Evaporation Features of the Melts of Ca–Al–Inclusions in Chondrites: Experimental Data and Their Implications
摘要
The paper presents experimental results on the evaporation of the main types (A and B) of Ca–Al inclusions of chondrites in a Knudsen tungsten cell in the temperature range of 1000–2400°C. A peculiarity of the evaporation of the inclusions is that the silicon component is preserved in the residual melt to high temperatures exceeding 2200°C. At the same time, magnesium oxide completely evaporates from the melt, which leads to a decrease in the spinel content and even its disappearance during the crystallization of the residual melt at 2000°C. Magnesium evaporation leads, in turn, to an increase in the Al2O3 content in the melt and, accordingly, to an increase in the content of gehlenite in melilite during its crystallization, as is observed in the high-temperature rims of subtype B1 inclusions. Experiments have also shown that the high-temperature evaporation of Ca–Al inclusions occurs in an oxygen-rich atmosphere compared to carbonaceous chondrite matter. In this regard, it is assumed that the condensation of the first mineral products of the inclusions occurred in the oxygen-rich atmosphere of the star (O-rich AGB) outside the protosolar system.