Physical properties of some Antarctic meteorites

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The intrinsic and bulk densities, porosities and ultrasonic-wave velocities (V_p and V_s) in three mutually perpendicular directions were measured in five antarctic meteorites (ordinary chondrites; ALH-77288,-77294,-78103,-78251 and MET-78003). V_p and V_s measurements were made at the room temperature and under one atmospheric pressure. Measured V_p and V_s values are fairly smaller than those expected from their mineral compositions except for ALH-77288. High porosity values (∿10%) of the samples, except for that (∿2%) of ALH-77288,are consistent with such low elastic-wave velocities. Degree of decrease in velocity is, however, larger than that expected from spherical pores. Thus, V_p and V_s of chondrites may be controlled by the crack porosity. Very low transmitting efficiency of the shear-wave may also support this view. Velocity anisotropy between transmitting directions is observed in almost all samples. The thermal diffusivity of four antarctic meteorites (ordinary chondrites; ALH-769,-77231,Y-74191 and -74371) was measured under the vacuum condition (below (10)^<-3> mmHg) in the temperature range of 100 to 500K. Thermal diffusivities of chondrites are also smaller than those expected from their mineral compositions and are ascribed to their high porosity values. The thermal diffusivities at 300K are 2.7∿5.0×(10)^<-7>m^2/s. The thermal diffusivity of ALH-77231 was measured for three mutually perpendicular directions. However, significant difference of thermal diffusivity between directions was not detected. We cannot find a correlation between the measured physical quantities and the petrologic types so far.
国立極地研究所の論文

Physical properties of some Antarctic meteorites

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