Host: The Mineralogical Society of Japan
Density of silicate melt at high pressure is one of the most important properties to understand magma migration in the planetary interior. Because of experimental difficulties, the density of magma at high pressure is poorly known. Katayama (1996) recently developed a new in situ density measurement method based on the density dependency of X-ray absorption in the sample. In this study we made, as a first step, preliminary measurements of the density of basaltic glass by the absorption method.Experimental TechniquesMORB composition (SiO2-Al2O3-FeO-MgO-CaO-Na2O) glass was prepeared by cuenching by falling into water the melt heated at 1603K. the glass was grided into and used as starting material. X-ray absorption method was fallowing.
I/I0 = exp(-mrt)
I0 is intensity of incident beam, I is the intensity of the transmitted beam. m is the mass absorption coefficient, r is the density of the sample, and t is the X-ray path lengh. If t and m were known, We got the density of the sample, by mesuring I and I0. In order to know t, we used a single diamond cyrinder as sample cupsele, which is less absorbed and less deformed. t is as following t = 2*(r2-x2)1/2 r is hemisphere of cyrinder inner, and x is distance from center of the capsule.
For generation of high pressure and high temprature, We used cubic-type multi-anvil apparatus (SMAP180) installed on the beamline (BL22XU) at Spring-8, Japan. Tungsten carbide anvils with a square center flat of 6*6 mm2 were used. Boron-epoxy pressure medium was used. Monocro X-ray was used, whose energy was 25 keV and whose size is 0.1*0.1 mm2 by 2 slits, Experiment were up to 5 GP at 300 K and heated up to 773K . And down to 1atm at 773KResults and DiscussionUp to 5GPa at 300 K, the density was increasingAt 500 c ,density of basalt glass was densified by 20 %At down path the density was decreasing. we caculated bulk modulus of basaltic glass K=46(4) (GPa), when K'=4.
