Rochechouart impact crater melt breccias record no geomagnetic field reversal
Rochechouart impact crater melt breccias record no geomagnetic field reversal
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DOI：
10.1016/j.epsl.2013.11.021
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发表时间：
2014-02
影响因子：
5.3
通讯作者：
M. Eitel;S. Gilder;T. Kunzmann;J. Pohl
中科院分区：
文献类型：
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作者：
M. Eitel;S. Gilder;T. Kunzmann;J. Pohl
撞击熔融角砾岩从罗什舒阿尔特（法国）陨石坑具有古地磁方向与正常和反向极性，提出了一个问题，是否冲击碰撞引发了地磁场逆转。逐步热退磁连同一套岩石磁性实验，光学显微镜，拉曼光谱和电子探针分析确定相邻的，多相的，钛赤铁矿的样品中含有正常和混合极性的典型的岩性轴承自反转行为源于磁交换相互作用。熔融角砾岩拥有大部分无钛的赤铁矿作为剩磁载体，只有相反的极性方向，从而得出结论，罗什舒阿尔特陨石的影响并没有产生地磁事件。显示正常或混合极性的古地磁方向的样品产生不可靠的古强度数据。30个具有相反极性的样品通过了Thellier-Thellier古强度实验的严格数据选择标准，并进行了蚀变、尾部和加和性检查，确定了平均场值为12.8±3.7 μT。这转化为2.7±0.8× 1022 Am 2的虚拟偶极矩，这是相对较低的，但在其他中生代古强度数据的不确定性。
Impact melt breccias from the Rochechouart (France) meteorite crater possess paleomagnetic directions with both normal and reverse polarities, raising the question whether shock from the collision initiated a geomagnetic field reversal. Stepwise thermal demagnetization together with a suite of rock magnetic experiments, optical microscopy, Raman spectroscopy and electron microprobe analyses identify adjacent, multiphase, titanohematite in the samples containing normal and mixed polarities—typical of lithologies bearing self-reversal behavior stemming from magnetic exchange interaction. Melt breccias possessing mostly titanium-free hematite as the magnetic remanence carrier have solely reverse-polarity directions, leading to the conclusion that the Rochechouart meteorite impact did not spawn a geomagnetic event. Samples displaying paleomagnetic directions with normal or mixed polarity yield unreliable paleointensity data. 30 samples with reverse polarity that pass stringent data selection criteria from Thellier–Thellier paleointensity experiments with alteration, tail and additivity checks define an average field value of 12.8±3.7 μT. This translates into a virtual dipole moment of 2.7±0.8× 10 22 A m 2, which is relatively low, but within uncertainty of other Mesozoic paleointensity data.