HR: 0800h
AN: GP21A-0150 [Abstracts]
TI: Combined Neutron Texture And Magnetic Analyses On "Undeformed" Clays: The Origin Of Tectonic Lineations
In Extensional Basins
AU: * Cifelli, F
EM: cifelli@uniroma3.it
AF: Dipartimento Scienze Geologiche, Universit
Roma TRE, Largo S.Leonardo Murialdo,1, Rome, 00146
Italy
AU: Mattei, M
EM: mattei@uniroma3.it
AF: Dipartimento Scienze Geologiche, Universit
Roma TRE, Largo S.Leonardo Murialdo,1, Rome, 00146
Italy
AU: Chadima, M
EM: chadima@sci.muni.cz
AF: Institute of Geology, Academy of Sciences of the Czech Republic, Rozvojov 135, Praha 6, Praha,
CZ-16502
Czech Republic
AU: Hirt, A M
EM: hirt@mag.ig.erdw.ethz.ch
AF: Insitut fr Geophysik, ETH, Schafmattstrasse 30,
ETH Hnggerberg, Zrich, 8093
Switzerland
AU: Hansen, A
EM: Anke.Hansen@gkss.de
AF: Institut fr Werkstoffkunde und Werkstofftechnik,
GKSS-Forschungszentrum
, Max-Planck-Straįe, Geb. 03, Geesthacht, D-21502
Germany
AB:
In extensional sedimentary basins it has been demonstrated that fine-grained sediments that do not appear deformed at the
mesoscale can carry a magnetic fabric consistent with the regional deformation. In this study, carried out on clays from
extensional basins in southern Italy, the magnetic lineation is tectonically controlled and oriented perpendicularly to the
main normal faults. As the origin of such magnetic lineation is not yet well understood, we present combination of magnetic
and textural analyses in order to unravel that phenomenon.
A combination of low-field, high-field and low-temperature measurements was used to distinguish the ferrimagnetic and
paramagnetic contribution to the magnetic susceptibility. The magnetic anisotropy of studied sediments is predominantly
carried by the paramagnetic phyllosilicates. Neutron texture analysis was used to evaluate the spatial distribution of the
chlorite basal planes. Results demonstrate that the orientation of the magnetic lineation is related to the spatial
distribution of phyllosilicate minerals, lying parallel to the common axis of differently oriented basal planes. Independent
of the chlorite basal planes distribution (from an axial symmetric to a girdle pattern in the bedding plane), magnetic
lineation is always parallel to the minimum axis of the mineral fabric ellipsoid.
In order to make a quantitative correlation between AMS and rock fabrics, the low- and high-field magnetic anisotropy (AMS,
HFA) were compared to the theoretical anisotropy calculated from the neutron texture goniometry measurements. Quantitative
correlation is presented in terms of the standard deviatoric susceptibility, k', and the difference shape factor, U,
expressing anisotropy degree and shape, respectively. The degrees of the theoretical anisotropy, AMS, and HFP correlate very
well implying nearly the same degree of anisotropy for all the employed methods.
DE: 8030 Microstructures
DE: 8109 Continental tectonics--extensional (0905)
DE: 1518 Magnetic fabrics and anisotropy
DE: 1540 Rock and mineral magnetism
DE: 1594 Instruments and techniques
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting