Anisotropy of Magnetic Susceptibility (AMS) is a valid tool to investigate magma flow direction within dikes. However, geometrically inverse magnetic fabric characterized by maximum magnetic susceptibility axis (kmax) perpendicular to the dike wall may complicate the interpretation of flow trajectories. To better understand the nature of this fabric, we present a multiscale study on 19 dikes (383 samples) in the Miocene Alftafjordur volcanic system (Iceland), where 80% of the samples show a geometrically inverse magnetic fabric. We carried out (1) AMS measurements at different magnetic fields and temperatures, along with Anisotropy of Anhysteretic Remanent Magnetization (AARM) analysis; (2) hysteresis loops and FORC diagrams; (3) thin section analysis; (4) structural fieldwork. A variable Ti‐content (0.1 < x < 0.6, Fe_3‐xTi_xO₄) titanomagnetite is the main magnetic carrier, and the contribution of the paramagnetic elongated crystals to the magnetic fabric is negligible. Single domain is not the prevailing domain state of the magnetic particles, suggesting that its occurrence cannot be the main cause for the inverse fabric. AMS analysis at different fields and temperatures along with AARM allow us to exclude any mineral phase change of the titanomagnetite across the dike. Nevertheless, kmax is parallel to a diffuse horizontal column‐like fracture pattern perpendicularly oriented with respect to the dike strike. This suggests that the Ti‐magnetite mineral orientation during dike cooling was affected by the fracture network progressively developing columnar basalts. This study demonstrates that the interpretation of AMS data on old and deep volcanic bodies is not straightforward and observations at different scales are required.

中文翻译：

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解读冰岛东部中新世堤防中的逆磁结构

磁化率各向异性（AMS）是研究堤内岩浆流动方向的有效工具。但是，以垂直于堤壁的最大磁化率轴（kmax）为特征的几何形状相反的磁性织物会使流动轨迹的解释复杂化。为了更好地了解这种织物的性质，我们对中新世Alftafjordur火山系统（冰岛）中的19个堤坝（383个样品）进行了多尺度研究，其中80％的样品显示出几何形状相反的磁性织物。我们进行了（1）在不同磁场和温度下的AMS测量，以及各向异性磁化剩磁（AARM）分析的各向异性；（2）磁滞回线和FORC图；（3）薄断面分析；（4）结构实地考察。可变的Ti含量（0.1 <x <0.6，Fe _3-x钛_X Ø ₄钛磁铁矿是主要的磁性载体，而顺磁性细长晶体对磁性织物的贡献可忽略不计。单畴不是磁性粒子的主要畴状态，这表明它的出现不能成为反结构的主要原因。在不同场和温度下进行的AMS分析以及AARM使我们能够排除堤坝上钛磁铁矿的任何矿物相变。尽管如此，kmax平行于与堤坝走向垂直的弥散性水平柱状裂缝模式。这表明，在堤防冷却过程中，钛磁铁矿矿物的取向受到裂缝网络的影响，逐渐形成柱状玄武岩。