Mantle convection and evolution with growing continents
Mantle convection and evolution with growing continents
复制标题
地幔对流和大陆生长的演化
DOI：
10.1029/2007jb005459
复制
发表时间：
2008
影响因子：
--
通讯作者：
R. Hendel
中科院分区：
文献类型：
--
作者：
Walzer;R. Hendel
我们提出了一个三维球壳数值模型，用于对流地球地幔中不相容元素的化学分异和再分布，主要由U，Th和K内部加热，略从下面加热。演化模型方程保证了质量、动量、能量、角动量以及238 U-206 Pb、235 U-207 Pb、232 Th-208 Pb和40 K-40 Ar对原子数的四个总和的守恒。与压力和温度相关的粘度由粘塑性屈服应力σy补充。岩石圈粘度的增加部分是由海洋岩石圈脱水和其他效应引起的。软流层的形成不仅取决于温度和熔融温度的分布，更重要的是取决于水溶解度和水丰度的分布。因此，我们引入了描述该行为的径向粘度分布因子。然而，本文的重点是大陆和海洋高原的幕式增长。作为一种补充，分异作用产生的亏损MORB地幔（DMM），占主导地位的岩石圈之下。我们的大陆不是人为地强加在球壳的表面上，而是通过化学分化和对流/混合之间的相互作用而演变的。对大陆的数量、大小、形式和分布没有任何限制。然而，撞击大陆的海洋高原必须与大陆结合在一起，这类似于火山岩的增生。数值结果表明，一个情节的增长的大陆的总质量和显示一个合理的时间历史的横向平均表面热流，qob和瑞利数，Ra。我们用我们的模型来探索Ra-σ y参数空间的一个适度区域。我们发现类地大陆分布在我们探索的Ra-σ y空间的中心部分。我们确定了一个Ra-σ y区域，其中计算出的大陆总体积非常接近观测值;另一个Ra-σ y区域，其中Urey数Ur接近公认值;第三个Ra-σ y区域，其中表面热流非常接近当今观测到的平均全球热流，使用典型的产热元素丰度。值得注意的是，这些不同的可接受Ra-σ y区域共享一个共同的重叠区域，在那里同时实现了类似地球的行为。尽管对流流型和海洋高原的化学分异是耦合的，但与时间相关的瑞利数Rat的演变相对较好地预测，并且Rat（t）曲线的随机部分很小。关于大陆总质量的幼年生长率的时间分布，假设初始条件给定，只有在进化的第一个时期才有可能进行预测。后来，大陆增长事件的分布越来越随机。独立于不同的个体运行，我们的模型表明，现今大陆的总质量不是在地球热演化开始时的单一过程中产生的，而是在周期性分布的过程中产生的。这与观察结果雅阁。
We present a three‐dimensional spherical shell numerical model for chemical differentiation and redistribution of incompatible elements in a convective Earth's mantle heated mostly from within by U, Th, and K and slightly from below. The evolution‐model equations guarantee conservation of mass, momentum, energy, angular momentum, and four sums of the number of atoms of the pairs238U–206Pb,235U–207Pb,232Th–208Pb, and40K–40Ar. The pressure‐ and temperature‐dependent viscosity is supplemented by a viscoplastic yield stress,σy. The lithospheric viscosity is partly imposed to mimic its increase by dehydration of oceanic lithosphere and other effects. Also, the asthenosphere is generated not only by the distribution of temperature and melting temperature, but essentially by the profiles of water solubility and water abundance. Therefore we introduced a radial viscosity profile factor describing that behavior. However, the focus of this paper is the episodic growth of continents and oceanic plateaus. As a complement, the differentiation generates the depleted MORB mantle (DMM) which predominates immediately beneath the lithosphere. Our continents are not artificially imposed on the surface of the spherical shell, but instead they evolve by the interplay between chemical differentiation and convection/mixing. No restrictions are imposed regarding number, size, form, and distribution of continents. However, oceanic plateaus that impinge upon a continent have to be united with it. This mimics the accretion of terranes. The numerical results show an episodic growth of the total mass of the continents and display a plausible time history for the laterally averaged surface heat flow,qob, and the Rayleigh number,Ra. We use our model to explore a moderate region ofRa–σyparameter space. We find Earth‐like continent distributions in a central part of theRa–σyspace we explored. We identified aRa–σyregion where the calculated total continental volume is very close to the observed value; anotherRa–σyregion where the Urey number,Ur, is close to the accepted value; a thirdRa–σyarea where surface heat flow is very close to the present‐day observed mean global heat flow using typical abundances of the heat‐producing elements. It is remarkable that these different acceptableRa–σyregions share a common overlap area, where Earth‐like behavior is simultaneously fulfilled.Although the convective flow patterns and the chemical differentiation of oceanic plateaus are coupled, the evolution of time‐dependent Rayleigh number,Rat, is relatively well predictable and the stochastic parts of theRat(t) curves are small. Regarding the time distribution of juvenile growth rates of the total mass of the continents, predictions are possible only in the first epoch of the evolution, presumed that the initial conditions are given. Later on, the distribution of the continental growth episodes is increasingly stochastic. Independent of the varying individual runs, our model shows that the total mass of the present‐day continents is not generated in a single process at the beginning of the thermal evolution of the Earth but in episodically distributed processes. This is in accord with observation.
登录
查看更多内容
内华达试验场不稳定岩石的分布：与核试验地面运动预测的比较
DOI：
--
发表时间：
2003
期刊：
影响因子：
--
作者：
J. Brune;D. V. Seggern;A. Anooshehpoor
通讯作者：
A. Anooshehpoor
早期地球：物理、化学和生物发展
DOI：
--
发表时间：
2003
期刊：
影响因子：
--
作者：
C. Fowler;C. Ebinger;C. Hawkesworth
通讯作者：
C. Hawkesworth
厚球壳内无限普朗特数的变粘度热对流
DOI：
--
发表时间：
1997
期刊：
影响因子：
--
作者：
W. Yang
通讯作者：
W. Yang
DOI：
--
发表时间：
1989
期刊：
影响因子：
--
作者：
D. Howell
通讯作者：
D. Howell
中地幔粘度和相变结构对三维地幔对流的影响
DOI：
--
发表时间：
2000
期刊：
影响因子：
--
作者：
L. Cserepes;D. Yuen;B. Schroeder
通讯作者：
B. Schroeder