Temperature field distribution from cooling of a magma chamber in La Primavera caldera, Jalisco, Mexico

Abstract

The temperature field distribution in La Primavera geothermal area, Jalisco, located in the western part of the Mexican Volcanic Belt (MVB), has been simulated from cooling of a shallow magma chamber (assumed as the primary heat source) during the entire volcanic history of the caldera. Similar to the other two geothermal fields of the MVB (Los Humeros and Los Azufres), it is considered that the evolution of the magma chamber is controlled by the processes of fractional crystallization as well as magma recharge. Besides these processes, heat contribution is also taken into account from decay of natural radioactive elements, U, Th, and K, present in all geological materials. In some models presented in this work, convection in the geothermal reservoir is simulated by assigning higher values of thermal conductivities (up to 20 times the rock conductivities) to respective geologic units. The heat transfer equation has been solved by a finite element implicit method. The results of temperature simulations from the magma chamber are compared with undisturbed formation temperatures in three drill wells. The subsurface depth of the top of the magma chamber is varied from 5 to 7 km. Similarly, the horizontal dimensions of the chamber are varied from 12 km (which is approximately the diameter of the La Primavera caldera) to 10 km. The thermal effects of this change in depth and horizontal dimensions of the magma chamber are readily seen in the predicted temperature distribution for this rather young caldera. (C) 1997 CNR.