Flow directions in basaltic pahoehoe lavas from anisotropy of magnetic susceptibility data

SINGER SE; HALLER MJ; MENA M; RÉ GH; VILAS JFA

Potsdam

Congreso; 19th Colloquium on Latin American Geosciences; 2005

The Holocene Crater Basalt Volcanic Field, located in Northern Patagonia, constitutes an excellent location to apply the AMS method to determine flow directions and emplacement conditions.  Thus, first study of magnetic fabric was performed on these lava flows which they were sampled at different distances from the vent to recognize possible variations in the behavior of the flow.  Preliminary results show that the mean magnetic susceptibilities in all measured sited belong to moderately ferromagnetic rocks and both susceptibility and AMS are controlled by titanomagnetites. Proximal and mesial lava flow sections show larger scatter of the principal susceptibility axes related to distortions of the flow caused by degassing.  By the way, samples from the intermediate levels of distal levels of distal sections, with few vesicles, show more consistent magnetic fabrics.  The sites have oblate fabrics with well-defined magnetic foliation planes tilting downflow, reflecting the flow advance while the minimum principal axes plunge sourceward.