Magnetic susceptibility of pre- and post caldera lavas from Maninjau, West Sumatra

Abstract

Lake Maninjau was formed after a caldera forming eruption ∼50,000 years ago. Eventhough this eruption is one of the biggest Quarternary eruptions on Sumatra, it is not studied in detail so far. Only few attempts to study the volcanic processes have been carried out, mainly focusing on stratigraphy, physical volcanologoical parameters and geochemical characterization of volcanic rocks around the lake but the magnetic susceptibility of the pre- and post caldera lava have not been studied. Identification of the magnetic susceptibility of rocks can be done by using Bartington Magnetic Susceptibility Meter type MS2B. This study aims to determine the concentration of magnetic minerals based on the value of magnetic susceptibility in rocks. The Magnetic susceptibility data can be used as initial characteristics to understand the volcanic processes in the past and explain the environmental changes processes. The magnetic susceptibility values obtained ranged from 967.8 × 10−8 m3/kg - 2187.0 × 10−8 m3/kg. This Range indicates that the sample is estimated to be dominated by ilmenite (FeTiO3). Further frequency dependent susceptibility (χfds%) defined as ratio of magnetic susceptibility measured with difference frequency ranges less than 1%. Our results show all the samples are virtually no superparamagnetic and generally dominated by multi-domain (MD) grains.