Investigation of 3D magnetisation of a dolerite intrusion using airborne full tensor magnetic gradiometry (FTMG) data

in: Geophysical Journal International (2019)
Queitsch, Matthias; Schiffler, Markus; Stolz, Ronny; Rolf, Christian; Kukowski, Nina; Meyer, Matthias
Measurements of the magnetic field are one of the most used methods in geophysical exploration. In order to reduce the degree of ambiguity of this technique during inversion and modelling, data acquired by newly available gradiometer systems based on Superconducting Quantum Interference Devices (SQUIDs) are used. These systems provide measurements of the full magnetic gradient tensor of the Earth’s magnetic field, which offers a higher directional sensitivity than conventional total field magnetometers. A magnetization vector inversion (MVI) approach has been applied on data sets acquired over a dolerite intrusion in central Germany in order to model the full magnetization vector including remanent and induced components. Two different models have been created: one using only the magnetic total field anomaly (TFA) and the other based on five components of the magnetic gradient tensor. The two models show in principal the same structure, but the model based on the gradient tensor shows better defined structures. Also, magnetization amplitudes are closer to those measured on rock samples in this area. A comparison of the total magnetization vector of the rock samples and the models shows a better agreement in the vector direction of the gradient model compared to the total field model. A separation of induced and remanent contributions to the total magnetization has been performed and again shows better results when the gradient-based model is used. The effectiveness of the separation procedure will be discussed herein. The usage of gradiometer systems in an airborne geomagnetic exploration provides additional directional information, which is very helpful for MVIs. Compared to our model based on conventional TFA data, the gradient-based model features a much better agreement of the shape and magnetization of subsurface structures with those obtained from geologic−1al studies. The same, FTMGderived estimates of magnetization are more consistent with the results of measurements on rock samples.

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