Curie temperatures of synthetic titanomagnetites in the Fe-Ti-O system

• Verfasst von: Lattard, Dominique [VerfasserIn]
• Verfasst von: Engelmann, Ralf [VerfasserIn]
• Verfasst von: Kontny, Agnes [VerfasserIn]
• Verfasst von: Sauerzapf, Ursula [VerfasserIn]
• Titel: Curie temperatures of synthetic titanomagnetites in the Fe-Ti-O system
• Titelzusatz: effects of composition, crystal chemistry, and thermomagnetic methods
• Verf.angabe: Dominique Lattard, Ralf Engelmann, Agnes Kontny, Ursula Sauerzapf
• E-Jahr: 2006
• Jahr: 20 December 2006
• Umfang: 18 S.
• Fussnoten: Gesehen am 06.10.2020
• Titel Quelle: Enthalten in: Journal of geophysical research. Solid earth
• Ort Quelle: Hoboken, NJ : Wiley, 2013
• Jahr Quelle: 2006
• Band/Heft Quelle: 111(2006,B12) Artikel-Nummer B12S28, 18 Seiten
• ISSN Quelle: 2169-9356
• DOI: doi:10.1029/2006JB004591
• Datenträger: Online-Ressource
• Sprache: eng
• Sach-SW: Curie temperature
• Sach-SW: magnetic susceptibility
• Sach-SW: titanomagnetite
• K10plus-PPN: 1734774576

Abstract

The present study is aimed at improving the calibration of the compositional dependence of the Curie temperature (TC) of titanomagnetite (Tmt) on the basis of temperature-dependent magnetic susceptibility (χ-T) curves measured on synthetic Tmts in the Fe-Ti-O system. In order to assess the possible influence of high-temperature cation vacancies onto the TC values, we have synthesized two types of assemblages in subsolidus conditions at 1 bar, 1100°C and 1300°C, under controlled oxygen fugacity conditions. Tmts synthesized in equilibrium with ilmenite-hematitess (Ilmss) are expected to have the highest vacancy concentrations, those in equilibrium with wüstite (Wus) the lowest. The composition and homogeneity of the synthetic Tmts were carefully checked with a scanning electron microscope (SEM) and an electron microprobe (EMP). TC was determined from χ-T curves using a kappabridge and, for comparison, from Ms-T curves measured with a variable field translation balance. Our data set shows systematically higher TC values for Tmt coexisting with Ilmss than for Tmt coexisting with Wus. Most χ-T curves are nonreversible, whereby the largest ΔTC (40 K) concern Tmt(+Ilmss) of intermediate compositions synthesized at 1300°C. Nonreversibility is interpreted as reflecting cation reordering in Tmt during the high-temperature χ-T measurements. TC values obtained from Ms-T curves are higher than those obtained from the χ-T curves, whereby the difference regularly increases (up to 40 K) with increasing Ti content, up to XUsp = 0.6. Our new calibration curves are suitable to retrieve Tmt compositions in basalts that were rapidly cooled and not oxidized by deuteric or hydrothermal fluids.