Young inner core inferred from Ediacaran ultra-low geomagnetic field intensity
Young inner core inferred from Ediacaran ultra-low geomagnetic field intensity
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DOI：
10.1038/s41561-018-0288-0
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发表时间：
2019-02-01
影响因子：
18.3
通讯作者：
Cottrell, Rory D.
中科院分区：
文献类型：
--
作者：
Bono, Richard K.;Tarduno, John A.;Cottrell, Rory D.
关于地球的一个持久的谜团是其固体内核的年龄。合理但对比鲜明的核心热导率值导致内核生长起始年龄跨越20亿年，从近似0.5亿年到> 25亿年前。古地磁数据提供了过去的核心条件的直接探测，但迄今为止，缺乏最年轻的预测内核开始年龄的场强数据。在这里，我们提出了古强度数据从埃迪卡拉纪（类似于5.65亿岁）七岛侵入套件测量单斜长石和单斜辉石晶体托管单域磁性包裹体。这些数据表明，时间平均的偶极矩近似为0.7 × 10（22）A m（2），这是迄今为止关于现存岩石中地球发电机的最低值，比现在的磁场强度小十倍以上。这些晶体的古地磁定向研究定义了两个极性，在低纬度具有异常高的角色散（S =类似于26度）。连同其他14个方向的数据集，建议超反转频率，这些非常低的磁场强度表明一个异常的领域的行为，符合预测的地球发电机模拟，高导热性和埃迪卡拉纪开始年龄的内核增长。
An enduring mystery about Earth has been the age of its solid inner core. Plausible yet contrasting core thermal conductivity values lead to inner core growth initiation ages that span 2 billion years, from similar to 0.5 to >2.5 billion years ago. Palaeomagnetic data provide a direct probe of past core conditions, but heretofore field strength data were lacking for the youngest predicted inner core onset ages. Here we present palaeointensity data from the Ediacaran (similar to 565 million years old) Sept-Iles intrusive suite measured on single plagioclase and clinopyroxene crystals that hosted single-domain magnetic inclusions. These data indicate a time-averaged dipole moment of similar to 0.7 x 10(22) A m(2), the lowest value yet reported for the geodynamo from extant rocks and more than ten times smaller than the strength of the present-day field. Palaeomagnetic directional studies of these crystals define two polarities with an unusually high angular dispersion (S = similar to 26 degrees) at a low latitude. Together with 14 other directional data sets that suggest a hyper-reversal frequency, these extraordinary low field strengths suggest an anomalous field behaviour, consistent with predictions of geodynamo simulations, high thermal conductivities and an Ediacaran onset age of inner core growth.