Abstract
Relationship between magnetic anisotropy and lava viscosity:
The degree of the anisotropy of magnetic susceptibility (AMS) of basaltic rocks, as is known from the large AMS database of these rocks, is generally verb, low, while in more acidic volcanic rocks such as andesites, trachytes and phonolites, which have been investigated much less frequently, it is in general much higher. In the present study, the AMS of various volcanic rocks including trachytic and phonolitic rocks was investigated in the Tertiary volcanic region of the Ceske stredohori Mts. Viscosities of the respective lavas were calculated from the chemical composition using the KWARE program. A rough correlation was found between the degree of AMS and lava viscosities, probably resulting from. different mechanisms orienting the magnetic minerals. In basaltic lava flows this mechanism is traditionally considered to be of a hydrodynamic nature, in trachytic and phonolitic bodies it can also be represented by quasi-intrusive flows resembling, at least partially, ductile flow deformation. This is in agreement with the AMS data predicted by the viscous (liquid flow) and line/plane (ductile flow) models.