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Magneto-mineralogical characterisation of the Bažina Maar (CZ) volcanic rocks to reconstruct their emplacement conditions

Magneto-mineralogical properties of volcanic rocks can be used to study their emplacement conditions and thus the eruptive behaviour of volcanoes. Two ICDP cores were drilled into the effusive and explosive units of the Bažina Maar, located in the Czech Republic. The drilled volcanic units are up to 160 m thick in total, and consist of lapilli tuff and effusive (sub-)volcanic rocks which are overlain by unconsolidated, highly weathered lapilli and scoria deposits. The units are locally overprinted by apatite-bearing sequences, possibly of hydrothermal origin. We used a KLY-5A Kappabridge to measure the out-of-phase (op) in addition to the traditionally measured in-phase (ip) temperature-dependent magnetic susceptibility and determined Curie-Temperatures (Tc), field depend magnetic susceptibility as well as the anisotropy of magnetic susceptibility (AMS). The most common sources for an op component in igneous rocks are vicous relaxation of superparamagnetic/single domain (titano-)magnetite grains and weak field hysteresis of ferrimagnetic phases like titanomagnetite and pyrrhotite. Ip and op Tcs between 170 – 300°C suggest a Ti-rich titanomagnetite as the main ferrimagnetic phase. Higher Tcs within the explosive products between 450 – 580°C suggest maghemitisation of the juvenile titanomagnetite. The ip AMS component for the effusive volcanic rocks reveals a moderate to steeply inclined magnetic foliation, suggesting an upwards flow as emplacement mechanism. For the lapilli units, the op AMS response is oblique to the ip AMS signal, revealing a magnetic subfabric. Our study demonstrates that the systematic study of ip and op susceptibility can add key information to unravel complex volcanological processes.

Details

Author
Johanna Berckhan1, Agnes Kontny1
Institutionen
1Karlsruhe Institute of Technology, Germany
Veranstaltung
GeoSaxonia 2024
Datum
2024
DOI
10.48380/ezvd-t845