One- and two-dimensional models of fluid flow and stable isotope exchange at an outcrop in the Adamello contact aureole, Southern Alps, Italy
One- and two-dimensional models of fluid flow and stable isotope exchange at an outcrop in the Adamello contact aureole, Southern Alps, Italy
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意大利南阿尔卑斯山阿达梅洛接触光环露头处的流体流动和稳定同位素交换的一维和二维模型
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发表时间：
1995
期刊：
影响因子：
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通讯作者：
D. Rumble
中科院分区：
文献类型：
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作者：
M. Gerdes;L. Baumgartner;M. Person;D. Rumble
摘要意大利阿尔卑斯山南部阿达梅洛接触晕中薄的近水平大理岩层中~(18)O和~(13)C的局部性亏损是沿横切岩脉集中的流体渗入所致。方解石方解石中δ18O和δ13C的值从δ18O=22‰(Smow)和δ13C=0‰(Pdb)系统地递减到脉岩附近的δ18O=12.5‰和δ13C≈-7‰。在花岗闪长岩脉附近5-15厘米厚的大理岩层中发现的斜长石和石榴石表明了富含H2O的流体条件(Xco₂≈0.01)。氧和碳同位素剖面与一维和二维平流-弥散同位素输运模型进行了比较。就个别而言，同位素分布很好地符合一维输运模型。然而，考虑到渗入流体的岩石学约束，使用平衡流体交换或动力学公式的一维模型不能解释两个同位素交换剖面的相对位置或形状。使用一个二维模型获得了与δ18O和δ13C数据很好的一致性，该模型指定(1)大理岩中靠近岩脉的高渗透区集中了平行于岩脉的流体流动，(2)远离岩脉的大理岩中的低渗透区，其中同位素交换以分子扩散为主。通过相平衡和两个同位素示踪剂的组合约束，可以从一维数据中推断出二维流体流动。结果强调，如果单独考虑同位素示踪，多维流动产生的同位素分布可能碰巧符合一维输运模型。因此，结合流体成分限制使用多种示踪剂对于区分不同的输送模式是至关重要的。
Abstract Localized depletion of 18O and 13C in a thin subhorizontal marble layer in the Adamello contact aureole, Southern Alps, Italy, resulted from fluid infiltration focused along a crosscutting dike. Values of δ18O and δ13C in calcite from the 1 m long profile decrease systematically from sedimentary values of δ18O = 22‰(SMOW) and δ13C= 0‰(PDB) to δ18O = 12.5‰ and δ13C ≈ -7‰ near the dike. The presence of clinozoisite and garnet in the 5-15 cm thick marble layers near the granodiorite dike indicates H2O-rich fluid conditions (XCO₂ ≈ 0.01 ). The O and C isotope profiles were compared with one- and two-dimensional models of advective-dispersive isotope transport. Individually the isotope profiles fit one-dimensional transport models well. However one-dimensional models, using equilibrium fluidrock exchange or a kinetic formulation, do not explain the relative locations or shapes of the two isotope-exchange profiles given the petrologic constraint of XCO₂ ≈ 0.01 for the infiltrating fluid. Excellent agreement with the δ18O and δ13C data is obtained using a twodimensional model that specifies (1) a high-permeability zone in marble near the dike that focuses fluid flow parallel to the dike and (2) a lower permeability zone in marble away from the dike where isotope exchange is dominated by molecular diffusion. The combined constraints imposed by phase equilibria and two isotope tracers allow two-dimensional fluid flow to be inferred from one-dimensional data. The results emphasize that isotope distributions resulting from multidimensional flow may fortuitously fit one-dimensional transport models if isotope tracers are considered independently. The use of multiple tracers coupled to fluid-composition constraints is therefore essential to discriminate between various transport models.