Gerold Zeilinger

The eastern foothills of the Eastern Cordillera of Colombia: An example of multiple factors controlling structural styles and active tectonics

We decipher the geometry, timing, and kinematics of deformation of a region in the eastern foothills of the Eastern Cordillera of Colombia. We assess the influence of inherited structural fabrics, changes in basin geometry, erosional denudation, and the characteristics of the tectonic stress field with respect to the evolution of the structural styles of the deformation front in the Eastern Cordillera. Detailed structural and geomorphic mapping of an area of ∼5000 km 2 , analysis of seismic-reflection profiles, cross-section balancing, tectonic stress-field indicators, and new apatite fission-track data are used to characterize the partitioning of Late Cenozoic deformation in the eastern foothills of the Eastern Cordillera of Colombia. During the late Miocene–Pliocene, in the Eastern Cordillera, deformation migrated from inverted master normal faults to low-elevation, low-amplitude structures in the foreland. However, this shift in the locus of deformation was not spatially uniform. The deformation front is wider in a northern sector of the Cordilleran foothills, where sedimentary units are thicker, and shortening is perpendicular to the structures. This shortening direction is identical to the direction of the greatest horizontal stress S Hmax as seen in borehole breakouts. During the late Miocene–Pliocene, basement ranges are passively uplifted by younger, more frontal thrusts. The eastern foothills of the Eastern Cordillera thus reveal a complex combination of factors responsible for the structural styles and partitioning of active deformation in an inversion orogen. Over time, the most important factor changes, from the role of inherited structural fabrics to the geometries of basin fills.

Climatic Forcing on Channel Profiles in the Eastern Cordillera of the Coroico Region, Bolivia

Orographic precipitation has a large impact on channel morphology and rock uplift via a positive feedback to erosion. We show that in the Eastern Cordillera of Bolivia, channel concavities reach their highest values where annual precipitation increases in the downstream direction, exceeding 3000 mm. The steepest channels are upstream of this zone of high concavity, where precipitation rates are <1000 mm yr−1. Channels exhibit graded forms both upstream and downstream of this transient reach. We conclude that the prolonged effect of orographic erosion and related tectonic uplift is the preservation of channels with extreme concavities in the Eastern Cordillera.

Shear strain localization from the upper mantle to the middle crust of the Kohistan Arc (Pakistan)

Abstract Shear structures from mantle to middle crust levels of the Kohistan palaeo-island arc, in Pakistan, are described. Pre-Himalayan ductile shear zones show a wide variety in size and shape, and developed from gabbro subsolidus to amphibolite facies conditions. Their lithological context and geological history give insights into mechanisms that initiate shear strain localization, factors that control stabilization of deformation in shear zones and flow properties at the mantle-crust transition. Shear strain localization began within compositional gradients. Gabbros were more prone to localization into anastomosing patterns than diorites and granites, which show more homogeneous strain. Shear strain localization during cooling led to less numerous but longer and thicker shear zones. Viscous heating within shear zones resulted in melt production and segregation in deformation structures, and seems to have taken part in the plutonic history of the arc. Using Kohistan as an example, we suggest that the plutonic, lower crust of arcs is strongly affected by subhorizontal, synmagmatic shear zones, probably consistent with the bulk flow direction of the subduction zone. These features can obviously be preserved in collision orogens and may be mistaken for structures documenting the continental collision.

Pre-collisional anastomosing shear zones in the Kohistan arc, NW Pakistan

Abstract Ductile strain localization commonly forms a pattern of shear zones anastomosing around lenses of less deformed rock. Initiation and development of anastomosing shear zones are studied through description of the structures and deformation history of plutonic rocks that form the lower crust of the Kohistan arc. Structures and textures developed in these rocks result from primary magmatic to solid state regional strain, overprinted by anastomosing shear zones. The primary strain was mainly acquired during magmatic emplacement at 100-90 Ma. Strain localization took place continuously from magmatic emplacement to solid state deformation during cooling of the plutons and formed three successive sets of shear zones. Set 1 is composed of associated discrete Riedel and thrust shear zones developed above solidus conditions during southwestward thrusting. Continuous deformation from solidus to amphibolite facies conditions between 100 and 83 Ma formed the second set of shear zones. The lower amphibolite facies set 3 shear zones are diffeentiated by larger strains recorded in the thicker mylonitic zones and enlargement of the spacing between shear zones during cooling. The anastomosing pattern of shear zones described here probably represents arc-related deformation during subduction of the Tethys oceanic lithosphere below the Kohistan arc.

High-temperature and pressure seismic properties of a lower crustal prograde shear zone from the Kohistan Arc, Pakistan

Abstract Anastomosing shear zones exposed in the lower crust of the Kohistan palaeoisland arc in Pakistan have parageneses indicating increasing pressure during deformation. Therefore, they represent a rare example of strain localization during crustal thickening. We investigated the seismic properties of a sheared gabbro with constant bulk chemistry across one of these shear zones. The compressional wave velocity was measured at confining pressures of up to 0.5 GPa and temperatures of up to 600 °C. The density, the average Vp (compressional P-wave velocity) and the acoustic impedance at room temperature increase from the undeformed protolith through the strain gradient to the intensely sheared mylonite. The seismic anisotropy is largest for the strain gradient. The Vp dependence of the velocities on temperature is much higher in the mylonite than in the protolith. The acoustic impedance contrast between protolith and mylonite is high enough to generate seismic reflections at low temperatures, but not at high temperatures. This suggests that the seismic reflectivity may also depend on the temperature. Consequently, ductile shear zones can be detected in reflection profiles of crusts with low geothermal gradients, and may be transparent in crusts with high geothermal gradients.

Fault systems and Paleo-stress tensors in the Indus Suture Zone (NW Pakistan)

Abstract Analysis of fault-striations measured in the Kohistan part of the Indus Suture Zone (NW Himalaya, Pakistan) has been carried out to document dynamic evolution during the brittle stage of the collision of India and Asia. Processing of the data with a direct inversion method identified four stress fields which were chronologically ordered from field evidence as SSE–NNW compression, E–W compression, radial extension and SSW–NNE compression. The last corresponds to the present-day stress field defined from seismic activity. The earlier stress fields are related to times during the Miocene, when convergence-related stresses were disturbed by the formation of the nearby Nanga Parbat and Indus syntaxes.

Immersive 3D Geovisualization in Higher Education.

In this study, we investigate how immersive 3D geovisualization can be used in higher education. Based on MacEachren and Kraaks geovisualization cube, we examine the usage of immersive 3D geovisualization and its usefulness in a research-based learning module on flood risk, called GEOSimulator. Results of a survey among participating students reveal benefits, such as better orientation in the study area, higher interactivity with the data, improved discourse among students and enhanced motivation through immersive 3D geovisualization. This suggests that immersive 3D visualization can effectively be used in higher education and that 3D CAVE settings enhance interactive learning between students.

Active tectonics evaluation from geomorphic indices for the central and the southern Longmenshan range on the Eastern Tibetan Plateau, China

We applied the geomorphic indices (hypsometry and stream length gradient) to evaluate the differential uplift of the central and southern Longmenshan, a mountain range characterized by rapid erosion, strong tectonic uplift and devastating seismic hazards. The results of the geomorphic analysis indicate that the Beichuan-Yingxiu fault and the Shuangshi-Dachuan fault act as major tectonic boundaries separating areas experiencing rapid uplift from slow uplift. The results of the geomorphic analysis also suggest that the Beichuan-Yingxiu fault is the most active fault with largest relative uplift rates compared to the rest of the faults in the Longmenshan fault system. We compared reflected relative uplift rates based on the hypsometry and stream length gradient indices with geological/geodetic absolute rates. Along-strike and across-strike variations in the hypsometry and stream length gradient correlate with the spatial patterns derived from the Apatite Fission Track (AFT) exhumation rates, the leveling-derived uplift rate, and co-seismic vertical displacements during the 2008 Wenchuan earthquake. These data defined multiple fault relationships in a complex thrust zone and provided geomorphic evidence to evaluate the potential seismic hazards of the southern Longmenshan range.

Estimating the fill thickness and bedrock topography in intermontane valleys using artificial neural networks

Thick sedimentary fills in intermontane valleys are common in formerly glaciated mountain ranges but difficult to quantify. Yet knowledge of the fill thickness distribution could help to estimate sediment budgets of mountain belts and to decipher the role of stored material in modulating sediment flux from the orogen to the foreland. Here we present a new approach to estimate valley fill thickness and bedrock topography based on the geometric properties of a landscape using artificial neural networks. We test the potential of this approach following a four-tiered procedure. First, experiments with synthetic, idealized landscapes show that increasing variability in surface slopes requires successively more complex network configurations. Second, in experiments with artificially filled natural landscapes, we find that fill volumes can be estimated with an error below 20%. Third, in natural examples with valley fill surfaces that have steeply inclined slopes, such as the Unteraar and the Rhone Glaciers in the Swiss Alps, for example, the average deviation of cross-sectional area between the measured and the modeled valley fill is 26% and 27%, respectively. Finally, application of the method to the Rhone Valley, an overdeepened glacial valley in the Swiss Alps, yields a total estimated sediment volume of 97 ± 11 km3 and an average deviation of cross-sectional area between measurements and model estimates of 21.5%. Our new method allows for rapid assessment of sediment volumes in intermontane valleys while eliminating most of the subjectivity that is typically inherent in other methods where bedrock reconstructions are based on digital elevation models.

DECISion-Support System for Radiological Diagnostic

A software package to develop, maintain and evaluate decision-support systems for radiological diagnostic was devised. The programs, designed as WINDOWS-Applications for PC — versions for other hardware platforms are planned — empower physicians to build and refine consultation systems without the necessity of intervention by software engineers. Applications created with these software tools for particular radiological domains support radiologists at their diagnostic work by offering a question-answer dialog to promote a systematic check of appearance or absence of findings, and by informing about the agreement and/or disagreement of that finding selection with possible diagnoses. Example images of findings and diseases are displayed by request. Consultations can be stored for documentation and/or prospective system verification and improvements. At present, two applications for the radiological fields High Resolution CT of the Lung and MR of the Traumatic Knee were originated.