Experimental constraints on the magnetic mineralogy of Fe-Ti oxides in basalts from HSDP-2 bore hole
Zusammenfassung der Projektergebnisse
The present study contributes to a better understanding of the rock magnetic properties of basaltic rocks, m particular on Hawaii The main goal of the project was to improve the correlations between the magnetic properties and the chemical-structural characteristics of two iron-tiranium oxide minerals, titanomagnetite and Ilmenite-hematite, which are the major earners of rock magnetism m basalts We have determined characteristic magnetic transition temperatures, such as the Curie temperature, the N6el temperature, the spin glass temperature and the blocking temperature, as a function of the chemical composition of the two minerals The basis for this investigation were temperature-dependent measurements of the magnetic susceptibility, the saturation magnetization, the remanent magnetization, as well as hysteresis measurements at different temperatures The samples used were polycrystalline assemblages of iron-titanium oxide phases synthesized either in the Fe-Ti-0 system or in the more complex Fe-Ti-AI-Mg-O system To obtain a large variety of mineral compositions, the syntheses were performed under a broad range of temperatures (1050*0 to 1300''C) and oxygen fugacity values To control the concentration of cation vacancies in titanomagnetite we synthesized not only single phase samples but also titanomagnetite-wustite and titanomagnetite-ilmenite samples We took great care to precisely characterize the synthetic samples, regarding their textures, the chemical compositions of the phases and their homogeneity within the crystals and over the whole sample In particular, we extensively used analytical high-resolution techniques (e g scanning electron microscope and electron microprobe) For titanomagnetite in the Fe-Ti-0 system, we have shown that there are well-defined correlations between the Cuiee temperature (Tc) and the chemical composition, with significant differences between the higher Tc values obtained from Tmt synthesized at ISOO'C in equilibrium with llmenite and the lower values for those in equilibrium with wustite These differences reflect the positive correlation between Tc and the concentration of cation vacancies in titanomagnetite The regression curve for the samples synthesized at 1100°C IS the most relevant for basaltic parageneses, provided they were rapidly cooled and not oxidized by deuteric or hydrothermal fluids Our data set reveals that the Tc-values of titanomagnetite are sensitive to the determination method Values obtained from temperature-dependent saturation magnetization measurements are systematically higher (by up to 40 K) than those obtained from temperature-dependent susceptibility measurements (x-T curves) Almost all x-T curves show a distinct irreversibility, which is not necessarily related to oxidation, but rather to changes in the cation distribution in titanomagnetite during the measurements Because natural titanomagnetites generally contain a few weight percent of Aluminum and Magnesium, we have assessed the influence of these elements on the Curie temperature As expected, Al- and Mg-beanng titanomagnetites have lower Tc values than their equivalents in the Fe-Ti-0 system We have developed a numerical model to estimate the TI content of titanomagnetites from their Cune temperature The present study also brings new results on the complex magnetic behaviour of Ti-rich llmenites (Ti > 0 7 cpfu) at low temperatures (T < 200 K) in the Fe-Ti-0 system as well as in the Fe-Ti-AI-Mg-0 system We have determined characteristic transition temperatures (Curie, Neel, spin glass and blocking temperature) of this phase as a function of composition These basis data are needed to better identify ilmenite-hematite solid solutions in complex natural Fe-Ti oxide assemblages, when conventional mineralogical methods fail, e g m case of very fine-grained minerals.
Projektbezogene Publikationen (Auswahl)
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(2004) Curie point variation in the system magnetite-ulvöspinel Towards an improved calibration. Lithos, 73, p 31, 10th International Symposium on Experimental Mineralogy, Petrology and Geochemistry, Frankfurt, Germany
Engelmann R, Sauerzapf U, Kontny A, Lattard D
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(2004) Low temperature magnetometry of synthetic titanomagnetite-ilmenohematite. Beihefte zum European Journal of Mineralogy, 16, p 33, 82th annual meeting of the DMG, Karlsruhe, Germany
Engelmann R, Kontny A, Frederichs Th, Sauerzapf U, Lattard D
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(2004) Magnetic properties of the magnetite-ulvoespinel solid solution Magnetic susceptibility measurements. EOS Transactions AGU 85 (47), Fall Meeting Supplemental, Abstract GP23A-0164, AGU Fall meeting 2004, San Francisco, USA
Engelmann R, Kontny A, Lattard D, Sauerzapf U
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(2005) Experimental constraints on the magnetic mineralogy of Fe-Ti oxides in basalts from the HSDP-2 borehole (LA 1164/5). IODP and ICDP colloquium, Potsdam Germany
Lattard D, Engelmann R, Kontny A
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(2005) High-temperature non-stoichiometry in titanomagnetites - significance for petrology and rock magnetism. EOS Transactions AGU 86 (52), Fall Meeting Supplemental, Abstract V31B-0609, AGU Fall meeting 2005, San Francisco, USA
Sauerzapf U, Engelmann R, Lattard D, Kontny A, van Aken PA, Ullrich A
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(2005) Irreversible Kurvenverläufe bei temperaturabhängigen Suszeptibilitätsmessungen an synthetischen Titanomagnetiten. Beihefte zum European Journal of Mineralogy, 17, p 35, 83th annual meeting of the DMG, Aachen, Germany
Engelmann R, Lattard D, Kontny A
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(2005) Is the Curie temperature of titanomagnetite dependent on its high temperature non-stoichiometry? New experimental constraints for the Fe-Ti-0 system. 10th Scientific Assembly of the IAGA, Toulouse, France
Sauerzapf U, Engelmann R, Lattard D, van Aken PA, Kontny A, Ullrich A
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(2005) Low temperature magnetometry of ilmenite-hematite solid solution. 10th Scientific Assembly of the IAGA, Toulouse, France
Engelmann R, Kontny A, Frederichs Th, Lattard D
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(2005) Nano-exolutions in quenched synthetic Tibearing wustite. EOS Transactions AGU 86 (52), Fall Meeting Supplemental, Abstract GP41A- 0862, AGU Fall meeting 2005, San Francisco, USA
Engelmann R, Sauerzapf U, Wirth R, Lattard D
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(2005) Nanoscale titanomagnetite exsolutions in quenched synthetic wustite Insights from transmission electron microscopy (TEM). Beihefte zum European Journal of Mineralogy, 17, p 116, 83th annual meeting of the DMG, Aachen, Germany
Sauerzapf U, Engelmann R, Wirth R, Lattard D
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(2005) Nonreversibility of high-temperature χ-T curves of synthetic titanomagnetites. EOS Transactions AGU 86 (52), Fall Meeting Supplemental, Abstract GP13A-0047, AGU Fall meeting 2005, San Francisco, USA
Lattard D, Engelmann R, Kontny A
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(2006) Curie temperatures of synthetic titanomagnetites in the Fe-Ti-O system effects of composition, crystal chemistry and thermomagnetic methods.J Geophys Res, 111, 812828
Lattard D, Engelmann R, Kontny A, Sauerzapf U
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(2006) Low temperature magnetometry of the ilmenite-hematite solid solution (LA 1164/5). IODP and ICDP colloquium, Greifswald, Germany
Engelmann R, Kontny A, Lattard D, Frederichs Th
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(2007) Compositional dependence of the Curie temperature in titanomagnetite - an experimental study. Frontiers in Mineral Science, Cambridge, UK, Programme and abstracts, 182
Lattard D, Engelmann R, Kontny A
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(2007) Curie temperatures of synthetic Aluminium and Magnesium bearing titanomagnetites. IODP and ICDP colloquium, Potsdam, Germany
Lattard D, Engelmann R, Kontny A
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(2007) Identification of magnetic Fe-Ti oxides in marine sediments by electron backscatter diffraction in scanning electron microscopy. Geophys J Int, 170, 545-555
Franke C, Pennock GM, Drury MR, Engelmann R, Lattard D, Garming JFL, von Dobeneck T, Dekkers MJ
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(2008) Bestimmung diagnostischer magnetischer Übergangstemperaturen von synthetischen Titanomagnetiten und Ilmenit-Hämatit-Mischkristallen. Dissertation, Fakultät für Chemie und Geowissenschaften, Universität Heidelberg, 265 pp
Engelmann R
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(2008) The titanomagnetite-ilmenite equilibrium new experimental data and thermo-oxybarometric application to the crystallisation of basic to intermediate rocks. J Petrol, 49, 1161-1185
Sauerzapf U, Lattard D, Burchard M, Engelmann R
