In situ density measurements of basaltic melt at high pressure by X-ray absorption method

Density of silicate melt at high pressure is one of the most important properties to understand magma migration in the planetary interior. However, because of experimental difficulties, the density of magma at high pressure is poorly known. Katayama et al. (1996) recently developed a new in site density measurement method for metallic melts, based on the density dependency of X-ray absorption in the sample. In this study, we tried to measure the density of basaltic melt by this absorption method.When X-ray is transmitted to the sample, the intensity of the transmitted X-ray beam (I) is expressed as follows; I= I0 exp(-mrt), where I0 is the intensity of incident X-ray beam, m is the mass absorption coefficient, r is the density of the sample, and t is the thickness of the sample. If t and m are known, we can determine the density of the sample by measuring I0 and I. This is the principle of the absorption method for density measurement. In this study, in order to determine t, we used a single crystalline diamond cylinder as a sample capsule, which shows less absorbed and less deformed. So t (thickness of the sample at the point x) is expressed as follows; t = 2*(R2-x2)1/2, R is the inner radius of cylinder, and x is distance from center of the capsule.Experiments were made at the beamline (BL22XU) of Spring-8. For generation of high pressure and high temperature, we used DIA-type cubic anvil apparatus (SMAP180) there. We used tungsten carbide anvils with the edge-length of 6 mm. The energy of monochromatic X-ray beam was 25 keV and the beam size was reduced to 0.1*0.1 mm2 by 2 slits. Starting material was a glass with the MORB composition (SiO2-Al2O3-FeO-MgO-CaO-Na2O). We measured the density from 1 to 5 GPa at from 300 K to 1873K. Details of conclusion and discussion will be reported the day.