HR: 0830h
AN: GP11D-0289    [PDF]
TI: An Example of Inverse Magnetic Fabric in a Lava Pile From the Kerguelen Archipelago
AU: * Plenier, G
EM: rochette@cerege.fr
AF: Earth Science Departement, University California, Santa Cruz, CA 95064 United States
AU: Bascou, J
EM: jerome.bascou@dstu.univ-montp2.fr
AF: ISTEEM, Universit‚ Montpellier 2, Montpellier, 34095 France
AU: Gattacceca, J
EM: gattacceca@cerege.fr
AF: CEREGE, BP80, Aix en Provence, 13545 France
AU: Camps, P
EM: pierre.camps@dstu.univ-montp2.fr
AF: ISTEEM, Universit‚ Montpellier 2, Montpellier, 34095 France
AU: Rochette, P
EM: rochette@cerege.fr
AF: CEREGE, BP80, Aix en Provence, 13545 France
AB: Because of their low degree of anisotropy associated with a relatively high magnetic susceptibility, AMS measurements of lava flows often provide scattered results and a large number of sample is needed to well define the mean directions. However, the use of complementary AMS methods combined with other technics allow to infer flowing directions of lava piles. Such a study was performed on six volcanic sections (9 up to 20 lava flows) from the Kerguelen Archipelago(southern Indian Ocean) in order to complete regional geological observations of Nougier (1970) and identify the locations of the different eruptive centers. Unfortunately, one of these sequences, the Mont de la RabouillŠre, yielded an unexpected inverse fabric which did not allowed us to undoubtly interpret its flowing direction. We thus present a detailed analysis of this particular section including an additional AMS study on the same samples but at a demagnetized state. To complete this approach, we determined the anhysteretic remanent anisotropy (ARA) of theses samples to compare the magnetic fabrics obtained. Also further rock magnetic studies were performed. Normal and high resolution FORC analysis of one sample per flow were realized in order to detect eventual characteristic signatures associated with the inverse fabric. Endly, an Electron BackScattered Diffraction analysis (EBSD) of one thin section allowed to determine the cristalline orientation of the plagioclases to check its relation with the magnetic signal. Surprisingly, the [001] axis of the plagioclase minerals was found to be aligned with the mean kmax determined using the AMS. The study is still on progress but our preliminary interpretations indicate that the inverse magnetic fabric can be used to infer a confident flowing direction for this section. J. Nougier, 1970. Contribution a l'etude geologique et geomorphologique des iles Kerguelen. C.N.F.R.A., Vol 27, 2 tomes, 440pp and 256pp
DE: 1518 Magnetic fabrics and anisotropy
DE: 8439 Physics and chemistry of magma bodies
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting