Image-furnace experiments on the differentiation process of basaltic achondites

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Dynamic crystallization experiments have been performed on a synthetic analog of basaltic achondrite at 0.1 MPa total pressure in a floating-zone image fumace. The growth conditions of artificial basalts are as follows : travel rate 0.5-3.0mm/h, rotation 0-30rpm, gas flow CO_2 : 300 ; H_2 : 15 ; N_2 : 400ml/min. The synthetic basalts are cylindrical (6-8mm diam.by50-80mm length), and dark in color. Textures produced are subophitic to varioritic, which are representative textures observed in eucrites. Chemical compositions of pigeonite and plagioclase are very similar to those of the Pasamonte eucrite which is one of the most representative unequilibrated basaltic achondrite.Shock recovery experiments between 11 and 84 GPa were performed on the synthetic eucrites to elucidate the residual shock effects on basaltic meteorites. Petrographic examination of experimetally shocked basalts showed solid-state effects in the form of increasing disaggregation and deformation of component minerals and melting with increasing shock pressure. Only irregular grain fracturing was observed at 11 GPa. Maskelynization of calcic plagioclase begins at 27GPa. Mosaicism of chino-pyroxene was extensive at 46 GPa. Melting occurred along microfaults at 27 and 46 GPa. Extensive overall melting was observed at 84 GPa. The shock-metamorphosed basalts can be divided into four classes whose distinctive features are : Class 1 (P<20 GPa) , grains are irregularly fractured. Class 2 (20<P<40 GPa) plagioclase is converted to isotropic maskelynite. Class 3 (40<P<60 GPa) , clinopyroxene show mosaic extinction. Class 4 (P>60 GPa) , plagioclase and clinopyroxene have been melted.