HR: 0830h
AN: GP11B-0257    [PDF]
TI: Low-Temperature Magnetic Behavior: Diagnostic for the Interpretation of Magnetic Mineralogy of Basalt?
AU: * Kontny, A
EM: agnes.kontny@urz.uni-heidelberg.de
AF: Geologisch-Palaeontologisches Institut, Ruprecht-Karls University, Im Neuenheimer Feld 234, Heidelberg, D-69120 Germany
AU: Vahle, C
AF: Geologisch-Palaeontologisches Institut, Ruprecht-Karls University, Im Neuenheimer Feld 234, Heidelberg, D-69120 Germany
AU: Frederichs, T
AF: Marine Geophysik, University of Bremen, Postfach 330440, Bremen, D-28334 Germany
AU: Lattard, D
AF: Mineralogisches Institut, Ruprecht-Karls University, Im Neuenheimer Feld 236, Heidelberg, D-69120 Germany
AU: Engelmann, R
AF: Mineralogisches Institut, Ruprecht-Karls University, Im Neuenheimer Feld 236, Heidelberg, D-69120 Germany
AB: Basalts are the most important rocks carrying magnetic anomalies on Earth and the understanding of the magnetic properties, which are dominated by titanomagnetites (tmt), is a main target in rock magnetism. Depending on different parameters like temperature and fugacity that are controlled by extrusion conditions and chemical composition of the magma, different paragenesis and textures as well as compositional types of tmt occur, which create a variety of different rock magnetic behaviors. A detailed study on Hawaiian subaerial and submarine lava flows (Kontny et al. 2003) revealed different groups of magnetic behavior related to varying degrees of oxidation and subsolidus reactions (subaerial flows) and quenching histories (submarine flows). But not only homogeneous, unexsolved tmt compared to exsolved and oxidized tmt create different magnetic properties but also some basalts with homogeneous tmt. Some of these basalts show a complex behavior of low-temperature initial susceptibility. This feature seems to correlate with variations in room temperature hysteresis parameters and AF demagnetization behavior and therefore its understanding may be diagnostic for rock magnetic interpretations. The complex behavior indicates a superposition of different Fe-bearing phases like Ti-rich hemo-ilmenite, pyrrhotite and chromian spinel which all show low-temperature transitions and were observed in different amounts and combinations together with tmt in the Hawaiian basalts. A combination of low-temperature (2 to 280 K) initial susceptibility, remanence and hysteresis measurements along with BSE-images and microprobe analyses will be presented for natural basalts. For a better understanding of this low-temperature behavior, data from synthetic equivalents consisting of tmt and ilmenite will be discussed in relation to natural samples. Kontny et al. (2003) G3 Geochemistry Geophysics Geosystems, 4 (1)
DE: 1519 Magnetic mineralogy and petrology
DE: 1540 Rock and mineral magnetism
DE: 3929 NMR, Mossbauer spectroscopy, and other magnetic techniques
DE: 3954 X ray, neutron, and electron spectroscopy and diffraction
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting