长英质岩浆中不混溶流体的运移机理──兼论成矿作用发生的条件

MIGRATING MECHANISM OF IMMISCIBLE FLUID IN FELSIC MAGMATIC SYSTEM

与岩浆作用有关的热液矿床的形成，在一定程度上是岩浆体系内富含挥发分流体的组成、压力及性质演变的结果。长英质岩浆中无水硅酸盐矿物的结晶导致挥发性组分以气泡形式存在。气泡的体积随岩浆演化程度增强而不断增大，由于两不混溶流体之密度差而产生的力的作用使气泡相对硅酸盐熔体（＋晶体）超前向上迁移，最终到达岩浆房顶部。长英质岩浆中富含挥发分流体的迁移运动是通过气泡的上浮实现的。气泡能否上浮主要取决于气泡的体积大小和受力的强度。只有体积较大的气泡才可能迅速迁移并到达岩浆房顶部。修正后的Ｄａｒｃｙ定律对气泡（岩浆体系中的流体）的上述运动特征给予了物理学方法的描述。

The formation of hydrothermal ore deposits,associated with magmatic fluids,to some extent,is the result of fluid evolution in magmatic system by compositions, pres-sures and properties.In a felsic magmatic system,crystallization of silicate minerals in-duces the formation of immiscible fluid, which exists in the form of fluid bubbles. Thevolume of these bubbles will increase with the progress of magma evolution.The fluidbubbles can finally rise to the upper boundary of magma chamber.In felsic magmatic sys-tem the migration of fluids rich in volatiles is resulted from the fluid bubbles' floating tothe surface of the magma chamber.The ability of the fluid bubbles' floating depends ontheir volumes and the forces act on them. Only the bigger fluid bubbles can quickly floatto the upper boundary of the magma chamber. Such migration characteristics can be de-scribed by the modified Darcy law, which is stated as:where j_i is the volumetric flow rate (i=1,2;1─immiscible fluid, 2 melt), μ_i is the dy-namic viscosity, k is the permeahlity, is the force, consisting of the pres-sure gradient plus a body force ρ_if_i.