Physics
Scientific paper
Sep 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008epsc.conf..266t&link_type=abstract
European Planetary Science Congress 2008, Proceedings of the conference held 21-25 September, 2008 in Münster, Germany. Online a
Physics
Scientific paper
Most of the recent models for the formation of the Moon agree on a hot accretion scenario, leading to the formation of a deep magma ocean. Calculations have shown that after 95% crystallization of this ocean a ilmenite-rich cumulate layer is formed [1]. This ilmenite-rich layer is thought to be denser than the underlying cumulate pile, creating a gravitational instability. This instability can be the main driving force for a large-scale mantle overturn that formed the prelude to mare basalt generation [2]. The Ti-rich nature of many of the mare basalts is thought to be related to the dissolution of pre-existing ilmenites during ascent towards the surface [3]. Ilmenite (FeTiO3) is hence a crucial phase in the thermal and magmatic evolution of the Moon. To better constrain thermo-chemical convection models of these processes, physical properties of the phases involved (both minerals and melts) need to be known with sufficient accuracy. For both minerals and melts with lunar compositions, this is not the case at present. In the ilmenite case, studies of the variations in density as a function of pressure and temperature have only been done on terrestrial crystals. These have an oxidation state that differs from the lunar ilmenites (IW+2 to IW+6 for terrestrial samples and close to IW-2 for lunar sample). In addition, previous studies of terrestrial ilmenites have never measured ilmenite density at simultaneous high pressure and temperature ([4]). To start rectifying this situation we will collect in situ X-Ray diffraction patterns of synthetic Fe3+-free ilmenite at pressures and temperatures relevant to the lunar mantle, using a multi-anvil press at the GSC-CARS beamline of the Advanced Photon Source in Chicago, USA. Resulting densities will be compared with previously obtained data on a natural terrestrial ilmenite including minor concentrations of … (Al or Cr or both) [5] in order to see the compositional effect on the volume and the compressibility of the crystals. The targeted pressure range is 0-5 GPa to cover the complete lunar pressure range, and temperatures cover 100 degree steps between room temperature and at least 1273 K. The program EXPgui is used to constrain the unit cell volume of the ilmenite crystals (by determining a and c axes of the unit cell). From our results a pressure-volumetemperature equation of state for ilmenite will be calculated. These data will help to constrain numerical lunar convection simulations and will help quantitatively constrain mare basalt formation models. . This work was performed at GeoSoilEnviroCARS (Sector 13), Advanced Photon Source (APS), Argonne National Laboratory. GeoSoilEnviroCARS is supported by the National Science Foundation - Earth Sciences (EAR-0622171) and Department of Energy - Geosciences (DE-FG02-94ER14466). Use of the Advanced Photon Source was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02- 06CH11357 References [1] Snyder et al. (1997) GCA 61, 2731. [2] Circone and Agee (1996) GCA 60, 2709. [3] Van Orman and Grove (2000) Meteorit. Planet. Sci., 35, 738. [4] Weshler and Prewitt (1984) AM 69, 176. [5] Tronche et al. (2008) LPSC 39th abstract 1551.
Chen Bohui
de Vries Jellie
Gao Lan
Klemme Stephan
Li Jiying
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