نتايج اوليه مطالعه ناهمسانگردي مغناطيس پذيري در توده گرانيتوييدي شاهكوه (جنوب بيرجند)

The Preliminary Study of Magnetic Susceptibility (MS) in the Pluton of Shah-Kuh Granitoid; South of Birjand

The measurement of anisotropy of magnetic susceptibility is a suitable technique for quantifying the magnetic fabric of a pluton using cores with 25 mm diameter and 50 to 100 mm length. The origin of magnetic fabrics in granites is mainly described in terms of orientation of crystals, which occured during deformation of cooling magma before its complete crystallisation. In this paper, principles of anisotropy of magnetic susceptibility (AMS) and its applications in determination of magnetic fabrics of Shah-Kuh is presented. The magnitude of magnetic susceptibility in different units of this pluton ranges between 79 to 2896 n SI. These values, as well as Fe-content in different specimens, indicate that minerals responsible for anisotropy of magnetic susceptibility are mainly magnetite, hornblende and biotite, in lesser significance. Accordingly, Shah-Kuh granite, except its greisenic granite and leucocratic microgranite, could be classified as ferromagnetic granite. This conclusion confirms the earlier petrological studies, which classified Shah-Kuh granite as an I- type granites. The presence of tourmaline in the greisenic granite and leucocratic microgranite results in an inverse magnetic fabric. Such rocks, due to their inverse magnetic fabric, need more detail AMS study. Nearly vertical magnetic foliation, observed in the some specimens, probably represents their primary location in the wall of pluton. Specimens with vertical magnetic lineations, from granodiorites adjacent to of Deh- Margh village, may be evidence of magma feeder zone.