HR: 14:55h
AN: NS33A-06    [Abstracts]
TI: High Resolution Geophysical Characterization of Fractures within a Granitic Pluton
AU: * Pérez-Estaśn, A
EM: aperez@ija.csic.es
AF: CSIC-Institute of Earth Sciences "Jaume Almera", Lluís Solé i Sabarís s/n, Barcelona, 08028S, Spain
AU: Carbonell, R
EM: rcarbo@ija.csic.es
AF: CSIC-Institute of Earth Sciences "Jaume Almera", Lluís Solé i Sabarís s/n, Barcelona, 08028S, Spain
AB: The FEBEX underground gallery was excavated in the Aar Granite (Switzerland), a heterogeneous granite containing from very leucocratic facies to granodiorites. The geology of the gallery shows the existence of various sets of fractures with different attributes: geometry, kinematics, fracture infilling, etc. The study of the structural data, new observations on the FEBEX gallery itself and borehole televiewer data acquired in the newly drilled boreholes, have allowed to identify four sets of fractures. The first group of fractures has a typical distribution and characteristics of en echelon tension fractures and were formed in late magmatic stages, according with the paragenesis of the minerals that filled the craks. The main strike is around 300 (280-300). These fractures are deformed and displaced by the other group of faults. The second group corresponds to the lamprophyre dikes, of mantelic origin, with an orientation oblique to the tunnel, and slightly oblique to the first group of fractures (strike, 310-330). They were formed during an extension event well evidenced by their irregular margins and flame structures into the granite. The margins of these dikes show several reactivations as strike slip faults. Geophysical data has been acquired to characterized the fracture network of the surrounding volume within the FEBEX gallery. The geophysic data include new borehole logging such as Natural Gamma and Borehole Ground Penetrating radar. The processing and integration of these different data sets indicates that the GPR record can provide images of a third set of fractures, which are probably fluid filled. This set of fractures a subparallel to the tunnel axis and appear to intersect older boreholes which are nearly perpendicular to the axis of the FEBEX gallery.
DE: 8010 Fractures and faults
SC: Near-Surface Geophysics [NS]
MN: 2007 Fall Meeting