Abstract The subsurface provides multiple resources, the exploitation of which has a lasting impact on future potential provision. Establishing sustainability in terms of fundamental principles, and fitting these principles into a practical framework, is an ongoing endeavour focused mainly on surface activities. The principles of ecological economics lead to six challenges that summarize the current limitations of implementing science-based sustainable management of geological resources in the medium to deep subsurface: integrating value pluralism, defining sustainable scale, evaluating interferences in the subsurface, guaranteeing environmental justice, optimizing environmental and economic efficiency and handling uncertainties. Assessing and managing geological reservoirs is particularly challenging because of slow resource regeneration, complex spatial and temporal interactions, concealment and naturally dictated opportunities. In answer to the challenges, visions are proposed that outline how an indicator framework is needed for guidance, how indicators require reservoir models with extended spatial and temporal scope, how differences in social values in relation to the environment are to be considered and how real option games combined with life cycle assessment can be used for optimizing efficiency. These individual solutions relate to different facets of the same problem, and can be integrated into one overarching solution that takes the form of dynamic multi-criteria decision analysis.

Abstract Exploration of this geothermal field was begun formally, though intermittently, in 1958; the first exploratory well was drilled in 1959, and official production of the first megawatts began in 1973. The commercial development of Cerro Prieto geothermics began with practically no previous experience. This explains the relatively long period between initial exploration, drilling, and power generation as compared with the development of similar fields in other countries and in Mexico itself. Since 1958, but especially from the mid-sixties to the present, many studies have dealt with the Cerro Prieto geothermal field and its surroundings. The fact that more than 200 papers have been published in Mexico alone precludes even listing them here; foreign publications are at least as numerous, and unpublished reports of the Federal Commission on Electricity easily duplicate that amount as well. Research on the Cerro Prieto field covers virtually all geoscientific disciplines: regional and local geology, structural and tectonic geology, regional and local geohydrology, subsurface geology, sedimentology, volcanology, fission-track dating, hydrothermal alteration, mineralogy, geological modeling, remote sensing, ground compaction and subsidence, determination of petrophysical properties, etc. Geophysical investigations cover resistivity, geophysical well-logging, gravity, reflection and refraction seismology, ground and aerial magnetometry, spontaneous potential, magnetotelluric analysis, microseismics, and precision gravimetry. Geochemical studies utilize geochemistry of surface shows, analysis of well fluids, geochemistry of gases, geothermometry, use of tracers, determination of radon in geothermal fluids, isotopic chemistry in fluids and minerals, and geochemical modeling. Drilling engineering covers types of pipes, cements and high-temperature drilling muds, well-completion techniques, and high

We review the northwest African Cenozoic volcanic fields, including their regional geology. This provides a basis for understanding the relations between Hoggar volcanism and the Africa-Europe collision. Volcanic alignments are related to structural features, and no spatial age trend exists. In Hoggar, a close link is established between the volcanism and Pan-African structure. During the Mesozoic rifting period, the Hoggar area was already a topographic high well before any volcanism, which began at ca. 35 Ma, just after the initiation of the Africa-Europe collision at ca. 38 Ma. Hoggar volcanism continued episodically until now, as did the collision. We describe the Hoggar volcanic province based on available field, petrological, geochemical isotopic, and geophysical data, including data on gravimetry, heatflow, and seismic tomography. The latter suggests that northwestern African volcanism is linked to mantle structure down to 150 km but not deeper, implying a shallow mantle source. In Hoggar, lithospheric structures deduced from the seismic tomographic model and from geology are compatible when their respective resolutions are taken into account. The considerations just stated cannot be reconciled with a plume model. We propose instead that intraplate stress induced by the Africa-Europe collision reactivated the Pan-African mega–shear zones mainly in metacratonic terranes, inducing linear lithospheric delamination, rapid asthenosphere upwelling, and melting due to pressure release. Edge-driven convection may contribute. The surface location of the volcanism is influenced by Paleozoic and Mesozoic brittle faults. Myth: A simplified picture, often illusory, that groups of humans elaborate or accept concerning a person or a fact and which plays a determining role in their behavior or their appreciation. Translated from Dictionnaire Le Robert (1990)