Temperature distributions from cooling of a magma chamber in Los Azufres geothermal field, Michoacan, Mexico

Abstract

The temperature distribution in Los Azufres geothermal field, Michoacan, has been modelled assuming a shallow magma chamber at a depth of -5 km. The evolution of the magma chamber is controlled by the processes of magma recharge as well as fractional crystallization, the latter being the dominant petrogenetic process. The heat contribution of these processes is taken into account. The heat transfer equation was solved by a finite difference explicit method. The process of fractional crystallization requires a time interval of -0.1 Ma for the chamber to cool from basalt to rhyolite liquidus temperatures. The corresponding heat contribution amounts to a temperature increase of -410°C. This value is considerably larger than the -300°C estimated for "one-step" cooling. The recharge of the chamber is assumed equivalent to -36 km3 of basaltic magma during the past 0.36 Ma. This was modelled thermally by assuming a recharge rate of 0.1 km3 of magma per 1000 years over 0.36 Ma. Convective processes within the geothermal reservoir were considered at least during the past 0.1 Ma. The processes of fractional crystallization, magma recharge and convection must all be considered for optimal agreement between the simulated and measured temperatures.