Reconstruction of ancient volcanic complexes using magnetic signature: A case study from Cambrian andesite lava flow, Bohemian Massif

Abstract

Reconstruction of the Upper Cambrian Křivoklát-Rokycany Volcanic Complex was made using anisotropy of magnetic susceptibility (AMS). The correlation of AMS with visible structures at a few sites showed that the most important and reliable information was the direction of magnetic lineation K1 that determines the direction of a lava flow. The analysis of K1 directions together with radially propagating dikes helped to determine the feeding area along the NW rim of the volcanic complex. One andesite feeder and one rhyodacite feeder were recognized with certainty. In addition, K1 directions pointed to a suspicious area with the presence of another andesite feeder in a caldera-like structure. The evaluation of data strongly suggests that magnetic susceptibility in andesite lavas increases with the distance from the feeder and also with the distance towards the upper part of the andesitic lava flow. We suggest that this might be related to the degree of oxidation of the lava flow before solidification as a reaction with oxygen in the atmosphere. Oxygen can react with FeO in the andesite melt, which consequently results in the formation of magnetite.