Magnetic Fabrics and Source Implications of Chisulryoung Ignimbrites, South Korea

Abstract

The anisotropy of magnetic susceptibility (AMS) of late Cretaceous ash-flow tuffs in Chisulryoung Volcanic Formation, southeastern Korea was studied to define the primary pyroclastic flow azimuth. AMS data revealed a dominant oblate fabric with a tight clustering of k 3 (minimum axis of magnetic susceptibility) and shallow dispersal of k 1 (maximum axis of magnetic susceptibility) and k 2 (intermediate axis of magnetic susceptibility). Dominance of oblate fabrics indicates clast imbrications imposed by compaction and welding. Flow azimuth inferred from AMS data indicates the nearby intrusive welded tuff (IWT) as the source of calderas for ignimbrites. Such an inference is supported by geologic investigations, in which the IWT displays eutaxitic textures nearly parallel to its subvertical contacts. The results are compatible with a unique prolate fabric and an anomalously high inclination observed for the IWT, possibly produced by rheomorphic flows as the welded tuff is squeezed along the rough-surfaced dyke walls due to agglutination.

AMS and rock magnetism in the Caviahue-Copahue Volcanic Complex (Southern Andes): Emission center, flow dynamics, and implications to the emplacement of non-welded PDCs

“…In the past decades the AMS has been extensively applied to pyroclastic deposits, mainly as a tool for source area identification (e.g., Palmer and MacDonald, 1999;Hong et al, 2016;Alva-Valdivia et al, 2017). Despite that, few studies have examined how AMS relates to flow dynamics (e.g., Fisher et al, 1993;Baer et al 1997;Ort et al, 2003Ort et al, , 2014Giordano et al, 2008;LaBerge et al, 2009).…”