ALBERT

Beschreibung: The Eifel is the youngest volcanic area of Central Europe. The last eruption occurred approximately 11000 years ago. Little is known about the deep origin and the mechanism responsible for the Eifel volcanic activity. Earthquake activity indicates that the Eifel is one of the most geodynamically active areas of Central Europe. In this work the receiver function method is used to investigate the upper mantle structure beneath the Eifel. Data from 96 teleseismic events (mb 〉 5.2) that were recorded by both permanent stations and a temporary network of 33 broadband and 129 short period stations had been analyzed. The temporary network was operating from November 1997 till June 1998 and covered an area of approximately 400x250 km^2 centered on the Eifel volcanic fields. The receiver function analysis reveals a clear image of the Moho and the mantle discontinuities at 410 km and 660 km depth. Average Moho depth is approximately 30 km and it shows little variation over the extent of the network. The observed variations of converted waveforms are possibly caused by lateral variations in crustal structure, which could not resolved by it receiver functions}. Inversions of data and migrated it receiver functions} from stations of the central Eifel array suggest that a low velocity zone is present at about 60 to 90 km depth in the western Eifel region. There are also indications for a high velocity zone around 200 km depth, perhaps caused by dehydration of the rising plume material. The results suggest that P-to-S conversions from the 410-km discontinuity arrive later than in the IASP91 reference model. The migrated data show a depression of the 410 km discontinuity of about 20 km, which correspond to an increase of temperature of about 140° Celsius. The 660 km discontinuity seems to be unaffected. This indicates that no mantel material rises up from directly below the 660 km discontinuity in the Eifel region or the Eifel-Plume has its origin within the transition zone.

Beschreibung: Der Scientific Technical Report (STR) 03/08 ist die teilweise überarbeitete Diplomarbeit des Autors, welche im November 2002 am Lehrstuhl für Astronomie des Instituts für Planetare Geodäsie der Fakultät Forst-, Geo- und Hydrowissenschaften an der Technischen Universität Dresden eingereicht wurde.

Beschreibung: The work contained in this thesis considers deformations of the Earth, which are produced by the loads of the last ice-age glacial sheets. The forces the Earth sets against the surface loads are the buoyancy force of the Earth's mantle and the opposing force by the elastic flexure of the lithosphere. Because the time scale of the ice-age of some 100,000 years is short with respect to geological time scales, the viscoelastic behaviour of the Earth has to be considered. Viscoelasticity results in a retarded response of the Earth, which is observed as postglacial uplift in previously glaciated regions, 8,000 years after deglaciation. To model the buoyancy of the Earth's mantle, often a viscous incompressible fluid of homogeneous density is assumed. More recent studies consider also compressibility of the mantle material, but keep the homogeneous density. This results in an inconsistent reference state, because the self compression due to hydrostatic pressure is neglected. These models are discussed here, and the problems are shown, which arise from the description of the field equations for a viscoelastic compressible gravitating continuum in a half-space geometry. The opposing force by the elastic flexure of the lithosphere is determined by the flexural rigidity of the lithospheric plate. If we consider viscoelastic layers in the lithosphere, the flexural rigidity is reduced. Therefore, the overall thickness of a viscoelastic layered lithosphere is much larger than its effective elastic thickness deduced from assuming one elastic plate. Consequently the effective elastic thickness looses its merit for assessing the lithosphere thickness. We show, how strong effective elastic thickness and lithosphere thickness may differ, in which way the viscoelastic structure of the Earth influences this difference for glacial loads and which consequences arise for the lithospheric stress state.

Beschreibung: In Südostalaska wird eine relative Meeresspiegelabsenkung von bis zu 4 cm/ a beobachtet. Da dieses Gebiet während der letzten Kaltperiode durch das Kordillerische Eisschild bedeckt war und noch heute von Vergletscherung geprägt ist, liegt die Vermutung nahe, daß die Meeresspiegeländerungen zumindest teilweise durch isostatische Ausgleichsvorgänge hervorgerufen werden. Um diese Hypothese zu prüfen, werden für dieses Gebiet eislastinduzierte Vertikalbewegungen und Geoidänderungen mit Hilfe viskoelastischer Erdmodelle berechnet. Insbesondere werden sechs siebenschichtige Erdmodelle verwendet, die unterschiedliche Viskostitätsprofile berücksichtigen und die Bandbreite der plausiblen Lithosphärenmächtigkeiten abdecken. Das globale Lastmodell ICE-3G wird erweitert und das regionale Lastmodell AL-1 entwickelt, welches die rezente Vergletscherung Südostalaskas berücksichtigt. Weiterhin werden die Ozeane als Last einbezogen. Ein Vergleich der berechneten mit den beobachteten Meeresspiegeländerungen zeigt, daß die Beobachtungen nur zu einen geringen Anteil von wenigen Millimetern pro Jahr durch Isostasie erklärt werden können.

Beschreibung: Deformation processes in the early deformation stages of thrusting in growing fold-and-thrust belts and the role of factors controlling and localizing the deformation are still not well understood. There are only few natural examples or experimental studies to allow the identification of factors controlling initial states of deformation. In particular, the spatial interactions in curved fold-and-thrust belts or in segments striking obliquely to the convergence direction are rarely systematically examined. The Boomerang Hills Region (BHR), located at the eastern flank of the Central Andes close to the axis of the Bolivian Orocline, is an appropriate area to study such problems. There, oblique contraction is caused by a south-dipping basement interacting with a WSW-ENE to SW-NE convergence direction. In order to infer the controlling factors of deformation, the structural pattern associated with the active development of a new thrust sheet and the structural history of the adjacent foreland was examined. The detailed spatial-temporal relationships of Andean and pre-Andean structures within the BHR were investigated using a dense network of 100 reflection-seismic profiles for subsurface interpretation and structural modeling. In addition, satellite images and drainage pattern were interpreted to infer neotectonic activity. Modeling techniques included cross section balancing for validation and quantification of geological processes, horizon unfolding for kinematical interpretation, and critical taper estimates to derive the possible dynamic status. Results show that the main factor controlling the evolution of the Boomerang Hills Thrust Unit and the eastern flank of the Bolivian Orocline are paleogeographic features. The crystalline basement of the BHR comprises an inherited structure of several syn- and antiforms. Some of these structures were partly reactivated as minor reverse faults with associated small folds in the sedimentary cover at an early stage of the Tertiary foreland basin evolution. Basement faulting is probably a result of spatial problems linked to the initiation of a foreland basin in a heterogeneous crust. WNW-ESE striking normal faults were active in the foreland of the BHR in the Late Tertiary and show maximum activity during the intermediate state of foreland basin sedimentation. Further to the north, closer to the Brazilian Craton, normal faults are presently active. Foreland extension sums to 1.1%-1.5% and results from minor flexural extension due to bending of the Brazilian Shield lithosphere through Andean orogenic loading. The southern part of the BHR is represented by a young, evolving thrust sheet. Two zones can be differentiated along the Andean deformation front: (1) a W-E to NW-SE-striking frontal segment of predominantly orthogonal shortening, comprising a thrust / anticline system and accommodating at least 1400- 2000 m horizontal shortening on the basal decollement ; (2) A WSW-ENE-striking lateral zone of oblique shortening comprised by a complex system of thin-skinned strike-slip faults and minor folds. The deformation front always follows a pronounced edge in the topography of the top basement surface close to the boundary of the Paleozoic basin. Usually, faults are located close to asperities in the top basement surface; fold axes trend parallel to the contours of basement depth. The orientation of the deformation front as well as the laterally varying structural style is the result of deformation localization and strain partitioning. Because of the impossibility to accommodate non-orthogonal contraction by oblique faulting close to the surface, strain partitioning must occur along the deformation front. Consequently, a N 35°E thrusting direction is divided into orthogonal and tangential components, both with respect to the orientation of the deformation front and to depth contours of the basement. The two components are accommodated by convergent and strike-slip structures, respectively, which join via a common detachment horizon. The Boomerang Hills Thrust Unit is affected by left-lateral shear as interpreted from the particle displacement field of an unfolded horizon. This shear is invoked by the spatially distributed accommodation of thrust movement along the obliquely striking deformation front. The N 35° thrusting direction of the Boomerang Hills Thrust Unit represents the orthogonal component of strain partitioning caused by the WNW-ESE orientation of the Subandean Zone with respect to a WSW-ENE convergence between the Andes and the Brazilian shield. The tangential component is compensated at the back of the Boomerang Hills Thrust Unit where a positive flower structure is present and strain partitioning is made possible via the detachment horizon. Critical taper analysis shows that thrusting on the south-dipping basement is possible without any substantial internal deformation due to the wedge shape of the sedimentary prism. Therefore, the most important factor controlling the localization of the deformation front is the loss of critical taper at a pronounced edge along the Paleozoic basin boundary. Secondary reasons for deformation localization are small asperities in/close to the top of the basement, e.g. small folds of the early foredeep evolution. Strain partitioning may also play a major role for the evolution of the eastern border of the Bolivian Orocline and in other curved fold-and-thrust belts as discussed for natural and experimental examples. Generally, orthogonal accreting segments evolve faster than obliquely orientated segments due to strain partitioning at the deformation front, hence leading to an increase in the curvature of the belt. Strain partitioning itself is caused by the orientation of the deformation front with respect to the shortening direction. Thus, factors controlling the localization of the deformation front, i.e. paleogeographic features, dominantly control the evolution of curved fold-and-thrust belts. For the eastern flank of the Bolivian Orocline it is postulated that an early Paleozoic rift basin exerts paleogeographic control on Andean deformation, leading to the WNW-ESE orientation of the Subandean Zone between the Chapare and Santa Cruz. Based on map interpretation it is suggested that (a) the previously assumed style of deformation using main thrusts is questionable for this segment of the Andes and (b) deformation involving basally accreting foredeep sediments has to be taken into account. Previously assumed estimates of shortening for the Chapare area in the northern limb of the Bolivian Orocline may therefore be significantly low.