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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 >Paleomagnetism of impact spherules from Lonar crater, India and a test for impact-generated fields
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Paleomagnetism of impact spherules from Lonar crater, India and a test for impact-generated fields

机译：来自印度罗纳火山口的撞击球的古磁性及其对撞击产生场的测试

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摘要

Planetary surfaces have been ubiquitously melted by meteoroid impacts throughout solar system history. The resulting impact melts form some of the youngest igneous samples from rocky bodies like the Moon, Mars, and asteroids. Upon cooling, these melts may record any ambient planetary magnetic fields as well as postulated transient fields generated by impact plasmas. Impact-generated fields have been proposed as a key alternative to the core dynamo hypothesis for the paleomagnetism of extraterrestrial bodies. Here we describe a paleomagnetic study of basaltic impact glasses from the Lonar impact crater situated in the Deccan Traps in Maharashtra, India. Previous theoretical work predicts extremely strong magnetic fields (possibly >1,000 times the Earth's surface field) may have been transiently generated during the Lonar impact. We find that the glasses contain a natural remanent magnetization (NRM) whose properties depend strikingly on sample mass. Small (<0.5. g), splash-form samples demagnetize erratically and are inefficiently magnetized, while larger, irregularly shaped samples contain a stable component that is efficiently magnetized similar to Lonar basalts. However, the rock magnetic recording properties of these samples are uncorrelated with mass. Therefore, we conclude that the size dependence of the NRM reflects a difference in how the samples acquired thermoremanence. The splash forms of the smaller samples indicate they cooled during flight and therefore that they were magnetized while in motion, explaining their weak and unstable NRM. This motional NRM is a new manifestation of thermoremanent magnetization not observed before in geologic samples. No glasses contain evidence for any strong (>~100 μT) impact-generated fields.
机译：在整个太阳系历史上，流星体的撞击已使行星表面无处不在。由此产生的冲击融化形成了一些来自诸如月球，火星和小行星等岩石物体的最年轻的火成岩样品。冷却后，这些熔体可能会记录任何周围的行星磁场以及撞击等离子体产生的假定瞬变场。已经提出了冲击产生的场，作为地球外星体古磁性的核心发电机假说的关键替代方法。在这里，我们描述了位于印度马哈拉施特拉邦Deccan陷阱的Lonar撞击坑中玄武岩撞击玻璃的古磁研究。先前的理论工作预测，在月球撞击期间可能会瞬间产生极强的磁场（可能是地球表面场的1000倍）。我们发现玻璃杯包含自然剩磁（NRM），其性质显着取决于样品质量。较小的（<0.5 g）飞溅状样品会消磁，并且磁化效率低下，而较大的不规则形状的样品中含有稳定的成分，类似于Lonar玄武岩，它会被有效磁化。但是，这些样品的岩石磁记录特性与质量无关。因此，我们得出的结论是，NRM的尺寸依赖性反映了样品在获得热剩磁方面的差异。较小样本的飞溅形式表明它们在飞行过程中冷却，因此它们在运动时被磁化，从而说明了它们的NRM弱且不稳定。这种运动型NRM是以前在地质样品中未观察到的热剩磁的新表现。没有任何眼镜可以证明存在任何强烈（>〜100μT）冲击场。

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