Simple models for the Beattie Magnetic Anomaly in South Africa
Simple models for the Beattie Magnetic Anomaly in South Africa
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DOI：
10.1016/j.tecto.2008.11.027
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发表时间：
2009-11
期刊：
影响因子：
2.9
通讯作者：
Y. Quesnel;U. Weckmann;O. Ritter;J. Stankiewicz;V. Lesur;M. Mandea;B. Langlais;B. Langlais;C. Sotin;A. Galdeano
中科院分区：
文献类型：
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作者：
Y. Quesnel;U. Weckmann;O. Ritter;J. Stankiewicz;V. Lesur;M. Mandea;B. Langlais;B. Langlais;C. Sotin;A. Galdeano
南非大约1000公里长的贝蒂磁异常（BMA）的起源仍然不清楚，也有争议。关键问题包括其源的宽度、深度和磁化强度。在这项研究中，我们使用均匀磁化的球体，棱柱体和圆柱体，以提供最简单的可能的模型，预测1公里高度的航磁测量沿着剖面跨越BMA。通过正演模拟调整震源参数。在球体的情况下，应用反演技术来细化参数。我们的研究结果表明，两个类似的磁化和相邻的源，垂直偏移，可以解释所观察到的磁异常。最佳拟合模型对应于两个高度磁化（>5 A m−1）的片状棱镜，分别从9至12 km深度和13至18 km深度延伸，总宽度达到80 km。其他不太受欢迎的模型显示更厚和更深的磁化体积。相关的磁化似乎主要是诱导的，虽然弱recrystallization组件是必需的，以提高适合。我们还比较了我们的结果与解释独立的大地电磁和地震实验沿着同一剖面。这表明，BMA的地质来源主要位于中地壳，并可能被剪切带或断层所取代。与以前的模型表明，在纳塔尔-纳马夸移动的带的古洋壳的蛇纹石化银，我们建议，麻粒岩相中地壳岩石在这个带可能会导致BMA。
The origin of the approximately 1000 km-long Beattie Magnetic Anomaly (BMA) in South Africa remains unclear and contentious. Key issues include the width, depth and magnetization of its source. In this study, we use uniformly magnetized spheres, prisms and cylinders to provide the simplest possible models which predict the 1 km-altitude aeromagnetic measurements along a profile across the BMA. The source parameters are adjusted by forward modeling. In case of a sphere, an inversion technique is applied to refine the parameters. Our results suggest that two similarly magnetized and adjacent sources, with a vertical offset, can explain the observed magnetic anomaly. The best fitting model corresponds to two highly-magnetized (>5 A m−1) sheet-like prisms, extending from 9 to 12 km depth, and from 13 to 18 km depth, respectively, and with a total width reaching 80 km. Other less-preferred models show thicker and deeper magnetized volumes. Associated magnetizations seem to be mostly induced, although a weak remanent component is required to improve the fit. We also compare our results with the interpretation of independent magnetotelluric and seismic experiments along the same profile. It suggests that the geological sources for the BMA are mostly located in the middle crust and may be displaced by a shear zone or a fault. Contrary to previous models suggesting a serpentinized sliver of paleo-oceanic crust within the Natal–Namaqua Mobile Belt, we propose that granulite-facies mid-crustal rocks within this belt may cause the BMA.