In orogenic belts high pressure-low temperature (HP-LT) metamorphism can widely affect units derived from both the oceanic and the continental lithosphere. In order to verify whether high P/T (pressure/temperature) ratios recorded in the continental lithosphere can result from tectonic erosion, ablative subduction and recycling in the mantle wedge, we implemented a 2D numerical model to simulate oceanic subduction beneath a continent. Particular attention is paid to the role played by mantle hydration within the continental crust recycled in the wedge region. A comparison between hydrated and non-hydrated models highlights that hydration is fundamental in allowing the recycling of crustal material at shallow depths ( 150 km for a convergence rate of 1 cm year 21 ), making the uprising and exhumation of buried crustal material during active subduction possible. The recycled crustal material can originate from any crustal level. The T max and P max distributions within the final marker configuration show that crustal recycling induces the coupling of volumes that reached different depths during their paths in the corner flow. To verify the reliability of this model we compare predictions with natural geological data from the Austroalpine Sesia-Lanzo Zone (SLZ), the largest eclogite-facies crustal fragment of early Alpine age and whose Alpine tectonic evolution has been interpreted as compatible with a cycle of burial at depth and exhumation during active subduction of the oceanic lithosphere. The relationships between natural P-T estimates and predicted P-T values show that the simulated geodynamic scenario generates a thermal regime coherent with that affecting the subducted continental crust of the SLZ, which may have been stable for a long time during Alpine subduction, allowing the SLZ rocks to accomplish their burial and exhumation path under an active subduction regime.

Abstract. Natural fracture network characteristics can be establishes from high-resolution outcrop images acquired from drone and photogrammetry. Such images might also be good analogues of subsurface naturally fractured reservoirs and can be used to make predictions of the fracture geometry and efficiency at depth. However, even when supplementing fractured reservoir models with outcrop data, gaps will remain in the model and fracture network extrapolation methods are required. In this paper we used fracture networks interpreted from two outcrops from the Apodi area, Brazil, to present a revised and innovative method of fracture network geometry prediction using the multiple-point statistics (MPS) method. The MPS method presented in this article uses a series of small synthetic training images (TIs) representing the geological variability of fracture parameters observed locally in the field. The TIs contain the statistical characteristics of the network (i.e. orientation, spacing, length/height and topology) and allow for the representation of a complex arrangement of fracture networks. These images are flexible, as they can be simply sketched by the user. We proposed to simultaneously use a set of training images in specific elementary zones of the Apodi outcrops in order to best replicate the non-stationarity of the reference network. A sensitivity analysis was conducted to emphasise the influence of the conditioning data, the simulation parameters and the training images used. Fracture density computations were performed on selected realisations and compared to the reference outcrop fracture interpretation to qualitatively evaluate the accuracy of our simulations. The method proposed here is adaptable in terms of training images and probability maps to ensure that the geological complexity in the simulation process is accounted for. It can be used on any type of rock containing natural fractures in any kind of tectonic context. This workflow can also be applied to the subsurface to predict the fracture arrangement and fluid flow efficiency in water, geothermal or hydrocarbon fractured reservoirs.

The structural framework of the Val d’Agri region results from the superposition of different deformation events over time. In this area, the largest European onshore oil field was discovered in the 1980s, and since then, much geologic and geophysical data have been collected. However, the structural complexity and the poor quality of subsurface data have prevented a full understanding of fault evolution and kinematics so far. In this study, scaled sandbox analogue models have been used to better understand the role of syn-rift inheritance in the present-day structural architecture and to test different possible mechanisms of interaction between inherited transpressional structures at depth and newly formed extensional fault systems at shallow levels during regional quaternary extensional tectonics. Analogue models included two consecutive sinistral transpressional phases deforming the basement and the overlying Apulian Platform carbonates, affected by preexisting northeast–southwest-oriented extensional fault zones. The third phase of the experiments consisted of extensional reactivation of the previously formed transpressional structures. Different kinematic solutions were used to investigate the causal relationships between deep and shallow deformation structures. The very good similarity between the experimental results and the natural prototype strongly supports the presence at depth of a main northeast–southwest-oriented syn-rift extensional fault zone, which was affected by positive inversion during the transpressional deformation of the Apulian Platform below the Val d’Agri area. Comparison of experimental results with fault patterns interpreted on available seismic lines indicates that, despite that no direct connection from deep to shallow faults has been recognized, some structural control of the fault pattern at depth on the evolution of the Val d’Agri quaternary extensional fault systems at shallow depth is possible. Extensional deformations at depth can be accommodated by newly formed faults or by the extensional reactivation of inherited high-angle transpressional fault zones.

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