rotation poles of the western Pacific. Paleogene and Neogene intraplate tectonic activity occurred within the Ellice Basin between the Ontong Java Plateau and the Manihki Plateau and on the Manihiki Plateau itself. The eastern and northeastern fragments of the Manihiki Plateau have been captured by the Phoenix and Farallon Plate, respectively. The eastern fragment subducted analog to the southern Hikurangi Plateau at the eastern Gondwana margin in today's s Bellingshausen Sea and Palmer Land region during the Mid-Cretaceous, possibly flattening the slab of the subduction zone. The northeastern fragment collided with the South American craton during the Paleocene. In this amagmatic trench setting, oceanic terranes were accreted to the craton building up today's s northern Andes. The Pinà oà n formation of Colombia and Ecuador is a possible candidate to be a remnant of the lower crust of the Manihiki Plateau.Dissertation502 203 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Geothermal Heat Flow in the Amundsen Sea Sector of West Antarctica(2018-11-22); ; ; The ice sheet inWest Antarctica is underlain by theWest Antarctic Rift System, which yields critical geological boundary conditions. The bedrock geology and the crustal structure of the rift system may influence the dynamics of the overlying glaciers, which in turn affect the stability of the ice sheet. Previous geophysical surveys have traced the West Antarctic Rift System from the Ross Sea to the Bellingshausen Sea and compared it to other major continental rift zones, such as the East African Rift System or the Basin and Range Province. While the rift system in the Ross Sea sector is relatively well understood, the remaining part of the rift system surrounds a higher degree of uncertainty. Young, continental rift systems, such as the West Antarctic Rift System, are associated with high geothermal heat flow and elevated lithospheric geotherms. In-situ temperature observations of geothermal heat flow are extremely sparse in Antarctica, but present crucial thermal boundary conditions ice sheet models and related sea level rise predictions. Moreover, temperature measurements are urgently required to study geodynamic and tectonic processes, subglacial lakes, hydrologic networks and ecosystems beneath ice sheets, that remain largely unexplored. Indirect methods, that estimate geothermal heat flow on regional to continental scales show poor correlation, which leads to ambiguous results in e.g. ice sheet models. Scientifically, this project aims at contributing to the overall knowledge of the thermal state of the crust in the Amundsen Sea Sector. Within the context of this thesis, a novel suit of in-situ temperature measurements were collected in the Amundsen Sea Embayment during RV Polarstern expedition PS75 (2010) and PS104 (2017). A novel magnetic anomaly grid is further presented, which includes aeromagnetic data collected during RV Polarstern expedition PS104, as well as previous aeromagnetic surveys, and forms the base for investigations of the thermal state of the crust. By Curie depth estimates, based on spectral analysis of the magnetic anomaly data and numerical models in 2D and 3D, the spatial distribution of geothermal heat flow and the thermal architecture of the crust is examined. The main outcomes of the thesis are local estimates of geothermal heat flow of 60 mWm2 to 90 mWm2, which is likely biased towards higher values due to the temperature variability in the water column. Indirect estimates from numerical models in contrast point towards elevated ( 90 mWm2) and locally high ( 90 mWm2) geothermal heat flow. In summary, the findings from the current thesis represent a significant advancement towards understanding of geothermal heat flow in the Amundsen Sea Sector of West Antarctica.Dissertation368 202 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Palaeoenvironment of the Weddell Sea and Amundsen Sea - eastern Ross Sea basins, Antarctica: Insights from comprehensive seismostratigraphic analysis(2014-05-19); ; ; 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.Dissertation402 135 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Glacially related and bottom current controlled sedimentation processes on the West Antarctic continental margin - Interpretations derived from seismic reflection investigations(2006-06-29); ; ; The advances and retreats of grounded ice on the Antarctic continental shelf during glacial-interglacial cycles led to the deposition of large sediment deposits. Depositional patterns on the continental slope and rise reflect interactions between the effects of ice sheet fluctuations, mass transport processes and bottom currents. The central element of this thesis is the study of the late Cenozoic glacial history of the South Pacific continental margin of West Antarctica by interpreting the record of marine sediments there, with focus on the sedimentary successions of the outer continental shelf, slope and rise. The thesis presents the results of seismic stratigraphic analyses of multi-channel and single channel seismic reflection profiles collected on the continental margin during the course of several cruises since 1986. Seismic stratigraphic patterns are interpreted with reference to recent sedimentation models in order to differentiate between pre-glacial and glacially-influenced sediment units.Dissertation282 97 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Crustal evolution of the submarine plateaux of New Zealand and their tectonic reconstruction based on crustal balancing(2007-11-23); ; ; The last supercontinent fell into pieces with the break-up of Gondwana. In this context, the separation of the microcontinent of New Zealand from Antarctica is a jigsaw puzzle of many pieces. Its parts lay at the convergent margin of East Gondwana, which changed into a divergent margin within a geologically short time. That is why the microcontinent of New Zealand experienced different tectonic regimes and phases of the Wilson cycle. Although it is a good object of investigation due to its changing history, remarkably little is known about the submerged parts of the microcontinent. Knowledge of the magmatic-tectonic development of the submarine plateaux such as Campbell Plateau and Chatham Rise will improve the understanding of the processes that led to the late Gondwana break-up, and, in turn, lead to better reconstructions of East Gondwana, as Zealandia is a key piece in plate-kinematic reconstructions of this part of Gondwana.The central part of this thesis deals with the separation process of Zealandia from Antarctica leading to an improved reconstruction of New Zealand with emphasis on the submarine plateaux. Bounty Trough separating Chatham Rise from Campbell Plateau, and the Great South Basin separating Campbell Plateau from the South Island are investigated with seismic refraction and reflection methods. They are interpreted jointly with magnetic and gravity data. The results of crustal thickness modelling based on satellite gravity data are combined with existing information about crustal thickness of Zealandia. With these data, a crustal thickness grid is calculated which creates the basis for a novel technique for plate-kinematic reconstructions in areas of crustal thinning and in the absence of magnetic seafloor anomalies. This reconstruction consists of crustal balancing to compensate for extension within basins and troughs.The seismic refraction and reflection survey across the Bounty Trough shows a strongly thinned crust in the trough. Zones of high P-and S-wave velocities were found in the lower crust shows. Comparison of the P-wave model and a Poisson's ratio model with rock type diagrams leads to a compositional model of the crust. The joint interpretation of all models suggests that extension in the Bounty Trough proceeded until seafloor spreading in the Middle Bounty Trough began. Geophysical data from the Great South Basin show underplating beneath the Central Campbell Plateau and crustal thinning in the basin, to a lesser extent than in Bounty Trough. Comparison of the seismic data with existing magnetic data across the Great South Basin (Stokes Magnetic Anomaly System - SMAS) and the Campbell Plateau (Campbell Magnetic Anomaly System - CMAS) resulted in the conclusion that these anomaly systems have different origins or histories. Contrary to the results of this thesis, previous investigations assumed a common origin of SMAS and CMAS. Plate-kinematic reconstruction on the base of observations and interpretations combined with existing and modelled crustal thickness shows that extension in Bounty Trough and Great South Basin as well as in New Caledonia Basin was significantly less than previously assumed. The novel technique for plate tectonic reconstructions in thinned continental crust presented in this thesis has the potential to improve plate-kinematic reconstructions for early break-up settings and failed rift systems with stretched continental crust worldwide.Dissertation358 113