GEOCHEMICAL AND MINEROLOGIC STUDY OF A STONY METEORITE FROM THE VICINITY OF THE VILLAGE OF SEVRYUKOVO |
| |
| Abstract: | In studying the conditions of formation of stony meteorites, we assume that 1) they are fragments of asteroids fallen to the surface of the earth. During their flight through the atmosphere, the meteorites develop a melted surface layer but their texture and mineralogic composition remain unchanged. 2) According to V. M. Goldschmidt, stone meteorites crystallize in a lesser gravity field than that of the earth, which is the reason for their chondritic texture and high porosity (about 4%). 3) Meteorites were formed in a medium with a deficiency of free oxygen. As a result, part of their iron and nickel was segregated as native metal; in addition, lawrencite and oldhamite, sulfides typical of meteorites, were formed. We identify three stages of meteorite formation: magmatic, pneumatolytic, and hydrothermal. The interval 1450-850°C. corresponds to the magmatic stage at which a silicate phase and native iron with nickel were formed. As a result of thermal dissociation of water and because of the deficiency of oxygen required for a complete oxidation of metals and carbon, in the gaseous phase, free oxygen and H2O were absent and the phase consisted probably of H2, CH4, CO2, and CO. The temperature interval 750-500°C. corresponds to the pneumatolytic phase. Here, H2S, CH4, CO2, and CO were the principal agents of the gaseous phase. CH4 was formed in a high temperature reaction between hydrogen and elementary carbon. As the temperature dropped to 750°C., electrolytic dissociation of H2O rendered possible the formation of sulfides, especially of troilite. Mineralization at the hydrothermal stage with a temperature interval of 400 to 300°C. has been observed only in carbon meteorites with a considerable graphitic carbon content. Here, a small portion of the ferrous iron is oxidized to the ferric, in the presence of CO2 and at a temperature of 450° to 500°C.; the iron sulfide so formed is represented by pyrrhotite. Simultaneously, colored silicates are chloritized, with a separation of CaCO3.—Auth. English summ. |
| |
| Keywords: | |
|
|
