In situ Observation of ilmenite‐perovskite phase transition in MgSiO₃ using synchrotron radiation

Abstract

Abstract. In situ observations of the ilmenite-perovskite transition in MgSiO3 were carried out in a multianvil high-pressure apparatus interfaced with synchrotron radiation. The phase boundary between ilmenite and perovskite in the temperature range of 1300-1600 K was determined to be P (GPa) = 28.4(ñ0. Under these circumstances, information on the stability field of the perovskite phase in the MgSiO3 system would also provide some insight into the structure of the mantle.4High-pressure and high-temperature X-ray diffraction measurements using synchrotron radiation are very advantageous for phase equilibrium studies compared to the conventional quenching method, because in this method both the phase present and the pressure value are determined simultaneously. Kato et al. [ 1995] first tried to determine the ilmenite-perovskite phase boundary in MgSiO3 by in situ measurements to 25 GPa and 1473 K, in a double-staged multianvil system interfaced to synchrotron radiation. Owing to considerable temperature fluctuations during measurements and associated large uncertainties in pressure determination, however, it was not possible to reliably define phase boundary from their results. Recently we have developed a multianvil assembly for X-ray diffraction measurements, which provides the stable conditions to 25 GPa and 2000 K for a long duration runs. The purpose of the present paper is to report our results on the ilmenite-perovskite transition obtained in this multianvil facility. (Fig. 1) consists of octahedral pressure medium made of precast Cr203-doped MgO. A cylindrical LaCrO3-furnace inside a composite thermal insulator of ZrO2-and MgO-sleeves was used as a heater. The sample was put into a tantalum chamber. Temperatures were measured by a W3%Re/W25%Re thermocouple, the junction of which was placed on the outside of the sample chamber in the center of the furnace. No correction was made for the effect of pressure on thermocouple emf. A more important correction arose from the temperature distribution in the sample because the pressure value determined via the equation of state of gold is quite sensitive to temperature. In order to decrease the temperature gradient throughout the sample, we used the 835 Experimental procedure

Absence of density crossover between basalt and peridotite in the cold slabs passing through 660 km discontinuity

“…0094-8276/04/2004GL021306 reliable EOS. Au, Pt, and MgO are typically used for in situ high-pressure estimations in multianvil apparatus [e.g., Ono et al, 2001;Hirose et al, 2001]. The calculated pressure differences between different EOS of Au [Jamieson et al, 1982;Anderson et al, 1989;Shim et al, 2002] may exceed 2.5 GPa at high temperatures.…”

Phase relations in the system MgO‐FeO‐SiO2 to 50 GPa and 2000°C: An application of experimental techniques using multianvil apparatus with sintered diamond anvils

“…Experiments below 30 GPa were carried out with another apparatus installed at Tokyo Institute of Technology (Sakura-2500), and pressures were determined from a relationship between the applied press load and the generated pressure. The relationship was calibrated in advance using the ilmenite-Pv phase transition in MgSiO 3 [Ono et al, 2001]. Eight SD cubes of 14.0 mm with truncated edge lengths of 2.0 mm were used as the second stage anvils (SUMIDIA WD-700; Sumitomo Electric Industries, Co., Ltd).…”

Peridotite melting and mineral–melt partitioning of major and minor elements at 22–24.5 GPa

“…forsterite^wadsleyite, wadsleyite^ringwoodite and ilmenite^perovskite [15,16], with reference to the Jamieson et al [17] equation of state for gold. An additional calibration check point at 26 GPa was provided by the compositions of coexisting garnet and perovskite in the enstatite^pyrope system [18].…”