Abstract Interpretations of flow fabrics in dikes using anisotropy of magnetic susceptibility (AMS) are based on the orientation of the magnetic fabric recorded next to the dike walls. However, uncertainties remain when AMS is sensitive to parameters such as grain size and composition of the magnetic carriers and deformation of the magma. We study subvolcanic andesite to dacite dikes associated with granite plutons that intrude the basement rocks. The dikes have magnetic susceptibilities mostly between 10−3 and 10−2 SI carried by Fe–Ti oxides. AMS shows fabrics that would be consistent with a lateral movement of the magma. However, the anisotropy of anhysteretic remanence (AAR) and silicate shape preferred orientation (SPO) indicate that the melt moved upward based on the steeply plunging lineations detected by AAR and SPO. Furthermore, the obliquity of the AAR foliations in the dike margins indicates a component of transtension resolved in the dike walls. As there is no evidence for internal deformation of titanomagnetite, AMS would record its late growth in the tectonic extension direction. The magnetic subfabric concealed by late AMS therefore documents an earlier tectonic episode and evidence the limits of using just AMS directions to constrain the emplacement of syntectonic magmas.

中文翻译：

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复合岩浆/磁性织物证明了 Monteiro-Sumé 深成岩-火山复合体（巴西东北部）同构造岩脉中的晚期 AMS

摘要 使用磁化率各向异性 (AMS) 来解释堤防中的流动织物是基于堤壁旁边记录的磁性织物的方向。然而，当 AMS 对磁性载体的粒度和成分以及岩浆变形等参数敏感时，不确定性仍然存在。我们研究了亚火山安山岩到英安岩与侵入基底岩石的花岗岩岩体相关的岩脉。这些岩脉的磁化率主要在 10-3 和 10-2 SI 之间，由 Fe-Ti 氧化物携带。AMS 显示了与岩浆横向运动一致的织物。然而，非磁滞剩磁 (AAR) 和硅酸盐形状择优取向 (SPO) 的各向异性表明，基于 AAR 和 SPO 检测到的急剧下降的线形，熔体向上移动。此外，堤岸边缘的 AAR 叶理的倾斜度表明了堤墙中解析的张力分量。由于没有钛磁铁矿内部变形的证据，AMS 将记录其在构造伸展方向上的晚期生长。因此，晚期 AMS 隐藏的磁性亚结构记录了较早的构造事件，并证明了仅使用 AMS 方向来限制同构造岩浆侵位的局限性。