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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Evidence for a 20°tilting of the Earth's rotation axis 110 million years ago
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Evidence for a 20°tilting of the Earth's rotation axis 110 million years ago

机译：1.1亿年前地球自转轴倾斜20°的证据

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True polar wander (TPW), the shift of the Earth's rotation axis with respect to the entire globe, is most probably due to mass redistribution in the Earth's mantle as a result of convection. Using a new rigorously selected paleomagnetic database gathering only directions obtained from magmatic rocks, we find that TPW has been clearly intermittent over the last 200 Myr with two long periods of strict standstill from the present to 80 Ma and from approximately 150 to 200 Ma. A single period of shifting is observed, between 80 and about 150 Ma. This period culminates around 110 Ma in an 20°abrupt tilting during which an angular speed exceeding 5°/Myr (0.5 m/yr) may have been reached. Assuming that the time-averaged geomagnetic field is axial, our results indicate that the changes in the position of the rotation axis, and therefore in the inertia tensor of the Earth, are intermittent. We suggest that a major reorganization of the mass distribution in the Earth's mantle occurred in the Lower Cretaceous. This event, concomitant with plume hyperactivity at the Earth's surface and probable drastic changes at the core-mantle boundary attested by the inhibition of geomagnetic reversals, suggests unmixing of upper and lower mantle by avalanching of upper mantle material down to the core-mantle boundary. The astonishingly strict stability of the time-averaged position of the rotation axis before and after this episode of shifting implies the existence of some steady convection which does not modify the large-scale distribution of mass within the mantle. Given the intermittence of mantle avalanching, we suggest that these long periods of stability correspond to the temporary reestablishment of a basically two-layered convection system within the mantle.
机译：真正的极地游走（TPW），即地球自转轴相对于整个地球的位移，很可能是由于对流导致地幔中的物质重新分布。使用仅收集从岩浆岩获得的方向的严格选择的新古地磁数据库，我们发现TPW在过去的200 Myr期间明显是断断续续的，从现在到80 Ma以及从大约150到200 Ma都有两个长时间的严格停顿。观察到一个单周期的偏移，在80至150 Ma之间。这个周期在20°突然倾斜时达到110 Ma左右，在此期间可能达到超过5°/ Myr（0.5 m / yr）的角速度。假设时间平均地磁场是轴向的，我们的结果表明旋转轴位置的变化以及地球惯性张量的变化都是间歇性的。我们建议在下白垩统发生地幔质量分布的重大重组。该事件伴有地球表面的羽状活动过度，以及地磁逆转的抑制，证明了地幔边界可能发生剧烈变化，这表明上地幔和下地幔的混合是通过上地幔物质崩塌到地幔幔边界来实现的。旋转轴的时间平均位置在此偏移之前和之后的惊人的严格稳定性意味着存在一些稳定的对流，这不会改变地幔内部质量的大规模分布。考虑到地幔雪崩的间歇性，我们建议这些长期的稳定性对应于地幔内基本两层对流系统的临时重建。

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