• Energy Research

The Western Tuscany, in the inner sector of the Northern Apennines, is characterized by a thinned con-tinental crust (~20-25 km), high heat flow (>100 mW m-2), and the presence of magmatism. The latterproduces the current geothermal activity, which is mostly localized at the large Larderello-Travale fieldsettled above the granites with the same name. These features and the several Late Miocene sedimen-tary basins that developed in the area are normally related to an extensional tectonics that affected theback-arc area since the Early-Middle Miocene (~16 Ma), although, some geophysical studies image thecontinental crust deformed by W-dipping thrust faults. Here we present a new field survey conductedin the Radicondoli-Volterra Basin, which bounds the Larderello-Travale pluton system to the northeast.The results support former conclusions that the basin infill has been intensely shortened. Integratedanalysis of other surrounding hinterland basins suggests that a phase of regional shortening affected theback-arc area approximately between 7.5 and 3.5 Ma. This period partly overlaps with the emplacementof the Larderello-Travale granites that started no later than 3.8 Ma, thus raising the possibility that com-pressive structures may have - at least in part - controlled magma emplacement, and/or also that theearly emplacement of the Larderello-Travale granites occurred when the compressive stresses startedto decay. In some cases, isotherms localize and elongate in the direction of subsurface anticlines in thebasement, as occurs in the Travale area. Comparison with the results of analogue models indicates thatthe core of active and inactive fold anticlines in the basement may focus the upraising of magmatic fluids,with obvious implications for the geothermal exploration of the area.

Caldera collapse received large attention during the last decades and was widely studied using various approaches, spanning from field-geology to numerical and analogue modelling. Analogue models allow to reproduce caldera collapse deformation, providing information otherwise difficult to obtain during such an extremely transient geological process. A wide range of analogue studies is available in literature, nonetheless, some aspects are still barely known, particularly the propagation of caldera faults and the role of inherited structures during caldera collapse. We have thus addressed the above research questions through analogue models. Our models show how calderas may experience asymmetry due to the lateral propagation of caldera-related faults. Furthermore, inherited discontinuities may affect caldera collapse by inducing rectilinear caldera faults that generate non-circular ring faults. Finally, sub-vertical discontinuities may be able, in specific conditions, to inhibit the formation of standard caldera structures that have been commonly observed in previous experimental series (i.e., early inward-dipping reverse faults followed by peripheral normal ring faults). Our models were then compared with four natural examples (the Acoculco and Los Humeros caldera complexes in Mexico, the Tuscolo-Artemisio caldera in the Colli Albani volcanic district, Italy and the Glencoe Caldera in Scotland), suggesting a relevant control exerted by inherited faults during caldera collapse. On the basis of the modelling results, we propose an evolutionary model that can be generalized and likely applied to many other caldera settings worldwide.

Magma emplacing at shallow crustal levels may cause significant deformation in the overlying country rock (i.e., forced folding, fracturing and faulting), both at a local and/or regional scale. To get insights into these processes, we investigated in the laboratory the development of forced folds and associated fracture/fault networks. An analogue magma, simulated by polyglycerols, was intruded into a sand pack representing the brittle crust. The scaled analogue models reproduced different 3D deformation structures depending on the model parameters (e.g., magma viscosity, injection rate, volumetric flux, and the rheology and thickness of the host and cover rocks). However, all models support the observation that the emplacement of shallow magmatic bodies may result in the growth of dome-shaped forced folds, and associated development of tensional and compressional deformation in the host-rock. Although the models involve simplifications, these results provide useful hints for geothermal research, as fractures and faults associated with magma emplacement can significantly influence the distribution and migration of superhot geothermal fluids. These structures can therefore be considered potential targets for geothermal and/or ore deposit exploration. In this perspective, the results of analogue models may provide useful geometric constraints for field work, numerical modelling, and particularly seismic interpretation, allowing production and a better understanding of integrated conceptual models concerning the circulation of supercritical fluids.

Magma overpressure at the time of the emplacement at shallow crustal levels may lead to deformation (i.e. forced folding, fracturing and faulting) in the country rock, both at local and regional scale. To get insights into this process, we reproduced and analysed in the laboratory the fracture/fault network associated with the emplacement of magma at shallow crustal levels. We used a mixture of quartz sand and K-feldspar fine sand as an analogue for the brittle crust, and polyglycerols for the magma. The models were able to reproduce complex 3D architectures of deformation resulting from magma emplacement, with different deformation patterns -invariably dominated by forced folding and associated brittle faulting/fracturing- resulting from variable parameters. These results provide useful hints into geothermal researches. Fractures and faults associated with magma emplacement are indeed expected to significantly influence the distribution and migration of superhot geothermal fluids near the edge of the magma intrusion. These structures can therefore be considered as potential targets for geothermal or mineral deposits exploration. In this perspective, the results of analogue models may provide useful geometric and conceptual constraints for field work, numerical modeling, and particularly seismic interpretation for achieving a better understanding and tuning of the integrated conceptual model concerning the circulation of supercritical fluids. The research leading to these results has received funding from the European Community's Seventh Framework Programme under grant agreement No. 608553 (Project IMAGE).

AbstractScaled analogue models explored the role of different boundary conditions in intra‐caldera resurgence processes. Models investigated the role of magma intrusion depth (ID) (Series 1), asymmetric and symmetric caldera collapse (Series 2), as well as the presence of existing discontinuities in the pre‐volcanic substratum (Series 3) on the style of caldera resurgence. Experimental results indicate that different IDs resulted in different resurgence styles and structural patterns, which evolved from piston‐like resurgence, for deeper intrusions, to intra‐caldera resurgent domes for shallower intrusions. Asymmetric collapse was typically accompanied by a tilted roof block above the emptied analogue magma reservoir, while inherited faults influenced significantly the deformation pattern of piston‐like resurgence. Experiments simulate many of the principal characteristics of calderas. We compare our modeling results primarily to the Los Potreros caldera nested within the Los Humeros Volcanic Complex, where the largest Mexico's Quaternary eruption occurred and which hosts an important geothermal field (eastern Trans‐Mexican Volcanic Belt). A structural field survey was conducted to identify the kinematics of faults within the caldera and outside the volcanic edifice. The Los Potreros caldera shows a sub‐orthogonal fault pattern strikingly similar to that of models deformed with shallow ID. We interpret this correlation as an evidence of similarity in dynamic processes, whereby modeling results would indicate a scaled ID of ∼4.5 km. The Acoculco caldera complex, in Mexico, shows a fault pattern similar to the Los Potreros caldera, and geological information corroborates the attribution of renewed magmatic pressure to similar IDs.

This dataset presents the results of an experimental series of analogue models performed to investigate caldera resurgence processes, particularly the setting of the Los Potreros caldera that belongs to the Los Humeros Volcanic Complex (Puebla State, Mexico). Our experimental series was designed adopting a parametric approach, which consisted in the systematic variation of controlling parameters, such as: depth of intrusion, overburden thickness above the analogue magma chamber, presence of inherited discontinuities. Structures of models have been analysed quantitatively by means of (i) photogrammetric Digital Elevation Model reconstruction, (ii) semi-automatic fault pattern quantification and (iii) Digital Particle Image Velocimetry techniques. In this dataset, we show the row data and specific elaborations supporting the interpretation of modelling results. {"references": ["Donnadieu, F., Kelfoun, K., de Vries, B. V. W., Cecchi, E., & Merle, O. (2003). Digital photogrammetry as a tool in analogue modelling: applications to volcano instability. Journal of Volcanology and Geothermal Research, 123(1-2), 161-180. https://doi.org/10.1016/S0377-0273(03)00034-9", "Healy, D., Rizzo, R. E., Cornwell, D. G., Farrell, N. J., Watkins, H., Timms, N. E., ... & Smith, M. (2017). FracPaQ: A MATLAB\u2122 toolbox for the quantification of fracture patterns. Journal of Structural Geology, 95, 1-16. https://doi.org/10.1016/j.jsg.2016.12.003", "Thielicke, W. and Stamhuis, E.J., 2014. PIVlab \u2013 Towards User-friendly, Affordable and Accurate Digital Particle Image Velocimetry in MATLAB. Journal of Open Research Software, 2(1), p.e30. DOI: http://doi.org/10.5334/jors.bl"]} This dataset provides supporting information to "Bonini, M., Maestrelli, D., Corti, G., Del Ventisette, C., Moratti, G., Carrasco‐Núñez, G., et al. (2021). Modelling intra‐caldera resurgence settings: Laboratory experiments with application to the Los Humeros Volcanic Complex (Mexico). Journal of Geophysical Research: Solid Earth, 126, e2020JB020438. https://doi.org/10.1029/2020JB020438 " The models and the derived data have been elaborated at the Tectonic Modelling Laboratory of CNR-IGG and University of Florence, Italy.