Mechanisms for oscillatory true polar wander
Mechanisms for oscillatory true polar wander
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DOI：
10.1038/nature11571
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发表时间：
2012-11-08
期刊：
影响因子：
64.8
通讯作者：
Matsuyama, I.
中科院分区：
文献类型：
--
作者：
Creveling, J. R.;Mitrovica, J. X.;Matsuyama, I.
对古元古代至白垩纪岩石的古地磁研究（1-5）提出了一系列相对于地表地理的旋转极的大而相对快速（在1000万至1亿年内为数十度）的偏移，或真极漂移（TPW）。这些漂移可能以振荡的、近似共轴的方式围绕着同时代的超大陆中心连续发生（5-7）。在标准旋转理论（8、9）的框架内，旋转凸起的延迟粘性调整起到稳定旋转轴（10）的作用，振荡TPW的地球动力学模型通常要求具有可比量级的连续、相反加载阶段（6、11、12）。在这里，我们扩展了一个非线性旋转稳定性理论（10），以纳入TPW引起的岩石圈弹性应力的稳定效应（13，14）。我们证明，对流驱动的惯性扰动作用在一个近扁长，非流体静力学地球（6，7）的有效弹性岩石圈厚度约为10公里，产生振荡TPW路径与古地磁推断一致。如果旋转轴通过TPW平面内的长期过量椭圆率而稳定，则弹性厚度的这种估计可以减小，甚至减小到零。我们推测，这些稳定的来源，作用于TPW驱动的随时间变化的地幔流场（11，12，15 -18），提供了一种机制，连接不同的，振荡TPW事件的过去几十亿年。
Palaeomagnetic studies(1-5) of Palaeoproterozoic to Cretaceous rocks propose a suite of large and relatively rapid (tens of degrees over 10 to 100 million years) excursions of the rotation pole relative to the surface geography, or true polar wander (TPW). These excursions may be linked in an oscillatory, approximately coaxial succession about the centre of the contemporaneous supercontinent(5-7). Within the framework of a standard rotational theory(8,9), in which a delayed viscous adjustment of the rotational bulge acts to stabilize the rotation axis(10), geodynamic models for oscillatory TPW generally appeal to consecutive, opposite loading phases of comparable magnitude(6,11,12). Here we extend a nonlinear rotational stability theory(10) to incorporate the stabilizing effect of TPW-induced elastic stresses in the lithosphere(13,14). We demonstrate that convectively driven inertia perturbations acting on a nearly prolate, non-hydrostatic Earth(6,7) with an effective elastic lithospheric thickness of about 10 kilometres yield oscillatory TPW paths consistent with palaeomagnetic inferences. This estimate of elastic thickness can be reduced, even to zero, if the rotation axis is stabilized by long-term excess ellipticity in the plane of the TPW. We speculate that these sources of stabilization, acting on TPW driven by a time-varying mantle flow field(11,12,15-18), provide a mechanism for linking the distinct, oscillatory TPW events of the past few billion years.