Numerical Investigation on Cooling Process of a Magma Chamber in Geothermal System

Suggestion of a Numerical Model and Analysis of Early Cooling Process

Abstract

We numerically investigated early cooling process of a magma chamber in order to construct a comprehensive model of geothermal system, which includes both a deeper heat source and a shallower hydrothermal system. Conservation of mass, momentum, energy, and dissolved and exsolved volatile components were taken into account in 2-D space, emphasizing the role of exsolution process with nucleation and growth of bubbles. The calculation for 182 years considering a granitic magma chamber containing 4wt% of water at a depth of 4km was achieved and showed a stable zone at the upper part of the magma chamber because of exsolution of volatile components, though the calculation time span is too short to discuss the evolution of a geothermal system. The appearance of the stable zone affected not only flow velocity of the magma but also distributions of all parameters. The instability of numerical calculation after 182 years seems to be attributed to the formation of the stable zone. Some improvement of numerical method may be needed. Taking account of values suggested by previous studies, the obtained degassing rate might be possible. However there still are matters to be considered such as crystallization in vicinity of magma-crust boundary or compression by vesiculation.