Self‐Reversed Magnetization in Sediments Caused by Greigite Alteration
Self‐Reversed Magnetization in Sediments Caused by Greigite Alteration
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DOI：
10.1029/2023gl103885
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发表时间：
2023-06
影响因子：
5.2
通讯作者：
Liao Chang;Zhaowen Pei;P. Xue;Shishun Wang;Zhaoping Wang;W. Krijgsman;M. Dekkers
中科院分区：
文献类型：
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作者：
Liao Chang;Zhaowen Pei;P. Xue;Shishun Wang;Zhaoping Wang;W. Krijgsman;M. Dekkers
含云母岩沉积物中的多极性剩磁早已被认识到，但这种异常剩磁行为的原因还不是很清楚。在这里，我们使用电子显微镜和磁学分析来研究这种多极化的起源，在中新世含绿泥岩的沉积物中(匈牙利)。我们发现硫化物的磁软化和部分转变为磁铁矿和磁黄铁矿从“单极”到“多极”样品。硫化物颗粒向内的蚀变具有局部定向性，并与大小有关，小颗粒的蚀变程度较高。我们提出了蚀变云母中多相自逆转化学剩余磁化(CRM)机制：新形成的磁铁矿/磁黄铁矿壳层与云母核的原始剩余磁化方向相反，可能是通过紧密接触的核与壳之间的静磁相互作用或界面交换作用而获得的自逆转化学剩余磁化机制。这种新的云母自逆转模型可以解释通常观察到的反平行极性，并具有广泛的地质年代学、构造和古环境意义。
Multipolarity remanence in greigite‐bearing sediments has long been recognized, but the cause of this anomalous remanence behavior is not well understood. Here, we use electron microscopic and magnetic analyses to investigate the origin of such multipolarity in Miocene greigite‐bearing sediments from the Pannonian Basin (Hungary). We find a magnetic softening and partial transformation of iron sulfides to magnetite and pyrrhotite from “single‐polarity” to “multi‐polarity” samples. The inward alteration of sulfide grains is topotactic and is size‐dependent with higher alteration in smaller grains. We propose a multi‐phase self‐reversal chemical remanent magnetization (CRM) mechanism in altered greigite: the neoformed magnetite/pyrrhotite shell acquires a CRM coupled in the opposite direction to the primary CRM of the greigite core, likely through magnetostatic interactions or interfacial exchange interactions between the closely contacting core and shell. This new greigite self‐reversal model can explain the commonly observed antiparallel polarities and has broad geochronological, tectonic and paleoenvironmental implications.