| dc.description.abstract | In the last decades low-field magnetic susceptibility measurements have become an increasingly attractive method for geological studies which use the scalar values (bulk susceptibility) as well as the directional information, the anisotropy of magnetic susceptibility (AMS). Because of the potential for detecting weak fabric anisotropies, AMS has become a routine method for assessing flow directions in magmatic bodies. Sources of AMS in ferrimagnetic basaltic rocks are mainly titanomagnetites. After Jackson et al. (1998) and de Wall (2000), the magnetic susceptibility (MS) of titanomagnetite varies strongly with mineral composition and is in the low-field range strongly depending on the field amplitude of the inducing magnetic field. Here we present a systematic study to record the effects of field dependence on AMS of dykes, sills and lava flows. Variation in MS characteristics have been found indicative for lava emplacement and flow dynamics (Cañón-Tapia et al. 1997, Cañón-Tapia & Pinkerton 2000). The contribution of the effect of field dependence on MS and AMS in titanomagnetite-bearing volcanic rocks needs to be assessed for a reliable interpretation of AMS variations. The key study has been carried out at the Ság-hegy volcanic complex in the Little Hungarian Plain. It is composed of a phreatomagmatic tuff ring, formed during the pliocene-miocene period. After meteoric water supply ended, the phreatomagmatic eruptive style changed into an effusive behaviour and the tephra ring was filled with a lava lake and a dyke-sill complex transected the pyroclastic successions. We report AMS characteristics of sills, dykes and lavas from the lake interior and outflowing lava deposits. Furthermore we discriminated samples that represent the transition from dykes to sills and from intrusive (dyke) to effusive (lava flow) emplacement, respectively. The MS has been measured by a KLY-4S kappabridge (AGICO, Brno) which allows a record of the AMS at a high sensitivity and in various field amplitudes (2 to 450 A/m). | en_US |
