Continental insulation, mantle cooling, and the surface area of oceans and continents [rapid communication]
Continental insulation, mantle cooling, and the surface area of oceans and continents [rapid communication]
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DOI：
10.1016/j.epsl.2005.01.038
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发表时间：
2005-06
影响因子：
5.3
通讯作者：
A. Lenardic;Louis Moresi;A. Jellinek;M. Manga
中科院分区：
文献类型：
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作者：
A. Lenardic;Louis Moresi;A. Jellinek;M. Manga
一般认为，大陆作为对流地幔上方的热绝缘体，抑制了地球内部的热损失。我们目前的理论，数值模拟和实验室实验来测试这个直观的和常用的假设的有效性。发展了一个标度理论来预测部分被稳定大陆岩石圈覆盖的对流地幔的热流。该理论预测，参数制度的存在，增加大陆绝缘对地幔热流没有影响，甚至可以提高它。部分绝缘导致内部地幔温度升高和粘度降低。这反过来又使海洋岩石圈更快地翻转，增加了海洋热通量。根据大陆与海洋表面积的比例，全球地幔热流可以保持不变，甚至因此而增加。理论结垢分析与数值模拟和实验室实验的结果是一致的。将我们的结果应用于地球，我们发现，与传统的理解相反，大陆绝缘一般不会减少全球热流。这种绝缘可以有一个可以忽略不计的影响，甚至加强地幔冷却，这取决于地幔粘度的温度依赖性的大小。这一理论还表明了对大陆表面积的潜在限制。表面积的增加提高了大洋岩石圈的俯冲速率。如果大陆是在俯冲环境中产生的，这可能会增强大陆的生长，达到一个临界点，在这个临界点上，绝缘的增加会导致对流应力水平下降到接近岩石圈屈服应力的值。这种情况使得脆弱的板块边缘难以维持，这反过来又降低了俯冲速度，限制了大陆的进一步增长。该理论被用来预测临界点作为地幔热流的函数。对于地幔热损失率，预测的大陆表面积与观测值雅阁。
It is generally assumed that continents, acting as thermal insulation above the convecting mantle, inhibit the Earth's internal heat loss. We present theory, numerical simulations, and laboratory experiments to test the validity of this intuitive and commonly used assumption. A scaling theory is developed to predict heat flow from a convecting mantle partially covered by stable continental lithosphere. The theory predicts that parameter regimes exist for which increased continental insulation has no effect on mantle heat flow and can even enhance it. Partial insulation leads to increased internal mantle temperature and decreased viscosity. This, in turn, allows for the more rapid overturn of oceanic lithosphere and increased oceanic heat flux. Depending on the ratio of continental to oceanic surface area, global mantle heat flow can remain constant or even increase as a result. Theoretical scaling analyses are consistent with results from numerical simulations and laboratory experiments. Applying our results to the Earth we find, in contrast to conventional understanding, that continental insulation does not generally reduce global heat flow. Such insulation can have a negligible effect or even enhance mantle cooling, depending on the magnitude of the temperature dependence of mantle viscosity. The theory also suggests a potential constraint on continental surface area. Increased surface area enhances the subduction rate of oceanic lithosphere. If continents are produced in subduction settings this could enhance continental growth up to a critical point where increased insulation causes convective stress levels to drop to values approaching the lithospheric yield stress. This condition makes weak plate margins difficult to maintain which, in turn, lowers subduction rates and limits the further growth of continents. The theory is used to predict the critical point as a function of mantle heat flow. For the Earth's rate of mantle heat loss, the predicted continental surface area is in accord with the observed value.