Anisotropy of magnetic susceptibility constraints on the emplacement mechanism of the Kuhe-Cheft intrusion, Toroud– Chah Shirin arc, NE Iran

This study investigates the emplacement mechanism of the Kuhe-Cheft subvolcanic intrusion, located within the Toroud–Chah Shirin magmatic arc and the northern part of the Central Iranian structural zone, using Anisotropy of Magnetic Susceptibility (AMS) method. The host rocks consist of Eocene volcano-sedimentary units, including volcanic breccias, agglomerates, and red sandy tuffs. The intrusion is mineralogically composed of plagioclase phenocrysts, hornblende needles, biotite, and minor amounts of magnetite and apatite. The measured bulk magnetic susceptibility values classify the intrusion as a ferromagnetic granitoid. AMS data reveal a steep, concentric magnetic foliation along the intrusion margins. Oblate susceptibility ellipsoids observed near the roof zone, a high anisotropy degree oriented along the intrusion's short axis, and the intense fracturing of the surrounding rocks—particularly along the western contact—all support a ballooning emplacement mechanism. The similarity of magnetic fabric patterns between Kuhe-Cheft and adjacent intrusions suggests syn-tectonic emplacement under a dextral transpressional regime. On a regional scale, the left-lateral Anjilow and Toroud strike-slip faults reflect a right-lateral transpressional stress field. The andesitic magmas likely ascended through extensional openings within the shear zone and emplaced via ballooning at the rheological boundary with the Eocene host rocks.