Does gravity modelling justify a rifted "Ligurian Basin"?

The geo-historical development of the Ligurian Basin and the structure of the crust and upper mantle in this area are still being discussed. Yet it remains unclear if rifting caused continental break-up and seafloor spreading and one of the key questions is whether rifting can be identified in geophysical measurements. For our investigations we had the following updated data sets at our disposal: the new gravity maps of the AlpArray Gravity Working Group (complete Bouguer - CBA, Free air, and isostatic anomalies) the seismic results of the Lobster campaigns of our GEOMAR partners in the SPP MB4D as well as the dynamic modelling results from our own subproject. The constraining data are supplemented with seismic profile data from French and Italian offshore campaigns, as far as they are usable in publications for us. The GFZ modelling software IGMAS+ was used for an interactive 3D modelling. The resulting model contains density inhomogeneities in the crust as well as in the upper mantle down to a depth of 300 km following the results of dynamic models of our own subproject. Due to the special hybrid modelling of the crust (by polygonal structures) and the upper mantle (by voxels of recent velocity models), the individual contributions to the gravity field are clearly separable. As a further special feature, we point out that the density model used is based on the gravity modelling from the first phase of the SPP MB4D (our former subproject INTEGRATE). Thus, a largely consistent 3D density model for both the Alps and the Ligurian Sea is available for interpretation. The constrained 3D modelling of the gravity field, as well as numerical analyses of the fields (terracing, clustering, filtering, curvature), calculations of the vertical stress and Gravity Potential Energy (GPE) suggest that a rift structure in the area of the Ligurian Sea can be identified and mapped. The interactive modelling is supported by the use of geological maps in the Ligurian Sea area. By overlaying the model gravity maps and the geological maps, the good agreement becomes visible – refer to the attached figure

Controls of the Lithospheric Thermal Field of an OceanContinent Subduction Zone: The Southern Central Andes

In an ocean-continent subduction zone, the assessment of the lithospheric thermal state is essential to determine the controls of the deformation within the upper plate and the dip angle of the subducting lithosphere. In this study, we evaluate the degree of influence of both the configuration of the upper plate (i.e., thickness and composition of the rock units) and variations of the subduction angle on the lithospheric thermal field of the southern Central Andes (29°–39°S). Here, the subduction angle increases from subhorizontal (5°) north of 33°S to steep (~30°) in the south. We derived the 3D temperature and heat flow distribution of the lithosphere in the southern Central Andes considering conversion of S wave tomography to temperatures together with steady-state conductive thermal modeling. We found that the orogen is overall warmer than the forearc and the foreland and that the lithosphere of the northern part of the foreland appears colder than its southern counterpart. Sedimentary blanketing and the thickness of the radiogenic crust exert the main control on the shallow thermal field (50 km, the temperatures of the overriding plate are mainly controlled by the mantle heat input and the subduction angle. The thermal field of the upper plate likely preserves the flat subduction angle and influences the spatial distribution of shortening.Fil: Rodriguez Piceda, Constanza. German Research Centre for Geosciences; AlemaniaFil: Scheck Wenderoth, Magdalena. German Research Centre for Geosciences; AlemaniaFil: Bott, Judith. German Research Centre for Geosciences; AlemaniaFil: Gómez Dacal, María Laura. German Research Centre for Geosciences; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Cacace, M.. German Research Centre for Geosciences; AlemaniaFil: Pons, Michaël. German Research Centre for Geosciences; AlemaniaFil: Prezzi, Claudia Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Strecker, Manfred. German Research Centre for Geosciences; Alemani

Variability of the geothermal gradient across two differently aged magma-rich continental rifted margins of the Atlantic Ocean: the Southwest African and the Norwegian margins

The aim of this study is to investigate the shallow thermal field differences for two differently aged passive continental margins by analyzing regional variations in geothermal gradient and exploring the controlling factors for these variations. Hence, we analyzed two previously published 3-D conductive and lithospheric-scale thermal models of the Southwest African and the Norwegian passive margins. These 3-D models differentiate various sedimentary, crustal, and mantle units and integrate different geophysical data such as seismic observations and the gravity field. We extracted the temperature–depth distributions in 1 km intervals down to 6 km below the upper thermal boundary condition. The geothermal gradient was then calculated for these intervals between the upper thermal boundary condition and the respective depth levels (1, 2, 3, 4, 5, and 6 km below the upper thermal boundary condition). According to our results, the geothermal gradient decreases with increasing depth and shows varying lateral trends and values for these two different margins. We compare the 3-D geological structural models and the geothermal gradient variations for both thermal models and show how radiogenic heat production, sediment insulating effect, and thermal lithosphere–asthenosphere boundary (LAB) depth influence the shallow thermal field pattern. The results indicate an ongoing process of oceanic mantle cooling at the young Norwegian margin compared with the old SW African passive margin that seems to be thermally equilibrated in the present day

3-D Simulations of Groundwater Utilization in an Urban Catchment of Berlin, Germany

The objective of this study is to analyze the influence of groundwater pumping on predicted groundwater circulation below the urban center of Berlin, Germany, by 3-D numerical models. Of particular interest are hydraulic head distributions, the related shallow-deep groundwater interactions and their scale dependency within an anthropogenically overprinted environment. For this purpose, two model scenarios are investigated. In the first model realization (Model 1), the effects of groundwater pumping are implemented by imposing a fixed, though spatially variable, hydraulic head distribution over the whole model area, therefore implicitly taking into account the effects of pumping activities. In the second model realization (Model 2), these effects are considered in an explicit manner by imposing variable production rates in locations where pumping activities are ongoing.The results of this study show, that both models predict similar hydraulic head distributions on the regional scale (i.e. urban wide). Locally, differences in the extent, volume and depth of emerging depression cones can be observed. This is manifested in differences in predicted fluid flow patterns supporting or refuting the possibility of contaminant transport in an area of importance for groundwater production (Lower Havel). Herein, the second model approach outlines the necessity of implementing wells as an active parameter to reproduce observed fluid pathways.</p