Magnetic fabric of ignimbrites: a case study from the Central Anatolian Volcanic Province
Résumé
The magnetic fabric of the Pliocene Kızılkaya ignimbrite in the Central Anatolian Volcanic Province has been investigated by anisotropy of magnetic susceptibility (AMS) and isothermal remanent magnetization (AIRM). Seven sections were sampled at various stratigraphic heights within the devitrified portion of the ignimbrite. The magnetic mineralogy is complex: titanomagnetite occurs as magmatic grains, and as inclusions in other phenocryst and glass shards; an oxidized phase and hematite occur in deposit levels affected by alteration processes. The disturbance produced by lithic and pumice clasts has been reduced by discarding the specimens that deviate more than ±1σ from the site mean value of the density. The AMS fabric varies along each individual section. Neither the AMS magnetic lineation nor the magnetic foliation plunge clearly define a common area as the vent location. The AIRM fabric of low-coercivity minerals, mainly represented by free titanomagnetite grains of magmatic origin, is consistent between sites and the inferred flow directions converge on a region near Derinkuyu, in the Nevsehir plateau, previously reported as the Kızılkaya ignimbrite source area. This study shows that systematic use of the remanent fabric improves the results given by AMS and aids the identification of the primary magnetic fabric related to the ignimbrite emplacement dynamics.