From Magma to Groundwater: The Brine Connection

Abstract

The heat and mass flow between deep magmatic sources and the base of geothermal systems near the Earths surface is investigated through mathematical models which arise from the concept that hot dense brines at high pressure control the upflows of fluids and chemicals dissolved in them. Recent work on correlations describing the T-p-X state-space for the system over a wide range of temperatures and pressures is used in calculations based on the equations describing the conservation of mass, momentum and energy of the components in systems which are bounded below by magmatic heat and mass sources and above by the base of geothermal reservoirs. The various parts of deep brine-saturated systems which correspond to different regions in the T-p-X state-space are delineated in model examples, showing where gas, liquid and two-phase brine flows may exist as well as regions where solid chloride is either deposited or dissolved. Detailed results in the form of temperature, pressure and chloride mass fraction profiles are derived from simple one-dimensional models of vertical flow regimes. These aid understanding of how hot dense brines interact with groundwater and how they operate as a temperature control mechanism confining molten magma temperatures to the bottom of these systems. They also demonstrate how steep brine concentration gradients may control the long-time mass and heat flows.