Department of Geological and Mining Engineering and Sciences, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931, USA.; Department of Physics, Michigan Technological University, Houghton, MI 49931, USA.
Centre for Earth Evolution and Dynamics, University of Oslo, N-0315 Oslo, Norway.
Sci Adv. 2017 Feb 15;3(2):e1602306. doi: 10.1126/sciadv.1602306. eCollection 2017 Feb.
Many geodynamo models predict an inverse relationship between geomagnetic reversal frequency and field strength. However, most of the absolute paleointensity data, obtained predominantly by the Thellier method from bulk volcanic rocks, fail to confirm this relationship. Although low paleointensities are commonly observed during periods of high reversal rate (notably, in the late Jurassic), higher than present-day intensity values are rare during periods of no or few reversals (superchrons). We have identified a fundamental mechanism that results in a pervasive and previously unrecognized low-field bias that affects most paleointensity data in the global database. Our results provide an explanation for the discordance between the experimental data and numerical models, and lend additional support to an inverse relationship between the reversal rate and field strength as a fundamental property of the geodynamo. We demonstrate that the accuracy of future paleointensity analyses can be improved by integration of the Thellier protocol with low-temperature demagnetizations.
许多地磁场动力学模型预测地磁场反转频率与磁场强度之间存在反比关系。然而，大多数通过 Thellier 方法从块状火山岩中获得的绝对古强度数据未能证实这种关系。尽管在高反转率期间（特别是在侏罗纪晚期）通常观察到低古强度，但在无反转或反转次数少的时期（超旋回），很少出现高于现今强度值的情况。我们已经确定了一种普遍存在且以前未被认识到的低场偏差的基本机制，该机制会影响全球数据库中大多数古强度数据。我们的结果为实验数据与数值模型之间的不一致提供了解释，并为反转率与场强之间的反比关系作为地磁场动力学的基本性质提供了额外的支持。我们证明，通过将 Thellier 协议与低温退磁相结合，可以提高未来古强度分析的准确性。
