HR: 1340h
AN: T13A-0422    [Abstracts]
TI: Magnetic anisotropy of the subcontinental mantle: a proxy for seismic anisotropy?
AU: * Belley, F
EM: fanfan24@siu.edu
AF: Departement of Geology, Southern Illinois University, Carbondale, IL 62901 United States
AU: Ferre, E C
EM: eferre@geo.siu.edu
AF: Departement of Geology, Southern Illinois University, Carbondale, IL 62901 United States
AU: Martin-Hernandez, F
EM: fatima@geo.uu.nl
AF: Paleomagnetic Laboratory 'Fort Hoofddijk', Utrecht University, Utrecht, CD 3584 Netherlands
AU: Vauchez, A
EM: alain.vauchez@dstu.univ-montp2.fr
AF: Laboiratoire Tectonophysique, Universite de Montpellier II, Montpellier, 34095 France
AU: Garrido, C J
EM: carlosg@ugr.es
AF: Instituto Andaluz de Ciencias de la Terra, Universidad de Granada, Campus Fuentenueva sln, Granada, 18002 Spain
AB: Our knowledge of the petrology and seismic properties of the subcontinental mantle is deduced mostly from three sources: (i) large scale seismic anisotropy investigations; (ii) non-oriented mantle xenoliths and (iii) rare peridotite bodies such as the Ronda massif. These three sources provide information at different scales, from grain size (xenoliths and peridotitic bodies) to tens of kilometers (seismology). Xenoliths exhibit lattice-preferred orientation (LPO) due to plastic flow in the mantle, which, in turns, results in seismic anisotropy. Similarly, seismic waves propagating beneath continents display variations in speed and polarization direction attributed to the mantle deformation history. An implicit correlation is generally assumed between the two anisotropies measured at these very different scales. A new magnetic technique, investigating an intermediate scale, has been developed in the past few years. This technique measures the anisotropy of magnetic susceptibility in high field, using a vibrating sample magnetometer to saturate the ferromagnetic minerals. Therefore it effectively isolates the paramagnetic and diamagnetic susceptibility anisotropy. Magnetic measurements, performed on various high field instruments (vibrating sample magnetometer, torque magnetometer, cantilever magnetometer), both on natural and synthetic samples, confirm the need to conduct measurements in high field in order to isolate the intrinsic paramagnetic and diamagnetic properties of olivines, orthopyroxenes and clinopyroxenes. These measurements also demonstrate the orthorhombic nature of the intrinsic magnetic properties in these silicates, and yield new data concerning the relationship between crystallographic axes, magnetic anisotropy and other physical anisotropies. Seismic anisotropies of a suite of Ronda peridotites are calculated, using a forward modeling approach (Anis2K) and measured LPOs. The same LPOs are used to calculate magnetic anisotropies, using new single crystal magnetic data and a similar approach. Finally, calculated magnetic and seismic anisotropies are compared with measured magnetic anisotropies to evaluate the potential of magnetic fabrics as a proxy for seismic anisotropy in the subcontinental mantle.
DE: 8100 TECTONOPHYSICS
DE: 8194 Instruments and techniques
SC: Tectonophysics [T]
MN: Fall Meeting 2005