The study of heat transfer mechanisms in hydrothermal systems is important for understanding the basic physics behind orebody formation and mineralization in the upper crust (Bickle and Mckenzie 1987; Bjorlykke et al. 1988; Brady 1988; England and Thompson 1989; Hoisch 1991; Connolly 1997). Generally, heat energy may be transferred within the crust in the following forms: conduction, advection (including forced convection) where the heat is carried by a moving mass of rock during def- mation or by a moving uid, convection (i. e. , free convection, natural convection, buoyancy driven convection, temperature gradient driven convection) and a com- nation of these processes. Since advective ow is usually generated by a pore- uid pressure gradient, heat transfer due to advective ow is largely dependent on the pore- uid pressure gradient distribution in hydrothermal systems. A typical ex- ple of this advective ow is the upward through ow caused by lithostatic pore- uid pressure gradients within the lower crust. Extensive studies (Connolly and Ko 1995; Etheridge et al. 1983; England et al. 1987; Fyfe et al.
1978; Walther and Orville 1982; Peacock 1989; Yardley and Bottrell 1992; Hanson 1992; Yardley and Lloyd 1995; Norton and Knapp 1970) have shown that lithostatic pore- uid pressure can be built up by metamorphic uids arising from devolatilization and dehydration - actions, if the permeability is low enough to control uid ow in the lower crust.