The national baseline aeromagnetic survey of Britain allows a uniform assessment of the shallow and deep magnetic properties of the British tectonic terranes. The most significant is that associated with destruction of early Palaeozoic oceanic lithosphere across the Iapetus Suture separating Baltica and Avalonia from the Laurentian terranes. Here a formal 3D inversion of a continuous swathe of the data is considered. The study provides a uniform volumetric whole crust assessment extending for over 1000 km. Normally a 3D inversion of magnetic data is controlled using a variety of constraints however this is not appropriate at the crustal scale due to our increasingly imprecise knowledge of lithology at increasingly greater depths. The main crustal interface encountered occurs at the Curie isotherm depth. We demonstrate the behaviour of introducing different magnetic crustal depths and suggest the crustal ‘magnetic depth’ of our models can be independently constrained using global or regional studies of the deep geotherm. Static magnetic data have no inherent depth resolution. Here an empirical ‘1D depth’ weighting and a more formal ‘3D distance’ weighting are assessed. The inversion procedure is regularised to provide stable models appropriate to the data and their errors. To gain confidence when using such a ‘geologically-unconstrained’ inversion, we compare our 3D inversion results with an existing geologically-constrained 2.5D profile inversion across northern Britain. A surprising agreement in the 3D susceptibility magnitudes is observed. The chosen study area traverses 10 British terranes and images their tectonic fabric by way of non-magnetic zones (i.e. susceptibilities <0.0001 to 0.001 SI) and magnetic zones displaying geological relevance and tectonic significance at deeper crustal levels. Here we discuss the more significant 3D model features which, by virtue of a continuous crustal-scale assessment and fitting the data with a high degree of fidelity, provide additional structural insights.

英国的国家基线航磁测量允许对英国构造地体的浅层和深层磁特性进行统一评估。最重要的是与将波罗的海和阿瓦隆尼亚与劳伦地体分开的土卫六缝合线的早古生代海洋岩石圈的破坏有关。这里考虑了连续数据条带的正式 3D 反演。该研究提供了延伸超过 1000 公里的统一体积整体地壳评估。通常使用各种约束来控制磁数据的 3D 反演，但是由于我们对越来越深的岩性知识越来越不精确，这在地壳尺度上是不合适的。遇到的主要地壳界面发生在居里等温线深度。我们展示了引入不同磁性地壳深度的行为，并建议我们模型的地壳“磁性深度”可以使用深层地热的全球或区域研究独立约束。静磁数据没有固有的深度分辨率。这里评估了经验性的“1D 深度”权重和更正式的“3D 距离”权重。反演过程被正规化以提供适合数据及其误差的稳定模型。为了在使用这种“地质无约束”反演时获得信心，我们将我们的 3D 反演结果与英国北部现有的地质约束 2.5D 剖面反演进行了比较。观察到 3D 磁化率大小惊人的一致。选定的研究区域穿过 10 个英国地体，并通过非磁性带（即磁化率 <0.0001 至 0.001 SI）和磁性带在更深的地壳层显示地质相关性和构造意义，对其构造结构进行成像。在这里，我们讨论了更重要的 3D 模型特征，这些特征凭借连续地壳尺度评估和高度保真度拟合数据，提供了额外的结构见解。