An integration to optimally constrain the thermal structure of oceanic lithosphere
An integration to optimally constrain the thermal structure of oceanic lithosphere
复制标题
优化约束海洋岩石圈热结构的集成
DOI：
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发表时间：
2013
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通讯作者：
J. Hillier
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文献类型：
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作者：
B. Goutorbe;J. Hillier
海洋岩石圈随时间的演化是一个重大的、尚未完全解决的地球动力学问题。关于其热结构、物理特性以及统一观测约束的最佳模型，目前仍难以达成共识。我们通过（i）同时拟合从上地幔剪切速度模型得出的热流、测深和温度，（ii）使用三个主要热模型（半空间、板块和夏布利），以及（iii）分析五个深度年龄曲线，其中使用对比技术来排除海底深度的异常特征，从而有力地重新评估了所有这三个模型。热模型均已更新，包括与温度相关的热容、与温度和压力相关的热导率以及包括熔化在内的绝热减压的初始条件。半空间模型让岩石圈无限增厚，无法准确拟合沉降曲线，并且需要过高的地幔位温 Tm。另一方面，包括基础供热机制的模型能够同时解释两个标准误差内的所有观测结果，并且最佳拟合参数对过滤测深曲线的选择具有鲁棒性。对于在固定深度施加恒定温度的板模型，Tm 在 1380–1390°C 范围内变化，平衡板厚度 a 在 106–110 km 范围内变化，体积热膨胀系数 α 变化在 2.95−3.20 ⋅ 10−5 K−1 范围内。对于夏布利斯模型，它规定了增厚岩石圈底部的固定热流，最佳拟合值为 Tm = 1320−1380°C，a = 176−268 km，α ́=3.05−3.60⋅10−5 K−1。在更准确的海洋深度的驱动下，板块模型为观测提供了更好的联合拟合；然而，它需要低于实验测量的 α 值，这可以通过上层岩石圈的弹性刚度导致表观膨胀率的降低来解释。当 α 设定为接近或高于实验值时，Chablis 模型可以更好地拟合数据。尽管在两个标准误差内统计上一致，但观测到的深度年龄曲线与地震得出的温度之间的不相容趋势以新的清晰度揭示出来，因为后者没有表现出明显的稳态，而前者则趋于平坦；需要进一步的工作来确定这种明显差异的根源。这项工作为完全独立于热方程的特定解的研究开辟了道路。
The evolution through time of the oceanic lithosphere is a substantial, incompletely resolved geodynamical problem. Consensus remains elusive regarding its thermal structure, physical properties, and the best model through which to unify observational constraints. We robustly reevaluate all three of these by (i) simultaneously fitting heat flow, bathymetry, and temperatures derived from a shear velocity model of the upper mantle, (ii) using the three main thermal models (half‐space, plate, and Chablis), and (iii) analyzing five depth‐age curves, wherein contrasting techniques were used to exclude anomalous features from seafloor depths. The thermal models are updated to all include a temperature‐dependent heat capacity, a temperature‐ and pressure‐dependent thermal conductivity, and an initial condition of adiabatic decompression including melting. The half‐space model, which lets the lithosphere thicken indefinitely, cannot accurately fit the subsidence curves and requires mantle potential temperatures, Tm, that are too high. On the other hand, the models including a mechanism of basal heat supply are able to simultaneously explain all observations within two standard errors, with best‐fitting parameters robust to the choice of the filtered bathymetry curve. For the plate model, which imposes a constant temperature at a fixed depth, Tm varies within 1380–1390°C, the equilibrium plate thickness a within 106–110 km, and the bulk thermal expansivity α¯ within 2.95−3.20 ⋅ 10−5 K−1. For the Chablis model, which prescribes a fixed heat flow at the base of a thickening lithosphere, the best‐fitting values are Tm = 1320−1380°C, a = 176−268 km, α¯=3.05−3.60⋅10−5 K−1. Driven by more accurate ocean depths, the plate model provides better joint‐fittings to the observations; however, it requires values of α¯ lower than experimentally measured, which can be explained by a reduction of the apparent expansivity due to elastic rigidity of the upper lithosphere. The Chablis model better fits the data when α¯ is set close to or above the experimental values. Although statistically consistent within two standard errors, a tendency toward incompatibility between observed depth‐age curves and seismically derived temperatures is revealed with new clarity, because the latter do not exhibit a clear steady state whereas the former flatten; further work is needed to identify the origin of this apparent discrepancy.This work opens the way to investigations fully independent of particular solutions of the heat equation.