Hierarchy System of Geothermal Structures--A New Outlook on Generation and Transport of Geothermal Energy in Modern Volcanic Areas

Abstract

It is demonstrated that geothermal resources of modern volcanic areas are distinctly confined to the hierarchic system of geological structures: geothermal provinces – geothermal districts – hydrothermal-magmatic systems – geothermal reservoirs (deposits). Geothermal provinces are geological structures of graben-syncline types which control regional conductive and convective heat flows. Geothermal districts are identified with long-existing volcanogenic ore centers (centers of endogenic activity) that appear on the surface as oval-circular megastructures with a diameter of 18-24 to more than 40 km. Hydrothermal-magmatic systems are crustal permeable axisymmetrical geologic structures of the type of large volcanic-tectonic structures up to more than 18-24 km in plan and forming a distinctive self-insulated convection cell (Geothermal …, 2005). Geothermal reservoirs (deposits) are not only geological-economic conception, but also represent a system of joint upstanding and downthrown tectonic blocks with a thickness of up to n x 100 m, which control local flows of ascending fluids and descending meteoric (mixed) waters. Geothermal deposits, as a rule, are located in the central parts of hydrothermal-magmatic systems, which is determined by the position of a heat (fluid) source. The paper addresses the geological setting of geothermal provinces–districts–systems– deposits, heat (ore – fluid) feed sources, hydrothermal metamorphism of rocks, dynamics of gas-liquid and water flows, a role of gases in geology of hydrothermal-magmatic systems and in heat transport, possible heat energy storage and transfer mechanisms, etc. A model for hierarchy system of geothermal structures is suggested (from regional to local) to be built upon when applying a geological approach to assessment of prospective energy and mineral resources of modern volcanic areas.