Domenico Montanari

Analogue benchmarks of shortening and extension experiments

Abstract We report a direct comparison of scaled analogue experiments to test the reproducibility of model results among ten different experimental modelling laboratories. We present results for two experiments: a brittle thrust wedge experiment and a brittleviscous extension experiment. The experimental set-up, the model construction technique, the viscous material and the base and wall properties were prescribed. However, each laboratory used its own frictional analogue material and experimental apparatus. Comparison of results for the shortening experiment highlights large differences in model evolution that may have resulted from (1) differences in boundary conditions (indenter or basal-pull models), (2) differences in model widths, (3) location of observation (for example, sidewall versus centre of model), (4) material properties, (5) base and sidewall frictional properties, and (6) differences in set-up technique of individual experimenters. Six laboratories carried out the shortening experiment with a mobile wall. The overall evolution of their models is broadly similar, with the development of a thrust wedge characterized by forward thrust propagation and by back thrusting. However, significant variations are observed in spacing between thrusts, their dip angles, number of forward thrusts and back thrusts, and surface slopes. The structural evolution of the brittle-viscious extension experiments is similar to a high degree. Faulting initiates in the brittle layers above the viscous layer in close vicinity to the basal velocity discontinuity. Measurements of fault dip angles and fault spacing vary among laboratories. Comparison of experimental results indicates an encouraging overall agreement in model evolution, but also highlights important variations in the geometry and evolution of the resulting structures that may be induced by differences in modelling materials, model dimensions, experimental set-ups and observation location.

Granite magma migration and emplacement along thrusts

This paper investigates the influence exerted by brittle tectonic structures in the emplacement of granite plutons in contractional settings. We address both cases where contractional tectonics and magma intrusion are (1) coeval, to study how active contractional tectonics controls the transport of magma, and (2) diachronous, to study the role of pre-existing structures on the transport of magma. In light of new experimental models, we show that magma can rise along thrusts ramps and flats. This phenomenon occurs for both low-viscosity magma (basalts to andesite) and high-viscosity magma (dry granite). The experimental results also allow the evaluation of the role played by magma viscosity in determining pluton geometries. In addition, a review of literature demonstrates a spatial and causal relationship between granites and thrusts and highlights the geometric control of magma pathways in the pluton final shape. The abundance of subhorizontal and tabular granitic intrusions indicates that the location of inflating granitic sills along thrust flats can be common. We argue that active and pre-existing flats-and-ramps thrusts provide a preferential continuous planar anisotropy susceptible to become a granitic magma migration pathway.

Contour map of the top of the regional geothermal reservoir of Sicily (Italy)

An integrated review of existing geological and geophysical data – partly acquired during oil and gas exploration – combined with new data provided by deep geothermal studies of selected key areas, was used for the 3D modeling and mapping of the top of the geothermal reservoir developed at a regional scale in Sicily (Central Mediterranean). The resulting 1:500,000 scale map covers the area of the whole Sicily (about 25,700 km2) and is devoted to represent the main input for both the thermal modeling and the evaluation of geothermal potential at a regional scale. As the map indicates the distribution at depth of a likely target for geothermal drilling, it can be also used as a rough indicator of expected drilling cost for geothermal projects. Such a map can be seen as a useful planning tool for any geothermal project, and related exploration to be carried out in the Sicily region in the future.

Surface-subsurface structural architecture and groundwater flow of the Equi Terme hydrothermal area, northern Tuscany Italy

A multidisciplinary integrated approach was used to study the structural architecture influencing the circulation pattern of geother -mal fluids in the Equi Terme area (NW Alpi Apuane, Tuscany). Geological-structural surveys were carried out to define the structural setting of the area and to characterize geometries and kinematics of fault systems. Chemical (major components) and isotopic analyses (δ18O‰, δ2H‰, 3H, δ13C‰[DIC], δ34S‰[SO4]) were performed on thermal water and cold springs. A geophysical survey was also conducted by means of both Magnetotelluric and Electrical Resistivity Tomography methodologies, in order to gain insight into the resistivity distribution at depth and to indirectly image the subsurface structure. This multidisciplinary approach proved to be a powerful tool, since it unravels the complexity of this natural geothermal system and provides useful suggestion for reconstructing the fluid circulation outflowing at the Equi Terme thermal spring. Results pointed out how the E-W oriented fault system (the Equi Terme Fault) play a key role in controlling the thermal groundwater outflow, and the chemical-physical features of this resource. This structural lineament separates high permeability carbonate complexes (footwall), in which both shallow and deep flow paths develop, from a medium-low permeability succession (hangingwall) that contains evaporitic formations from which thermal water acquires a high salinity and a composition of the Na-Cl (Ca-SO4) type. During the uprising along the fault system, the thermal water is also affected by a mixing with shallow fresh-cold waters that lead to a strong seasonal variation in the chemical-physical properties of the thermal springs.

The Use of Empirical Methods for Testing Granular Materials in Analogue Modelling

The behaviour of a granular material is mainly dependent on its frictional properties, angle of internal friction, and cohesion, which, together with material density, are the key factors to be considered during the scaling procedure of analogue models. The frictional properties of a granular material are usually investigated by means of technical instruments such as a Hubbert-type apparatus and ring shear testers, which allow for investigating the response of the tested material to a wide range of applied stresses. Here we explore the possibility to determine material properties by means of different empirical methods applied to mixtures of quartz and K-feldspar sand. Empirical methods exhibit the great advantage of measuring the properties of a certain analogue material under the experimental conditions, which are strongly sensitive to the handling techniques. Finally, the results obtained from the empirical methods have been compared with ring shear tests carried out on the same materials, which show a satisfactory agreement with those determined empirically.

Shallow Geothermal Exploration by Means of SkyTEM Electrical Resistivity Data: An Application in Sicily (Italy)

A novel procedure for estimating the geothermal energy exchanged by a unit volume was tested in northern Sicily (Italy), where public well data for depicting the complex geological setting were insufficient. An airborne electromagnetic survey was carried out in 2011, providing a 3D cell distribution of resistivity values. The integrated analysis of geological and resistivity data was used to identify six Litho-Electrical Units and to build a 3D geological model. This model was integrated with laboratory thermal conductivity measurements on rock samples, and was used to characterize the heat exchange at depths of up to 200 m, which in turn can be exploited for planning and designing geothermal heating and cooling plants using GSHP (Ground Source Heat Pump).

From obduction to continental collision: New data from Central Greece

The aim of this paper is to contribute to deciphering the evolutionary history of the Hellenides by the study of a large sector of the chain located between the front of the ophiolitic units and the external zones classically attributed to the continental margin of Adria. In particular, the tectonic units located in Boeotia – a key area located in Central Greece at the boundary between the Internal and External Hellenides – were studied from structural, stratigraphic and biostratigraphic points of view. Addressing the main debated aspects concerning the origin of the ophiolite nappe(s), the tectonic evolution of the Hellenic orogen was revised with a particular emphasis on the period between obduction and continental collision. New findings were compared with consolidated data concerning the main metamorphic events recorded in the more Internal Hellenides, geochemistry and age of the ophiolites and main stratigraphic constraints obtained in other sectors of the belt. Finally, a new reconstruction of the tectonic evolution of this area was introduced and, in the context of the dispute concerning the origin of the ‘ophiolitic belts’ as a possible record of multiple oceanic basins, we put forward for consideration a ‘single ocean’ tectonic model spanning from Triassic up to Tertiary times, and valid for the whole Hellenic–Albanian sector.

Geotechnics Shallow and Detailed: Is AEM Up for the Challenge?

Applied Geophysics to Engineering, Geotechnics and Environment is generally synonymous of shallow target, but, at the same time, it demands a detailed reconstruction of the subsurface. The question is:”Is the Airborne EM ready to accept this challenge ?”. Our answer is positive, based on experiences of some case studies, dealing with landslides, shallow geological investigation and so on. Indeed the applications of AEM to geotechnical issues are very few: Beard and Lutro [1] showed the case of an airborne prospect, by using not only EM, but also magnetic, radiometric and VLF data, for the planning of a railroad in Norway; Pfaffhuber et al. [2] used the AEM for the study of rock slides and tunnelling hazards in Norway again; several are the application of the method for environmental purposes, such as potential hazards at coal-waste impoundments [3] or waste site characterization [4, 5, 6, 7]. Other rare applications are focused on the supply of sands and gravels for engineering purposes [8], while the detection of lithologic distributions in alluvial aquifer, due to hydrogeological purposes, is more frequent [9, 10,11].