Heat and fluid flow in contact metamorphic aureoles with layered and transient permeability, with application to the Notch Peak aureole, Utah
Heat and fluid flow in contact metamorphic aureoles with layered and transient permeability, with application to the Notch Peak aureole, Utah
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DOI：
10.1029/2000jb900418
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发表时间：
2001-04
影响因子：
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通讯作者：
X. Cui;P. Nabelek;Mian Liu
中科院分区：
文献类型：
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作者：
X. Cui;P. Nabelek;Mian Liu
我们研究了层状和瞬态渗透性结构对接触变质晕中流体流动和热演化的控制作用，采用二维数值模拟方法，结合犹他州Notch Peak晕的岩石学和地球化学约束。该模型包括层间弱透水层和含水层岩性的地层和瞬态增强渗透性由于挥发分反应的规模。结果表明，分层渗透性结构导致流体集中进入含水层，导致流型强烈的时间依赖性和显着不同的预测简单的对流细胞均匀渗透性的光环。该模型预测了三种不同的流动状态的时间发展：（1）早期的径向低温流动由于岩浆流体的释放，（2）小的平面对流细胞附近的岩体-含水层接触在变质作用高峰期，（3）后期单向低温流动的上部光环和高温流动的中下部光环。当主岩的体积渗透率大于10−16 m2时，流动流体的热平流是显著的。在较低的体积磁导率，热传导占主导地位，和详细的渗透性结构上的温度场的影响变得微不足道。变质反应增强了内部光环的渗透性，使流体对流局部化，增加了流体通量。观察到的矿物组合和氧同位素的变化在上部分的Notch峰光环的空间分布与预测的时间积分的流体通量，这在变质作用的持续时间是由大量的水从岩体到围岩的低温流为主是一致的。
We have investigated the control of layered and transient permeability structures on fluid flow and thermal evolution in contact metamorphic aureoles using two-dimensional numerical modeling with petrological and geochemical constraints from the Notch Peak aureole, Utah. The model includes interbedded aquitard and aquifer lithologies on the scale of formations and transient enhancement of permeability due to devolatilization reactions. The results show that a layered permeability structure causes focusing of fluids into aquifer layers, resulting in flow pattern that is strongly time-dependent and significantly different from the predicted simple convection cells in aureoles with homogeneous permeability. The model predicts temporal development of three distinctive flow regimes: (1) early radial down-temperature flow due to release of magmatic fluid, (2) small flat convection cells near the pluton-aquifer contacts during peak metamorphism, (3) late unidirectional down-temperature flow in the upper aureole and up-temperature flow in the middle to lower aureole. When the bulk permeability of host rocks is >10−16 m2, heat advection by flowing fluids is significant. At lower bulk permeability, heat conduction dominates, and the effects of detailed permeability structure on the thermal field become negligible. Metamorphic reactions enhance permeability within the inner aureole, localizing fluid convection and increasing fluid flux. The observed spatial distribution of mineral assemblages and oxygen isotopic shifts in the upper part of the Notch Peak aureole is consistent with the predicted time-integrated fluid flux, which over duration of metamorphism is dominated by the down-temperature flow of a large amount of water from the pluton into the wall rocks.