Underground Fumaroles: Excess Heat Effects in Vein Formation
Underground Fumaroles: Excess Heat Effects in Vein Formation
复制标题
DOI：
10.2113/gsecongeo.95.3.453
复制
发表时间：
2000-05
期刊：
影响因子：
5.8
通讯作者：
R. Henley;G. Hughes
中科院分区：
文献类型：
--
作者：
R. Henley;G. Hughes
我们研究了热提取的断裂热液系统后，突然扩张的裂缝在寄主岩石。这种扩张增加了系统的渗透性，并且静脉沿着开口局部化的沿着不规则裂缝形成。为了简单起见，我们将在本文中考虑这样的静脉。假设系统中的流体最初接近蒸汽饱和，并与周围的寄主岩石处于热平衡。静脉的快速打开导致近似等焓的蒸气分离，并导致压降通过系统传播。由于裂缝系统中的两相流体受蒸汽压力曲线的约束，降压伴随着流体的快速冷却。流体流动也被诱导从热液储层朝向扩张的排出脉。裂缝系统中的寄主岩石和两相流体之间的温度差将热量从岩石驱入流体。以这种方式从主岩中获得的“多余的热量”[1][1]蒸发了两相流中的额外液体，这产生了比仅由于流体的快速初始绝热减压而产生的蒸汽分数大得多的蒸汽分数。因此，这种额外的蒸气分离导致液相中的高溶质浓度，并可能导致矿物在断裂系统和局部矿脉中更快地沉积。这里开发了一个模型来描述最小的“过量热”传递（即，最坏的情况）进入两相饱和液体/蒸气混合物，因为它从热液储层水平地被抽向排出矿脉。“过热”效应在活跃形成的脉纹的数十至数百米内被证明是有效的，并且是振荡条带和层压织物的主要原因。这种瞬态热提取过程适用于与脆性和脆韧性变形有关的各种浅部地壳存款类型。这些存款类型包括浅成热液富矿脉、海底块状硫化物矿床、剪切带中的中温热液脉、高温脉和高温热液成矿网和斑岩成矿网。[1]：#fn-1
We examine the heat extracted from a fractured hydrothermal system following the sudden dilation of fractures in the host rock. This dilation increases the permeability of the system, and veins form along irregular fractures where the opening is localized. For simplicity, we will consider one such vein in this paper. Fluid in the system is assumed to be initially close to vapor saturation and in thermal equilibrium with the surrounding host rock. The rapid opening of the vein leads to approximately isenthalpic vapor separation and causes a pressure drop to propagate through the system. As the two-phase fluid in the fracture system is constrained to the vapor-pressure curve, the depressurization is accompanied by a rapid cooling of the fluid. Fluid flow is also induced from a hydrothermal reservoir toward the dilated discharge vein. The temperature difference between the host rock and the two-phase fluid in the fracture system drives heat from the rock into the fluid. The "excess heat"[1][1] derived from the host rock in this manner evaporates additional liquid in the two-phase flow, which develops substantially larger vapor fractions than those due only to the rapid initial adiabatic depressurization of the fluid. Such additional vapor separation, therefore, leads to high solute concentrations in the liquid phase and potentially results in faster deposition of minerals in the fracture system and local veins. A model is developed here to describe the minimum "excess heat" transfer (i.e., the worst-case scenario) into the two-phase saturated-liquid/vapor mixture as it is drawn horizontally from the hydrothermal reservoir toward the discharge vein. "Excess heat" effects are shown to be effective within tens to hundreds of meters of actively forming veins and a principal cause of oscillatory banding and lamination fabrics. This transient heat extraction process applies to a wide range of shallow crustal deposit styles associated with brittle and brittle-ductile deformation. These deposit styles range from epithermal bonanza veins, sea-floor massive sulfide deposits, mesothermal veins in shear zones, to the higher temperature veins and stockworks of hypothermal and porphyry mineralization. [1]: #fn-1