Emplacement of the Puy de Dôme Investigated Using Structural, Anisotropy of Magnetic Susceptibility, Paleomagnetic and Rock Magnetic Data

Abstract:

This study uses detailed geological mapping and various geophysical methods (anisotropy of magnetic susceptibility (AMS), rock magnetic, and paleomagnetic data) to understand the emplacement mechanism of the Puy de Dôme located in south-central Auvergne, France. Geologic mapping shows that the Puy de Dôme has a smooth NE-SSW facing side with the opposite side being a steeper ridged area separated by a major ridge orientated NNE-SSW on the south side and a fault on the north side. The western side is bounded by two ridges that are strongly foliated and have an approximate 270° bearing in the basal sections and rotates towards 290° towards the summit. The remaining ridges are massive and unfoliated, yet often humpback in shape. Eleven paleomangetic/AMS/rock magnetic sampling sites were collected via standard acquisition methods during summer of 2013 while an additional eight sites were drilled during summer of 2014. For the preliminary sites, AMS data shows strong oblate fabrics for all eleven sites, Curie point data suggests that all magnetic carrier for all sites are dominated by titanomagnetite. Preliminary paleomagnetic data reveal two possible remanence directions. We argue either a hiatus in the eruption highlighted by slight rotation or, alternatively, the variation in site mean data may reflect secular variation or a tectonic disturbance. We propose that these These data indicate an original dome being deformed and pushed upwards and outwards as magma filled in major faults. This deformation resulted in two “hinges” on either side forming strong foliations along the hinge line while the rest of the ridged area remained unfoliated to the west and smooth to the east. We argue that the Puy de Dôme was erupted from a NE-SW oriented fissure that pierced the surface. The dome was buttressed on the NE and E side by the Peitit-Puy de Dôme Bulge, but free to extend SE to form the elongated ridge. The dome reached a height sufficient to flow laterally to the west and developed a bulge to this side as the flow initiated, but never managed to flow more than a few tens of meters.