Contact metamorphism surrounding the Alta Stock; finite element model simulation of heat- and 18 O/ 16 O mass-transport during prograde metamorphism
Contact metamorphism surrounding the Alta Stock; finite element model simulation of heat- and 18 O/ 16 O mass-transport during prograde metamorphism
复制标题
阿尔塔岩层周围的接触变质作用；
DOI：
10.2475/ajs.297.1.1
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发表时间：
1997
影响因子：
2.9
通讯作者：
C. Forster
中科院分区：
文献类型：
--
作者：
S. Cook;J. R. Bowman;C. Forster
阿尔塔斯托(犹他州)接触光环南段大理石的方解石-白云石地质测温和氧同位素研究结果为该地区广泛的热液变质作用提供了证据。用二维有限元流体流动和热传输模型模拟这两个独立的数据集，可以限制流体流动的模式、最小渗透率和这部分光环中的渗透率结构。模型结果表明，岩浆侵入均匀、各向同性渗透性介质产生的峰值变质温度显著低于在大理岩中测得的温度，并且在Alta-Grizzly逆冲系统上方和下方都有显著的{sup 18}O亏损。后者与南部光环中的观察结果相矛盾，即大理石中的氧亏损仅限于阿尔塔-灰熊逆冲冲断带以下的大理石；冲断带以上的白云质大理石直到侵入接触时仍保留原始沉积值。在Alta-Grizzly逆冲推覆体上方有水平渗透性屏障的模型，在Alta股票顶部延伸，能够再现观测到的南部极光的热和{Delta}{sup 18}O剖面。这种水平屏障的存在减少了在更均匀和各向同性渗透介质中主要发生的垂直流体流动和热传递，迫使流体流动和热传递横向远离料浆的上侧。这种水平流动模式对于在推力以上产生显著的氧消耗是必要的，并提供必要的横向热传递以复制观测到的温度分布。对观测到的温度和{Delta}{sup 18}O剖面的最佳拟合模型结果为南阿尔塔极光在变质过程中的流体循环动力学和水文地质特征提供了几个新的见解。
Results of calcite-dolomite geothermometry and oxygen isotope studies of marbles in the southern portion of the contact aureole surrounding the Alta stock (Utah) provide evidence for extensive hydrothermal metamorphism in this part of the aureole. Simulation of these two independent data sets with two-dimensional, finite element fluid flow and heat transport models constrains the pattern of fluid flow, minimum permeability, and the permeability structure in this part of the aureole. Model results demonstrate that intrusion of the stock into a homogeneous, isotropic permeability medium yields peak metamorphic temperatures significantly lower than those measured in the marbles and significant {sup 18}O depletions both above and below the Alta-Grizzly thrust system. The latter contradicts the observations in the south aureole that {sup 18}O depletions in the marbles are restricted to marbles below the Alta-Grizzly thrust; dolomitic marbles above the thrust retain original sedimentary values up to the intrusive contact. Models with horizontal permeability barriers above the Alta-Grizzly thrust and extending over the top of the Alta stock are capable of reproducing the observed thermal and {delta}{sup 18}O profiles in the southern aureole. The presence of such horizontal barriers reduces the predominantly vertical fluid flow and heat transfer that would occur in amore » homogeneous and isotropic permeability medium, forcing fluid flow and heat transfer laterally away from the upper flanks of the stock. Such horizontal flow patterns are necessary to produce significant {sup 18}O depletion above the thrust, and to provide the necessary lateral heat transfer to duplicate the observed temperature profile. Best fit model results to the observed thermal and {delta}{sup 18}O profiles provide several new insights into the dynamics of fluid circulation and hydrogeologic characteristics of the southern Alta aureole during prograde metamorphism.« less