The effects of deep water cycling on planetary thermal evolution
The effects of deep water cycling on planetary thermal evolution
复制标题
深水循环对行星热演化的影响
DOI：
10.1029/2011jb008405
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发表时间：
2011
影响因子：
--
通讯作者：
P. McGovern
中科院分区：
文献类型：
--
作者：
C. Sandu;A. Lenardic;P. McGovern
[1]我们使用一个参数化的对流模型来研究深水循环对类地行星热演化的影响。该模型包括两个水库，一个表面和内部地幔水库。两者之间的交换计算使用地幔对流参数化，允许温度和水依赖的地幔粘度连同内部自洽脱气和再放气参数化。脱气和再气之间的平衡取决于构造板块的平均扩张速率、分配到熔体中的水量、地幔熔体区的厚度以及俯冲板块顶部的水化层的厚度。脱气与熔融区厚度成比例，使得早期的广泛熔融将产生更干燥和更粘的地幔，使固相线在将减小熔融区厚度和地幔热损失速率的方向上移动。耦合水化区厚度依赖的再气化因子的模型，模仿水输送到地幔通过蛇纹层，允许一个潜在的逆转点的整体水流方向切换从脱气再气化地幔冷却。水对粘度的影响产生了一种负反馈，这种负反馈往往会调节地幔中的最终水量，因此它不会强烈依赖于行星水的初始量。地表水库中的最终水量由这种反馈效应以及整个地球的初始水量预算决定。这意味着，如果可以从行星形成模型中估计出行星的初始水预算，那么地表水的体积就可以用来估计类地行星地幔中的水体积。将这种方法应用于地球，导致地球地幔中的水浓度预测符合地球化学和岩石学的限制。
[1] We use a parameterized convection model to investigate the effects of deep water cycling on the thermal evolution of an Earth-like planet. The model incorporates two water reservoirs, a surface and an interior mantle reservoir. Exchange between the two is calculated using a mantle convection parameterization that allows for temperature- and water-dependent mantle viscosity together with internally self-consistent degassing and regassing parameterizations. The balance between degassing and regassing depends on the average spreading rate of tectonic plates, the amount of water partitioned into melt, the thickness of a mantle melt zone, and of a hydrated layer at the top of subducting plates. Degassing scales with melt zone thickness such that an early period of extensive melting would create a drier and more viscous mantle, shifting the solidus line in a direction that would reduce the melt zone thickness and the rate of mantle heat loss. Coupling a hydrated zone thickness-dependent regassing factor to the model, to mimic water delivery to the mantle via a serpentinized layer, allows for the potential of a reversing point where the overall water flow direction switches from degassing to regassing as the mantle cools. The water effect on viscosity creates a negative feedback that tends to regulate the final amount of water in the mantle so it is not strongly dependent on the initial amount of planetary water. The final amount of water in the surface reservoir is then determined by this feedback effect together with the initial water budget of the entire planet. This implies that if the initial water budget of a planet can be estimated, from planetary formation models, then the volume of surface water can be used to estimate the volume of water in the mantle of an Earth-like planet. Applying this methodology to the Earth leads to predictions for water concentration in the Earth's mantle that are in line with geochemical and petrological constraints.