Pressure‐to‐Depth Conversion Models for Metamorphic Rocks: Derivation and Applications
Pressure‐to‐Depth Conversion Models for Metamorphic Rocks: Derivation and Applications
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DOI：
10.1029/2020gc009280
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发表时间：
2020-12
期刊：
影响因子：
3.7
通讯作者：
A. Bauville;P. Yamato
中科院分区：
文献类型：
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作者：
A. Bauville;P. Yamato
压力-深度转换是地球动力学重建的关键步骤。最常用的压力-深度转换方法假定压力对应于静岩压力。然而，偏应力会导致压力强烈偏离静岩情况，从而增加压力-深度转换的不确定性。首先，我们重新推导了考虑偏应力的压力-深度转换公式。然后，我们在包含峰值和逆行变质压力数据的数据集中独立估计每个点的可能深度范围（单点法）。在第二次，我们同时使用岩石样品的峰值压力和逆行压力，假设这两个压力都是在同一深度记录的（两点法）。我们探索了不同的情况来解释从峰值到逆行压力的转变，通过改变应力的方向和大小。这种替代模型与所有数据点一致，但与单点模型相比，应力状态和深度的范围更受限制。结果表明：(1)即使小的偏应力也会对深度估计产生显著影响；(2)第二主应力分量σ2起着至关重要的作用；(3)几个模型可以解释数据的压力演变，但会导致深度估计的不同；(4)应变数据为我们提出的两点压力-深度转换提供了一个平均值。假设压力是静态的，峰值压力下的最大预测深度为170公里，而我们的两点模型的预测深度<75公里，这可能对应于地壳根莫霍的深度。
Pressure‐to‐depth conversion is a crucial step toward geodynamic reconstruction. The most commonly used pressure‐to‐depth conversion method assumes that pressure corresponds to the lithostatic pressure. However, deviatoric stresses can cause pressure to deviate from the lithostatic case strongly, thus adding considerable uncertainty to pressure to‐depth conversion. First, we rederive formulas of pressure‐to‐depth conversion that take into account deviatoric stresses. Then, we estimate the range of possible depth independently for each point in a data set containing peak and retrograde metamorphic pressure data (one‐point method). In a second time, we use both the peak and retrograde pressure of a rock sample together, assuming that both pressures were recorded at the same depth (two‐point method). We explore different cases to explain the transition from peak to retrograde pressure by varying the direction and magnitude of stresses. This alternative model is consistent with all data points but for a more restricted range of stress state and depth than the one‐point model. Our results show that (1) even small deviatoric stresses have a significant impact on depth estimates, (2) the second principal stress component σ2 plays an essential role, (3) several models can explain the pressure evolution of the data but lead to different depth estimates, and (4) strain data offer a mean to falsify our proposed two‐point pressure‐to‐depth conversion. The maximum predicted depth at peak pressure is 170 km using the assumption that pressure is lithostatic, compared to <75 km for our two‐point model, which could correspond to the crustal root Moho's depth.