Role of lithospheric-scale geological heterogeneity in continental lithosphere dynamics

Starting from our analysis of the Alpine orogen in 4D-MB (Spooner et al. 2022), we analysed how the Alps compare to other parts of the Alpine-Himalayan collision zone (AHCZ). We find that all orogens in the AHCZ exhibit characteristic diffused seismicity compared to the intraplate regions (Storchak et al. 2013). Interestingly, they also show a thicker-than-average silica-rich upper crust and total crustal thickness, while their lithosphere thickness has been shown to be similar to that of stable continental interiors (e.g., Tibet, Zagros Priestley et al. 2018). These observations provide a metric for the lithospheric-scale geological inheritance, the role of which we aim to understand in continental lithosphere dynamics over geologic timescales. We use data-driven modelling to compute the present-day thermomechanical state of the AHCZ lithosphere (Cacace & Scheck-Wenderoth 2016). To do so, we first compute 3D steady-state temperature distribution in the AHCZ considering variations in the crustal layers from published models with representative radiogenic heat production and thermal properties. The temperature boundary condition is fixed at the surface to 15oC and at the base of the model (200 km) is derived from the conversion of seismic tomography models. We then compute the differential stress distribution for the AHCZ using equilibrium 3D temperature distribution and laboratory-derived rheological properties representative for each layer in the model. Our results (Kumar et al. 2023) indicate the existence of a critical crustal thickness, which is thermodynamically controlled by the internal energy and chemical composition of the crust. The value of this critical crustal thickness matches the global average of continental crust thickness. Orogenic lithospheres with thicknesses above this critical value possess higher potential energy and are weakened by the internal energy from heat-producing elements, whereas continental intraplate regions with thicknesses close to the critical crustal thickness are stronger. Weaker orogenic lithospheres deform via dissipating this energy in a diffused deformation mode, leading to zones of deformation in contrast to focused deformation at the plate boundaries. The observed crustal differentiation in the AHCZ could be understood as perturbations to the critical crustal thickness caused by plate-boundary forces. The dynamic evolution of these perturbations (Houseman & Houseman 2010) indicates that the critical crustal thickness is a stable fixed-point attractor in the evolutionary phase space of the continental lithosphere. The exact characteristics of the evolutionary path depend on the amplitude of perturbations, the source of the initial driving energy, and the relaxation time scale of the active dissipative process (thermal diffusion and/or viscous deformation). Typical ranges of thermal properties and viscosities of the continental lithosphere suggest that the thermal diffusion always lags the viscous relaxation giving rise to a thermodynamic feedback loop between thermal and mechanical relaxation of the out-of-balance energy in the orogenic lithosphere. Exponentially growing energy states, leading to runaway extension are efficiently dampened by enhanced dissipation from radioactive heat sources. This eventually drives orogens with their thickened radiogenic crust towards a final equilibrium state

Research on Utilization of Geo-energy

AbstractThe world's energy demand will increase year by year and we have to search for alternative energy resources. New concepts concerning the energy production from geo-resources have to be provided and developed. The joint project GeoEn combines research on the four core themes Geothermal Energy, Shale Gas, CO2 Capture and Utilization and CO2 Storage. The research is carried out in the federal state Brandenburg in Germany where all project partners - Helmholtz Centre Potsdam, University of Potsdam, Brandenburg University of Technology - and the infrastructures - Schwarze Pumpe, Ketzin, Groß Schönebeck - are located

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Large-scale diapiric salt movements affect the architecture of sedimentary basins and often prevent the understanding of their mechanics by hiding or distorting subsidence patterns. One good example is the evolution of the Transylvanian Basin, which formed during Miocene times in an area located in between the rapid slab rollback and continental collision recorded at the exterior of the Carpathians and the extension of the neighbouring Pannonian Basin. In the absence of major genetic fault systems, quantifying these external tectonic forcing factors requires an accurate reconstruction of subsidence evolution. Having the advent of a detailed 3D geometrical model of the Transylvanian Basin, we apply a 3D numerical modelling technique that couples salt re-distribution and subsidence evolution to quantify and understand the basin kinematics and vertical motions. Two techniques, backward and forward modelling are coupled in order to discriminate between salt migration driven by overburden and the influence of external tectonic forcing factors. The results show that salt kinematics was more complex than simple unidirectional migration, suggesting the existence of areas with significant subsidence hidden by the inward salt migration and areas with apparent large subsidence that are in reality artefacts of outwards salt migration. Additionally, the results suggest that parts of the basin have been successively affected by in- and out-ward salt migration events, an effect of localising subsidence and overburden. Furthermore, accelerated moments of salt migration took place during the main Miocene contraction events recorded at the exterior of the Carpathians, demonstrating that salt migration is enhanced by intraplate stresses. Our study also infers that the subsidence of the Transylvanian Basin is the result of the superposition of the contraction at the exterior of the orogenic chain and the back-arc extension

Beckenmodellierung : Temperatur in Sedimentbecken

The formation of mineral and energy resources involves the interaction of groundwater flow, mechanical deformation, mass and heat transport processes. Thereby, groundwater flow patterns, temperature field, and fluid-rock interactions are all interdependent. This calls for a unified description linking the coupling between the different scales and related physical phenomena involved. A mathematical formulation of the main driving processes affecting basin fluid and heat transport allows developing numerical models as tools to examine the interactions of simultaneously active processes and variable parameters within the constraints given by physical principles and taking into account proper temporal and three dimensional spatial scales. Therefore, the usage of mathematical models is justified by the help they bring in the understanding and verification of specific mechanisms acting in natural systems. In Section “Basin Analysis” at GFZ German Research Centre for Geosciences mathematical models of increasing degree of complexity are applied to the study of energy and mass transport processes in complex sedimentary basins

Rekonstruktion der Absenkungsgeschichte des Argentinischen Kontinentalrands

Sedimentary basins represent geological archives. Accordingly, 3D basin models that integrate geological and geophysical observations can be used to reproduce not only their present-day structural configuration and distribution of physical properties, but also their evolution including the subsidence history. For example, the thickness of deposited sediments reflects the amount of subsidence caused by the sediment load. The corresponding load-dependent vertical movements (called isostatic subsidence) can be sequentially subtracted from the total subsidence in order to reconstruct past depth configurations. Another aspect of basin subsidence is caused by thermal processes that can also be approximated by studying the present-day basin configuration. If the basin formation is related to lithospheric stretching and thinning, it initially involves a thermal disturbance due to which the geothermal gradient is increased by an amount depending on the observed strain. After stretching has ceased, the lithosphere starts cooling down and approaches a thermal equilibrium. This cooling process is accompanied by an increase in rock density and related thermal subsidence, which can also be assessed. By calculating the two subsidence components for certain stratigraphic intervals, the corresponding temporal changes in water depths (paleobathymetries) can be reconstructed for our understanding of subsidence dynamics. This research methodology was applied to the conjugate passive continental margins of Africa and Argentina in order to analyse and compare the evolution of sedimentary basins after the formation of the South Atlantic. This study mainly focussed on the Argentinian Colorado Basin because of its complex evolution and economic resource potential

Modelling the Surface Heat Flow Distribution in the Area of Brandenburg (Northern Germany)

A lithosphere scale geological model has been used to determine the surface heat flow component due to conductive heat transport for the area of Brandenburg. The modelling results have been constrained by a direct comparison with available heat flow measurements. The calculated heat flow captures the regional trend in the surface heat flow distribution which can be related to existing thermal conductivity variations between the different sedimentary units. An additional advective component due to topography induced regional flow and focused flow within major fault zones should be considered to explain the spatial variation observed in the surface heat flow

Lithospheric 3D gravity modelling using upper-mantle density constraints: Towards a characterization of the crustal configuration in the North Patagonian Massif area, Argentina

The North Patagonian Massif is an Argentinean plateau that has an average height of 1200 m and stands from 500 to 700 m above the neighboring areas. During Paleogene, it suffered a sudden uplift of more than 1200 m without noticeable internal deformation; thus, it could be related to isostatic disequilibrium. To shed light on the geodynamic development of the area it is necessary to characterize the present-day configuration of the crust. In this study, a lithospheric-scale 3D density model was developed by integrating all the available data of the area with the objective of assessing the depth of the crust–mantle discontinuity (Moho). During the construction of the initial density model, we tested different mantle density scenarios obtained using P- and S-wave velocities from tomographic models, converting them into densities and comparing the conversions with densities obtained from xenoliths. Below the North Patagonian Massif plateau, we have derived a Moho depth between 40 and 50 km which is from 2 to 7 km deeper than its surroundings. There is an evident correlation between high topography and deep Moho that would indicate isostatic equilibrium at present. The model results provide a new approach to the Moho depth in an area where there is no seismic constraining information about this discontinuity. In addition, we found a spatial correlation between the variation of the mean crustal density and the location of the Paleozoic terranes that were proposed to constitute the basement of Argentina.Fil: Gómez Dacal, María Laura. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Departamento de Gravimetría; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Tocho, Claudia. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Departamento de Gravimetría; Argentina. Comisión de Investigaciones Científicas de la Provincia de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Aragon, Eugenio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; ArgentinaFil: Sippel, Judith. Universitat Potsdam; AlemaniaFil: Scheck Wenderoth, Magdalena. German Research Centre for Geosciences; AlemaniaFil: Ponce, Alexis Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Ciencias de la Tierra y Ambientales de La Pampa. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales. Instituto de Ciencias de la Tierra y Ambientales de La Pampa; Argentin

INTEGRATE - Integrated 3D structural, thermal, gravity and rheological modeling of the Alps and their forelands

The aim of this project was to obtain a better understanding of the crust and the uppermost mantle beneath the Alpine orogen and its forelands and to test different hypotheses on the configuration of the subduction system as well as on the distribution of deformation and seismicity. Therefore, we have integrated the geoscientific observations publicly available so far on properties of the sediments and the crystalline crust (geometry, seismic velocities, and densities) with seismologically derived heterogeneities in the sub-crustal mantle into a consistent data-based 3D structural model that resolves the first-order contrasts in physical properties of the units composing the orogen and the forelands. The derived structural model was additionally constrained by 3D gravity modelling and used as input to derive a lithospheric temperature field based on petrological assumptions on the composition of the crust and mantle. This is done to study the effects of regional heat-flow into the Alps and their foreland basins. Starting from these 3D density thermal and lithology models, the integrated strength was derived and discussed in the context of stress and deformation fields. The project led to the successful completion of a dissertation by Cameron Spooner who obtained the highest possible grade (“summa cum laude”) from the University of Potsdam and published 4 high-level papers. Also, a Master thesis was successfully completed by Max Lowe at CAU Kiel that also led to a publication (Lowe et al. 2021). As members of the AAAGRG, the partners of CAU Kiel were significantly involved in the compilation of the new gravity maps for the Alps and their forelands (Zahorek 2021). The project contributed to “Theme 3: deformation of the crust and mantle during mountain building”, in providing the configuration of the different crustal units and of the lithospheric mantle. The project also contributed to “Theme 4: motion patterns and seismicity” in that it supported identifying spatial patterns of faulting and seismicity in relation to the rheological configuration. In response to its regional character, the project links with the different activity fields of the SPP and a continuous exchange of observations and modelling results with many working groups in the SPP and supported data processing and interpretation