Whole-Mantle Convection, Continent Generation, and Preservation of Geochemical Heterogeneity
Whole-Mantle Convection, Continent Generation, and Preservation of Geochemical Heterogeneity
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全地幔对流、大陆生成和地球化学不均匀性的保存
DOI：
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发表时间：
2008
期刊：
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通讯作者：
J. Baumgardner
中科院分区：
文献类型：
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作者：
U. Walzer;R. Hendel;J. Baumgardner
本文的重点是壳幔分异的数值模拟。我们从考察这一过程的观测限制开始。描述和讨论了不相容元素的现代分布。上述分异作用导致大陆的形成和增长，作为补充，亏损的MORB地幔(DMM)的产生和增加。在这里，我们提出了一个完整的理论来解决这个问题，该理论还包括了从内加热和从下加热的三维可压缩球壳地幔中的热固态对流。所用方程保证了238U-206Ph、235U-207Ph、232Th-208Ph、40K-40Ar对的质量、动量、能量、角动量和原子个数之和的守恒性。与压力和温度相关的粘度由粘塑性屈服应力σy补充。对大陆的数量、大小、形状和分布没有任何限制。只有接触到大陆的海洋高原才能与这块大陆相结合。这模仿了地体的吸积作用。数值结果是大陆总质量的阶段性增长，以及横向平均地表热流Qob、Urey数Ur和Rayleigh数Ra曲线的可接受过程。尽管有超过4500 Ma的固态地幔对流，我们通常会得到独立的，尽管不是简单地相连的地球化学地幔储集层。没有一个水库是没有混合的。这是朝着和解这一激动人心的问题迈出的一大步。正如预期的那样，DMM强烈地占据着大陆和大洋岩石圈的正下方。除此之外，结果是形成了一个大理石蛋糕状的地幔，但DMM在地幔的上半部分占优势。通过参数的综合变化，我们在Ra-σy图的中心部分发现了类似地球的大陆分布。也有Ra-σy区，计算的大陆总体积与观测值的偏差很小，Ur值可接受，地表热流符合实际。值得注意的是，所有这些不同的可接受Ra-σy区域共享共同的重叠区域。比较了观测到的现代地形谱和理论流动谱n1/2×(n+1)1/2×(v2n，pol1)。
The focus of this paper is numerical modeling of crust-mantle differentiation. We begin by surveying the observational constraints of this process. The present-time distribution of incompatible elements are described and discussed. The mentioned differentiation causes formation and growth of continents and, as a complement, the generation and increase of the depleted MORB mantle (DMM). Here, we present a solution of this problem by an integrated theory that also includes the thermal solid-state convection in a 3-D compressible spherical-shell mantle heated from within and slightly from below. The conservation of mass, momentum, energy, angular momentum, and of four sums of the number of atoms of the pairs 238U- 206Pb, 235U-207Pb, 232Th-208Pb, 40K-40Ar is guaranteed by the used equations. The pressure- and temperature-dependent viscosity is supplemented by a viscoplastic yield stress, σ y . No restrictions are supposed regarding number, size, form and distribution of continents. Only oceanic plateaus touching a continent have to be united with this continent. This mimics the accretion of terranes. The numerical results are an episodic growth of the total mass of the continents and acceptable courses of the curves of the laterally averaged surface heat flow, qob, the Urey number, Ur, and the Rayleigh number, Ra. In spite of more than 4500 Ma of solid-state mantle convection, we typically obtain separate, although not simply connected geochemical mantle reservoirs. None of the reservoirs is free of mixing. This is a big step towards a reconciliation of the stirring problem. As expected, DMM strongly predominates immediately beneath the continents and the oceanic lithosphere. Apart from that, the result is a marble-cake mantle but DMM prevails in the upper half of the mantle. We find Earth-like continent distributions in a central part of Ra-σy plot obtained by a comprehensive variation of parameters. There are also Ra-σy areas with small deviations of the calculated total continental volume from the observed value, with acceptable values of Ur and with realistic surface heat flow. It is remarkable that all of these different acceptable Ra-σy regions share a common overlap area. We compare the observed present-time topography spectrum and the theoretical flow spectrum n 1/2 × (n + 1)1/2 × (v 2 n,pol ).