[PPS06-P12] Reproduce of I type cosmic spherules from iron meteorite powder
キーワード：Micrometeorite、Iron meteorite、I type cosmic spherules、Quench、Atmospheric entry
Micrometeorites (MMs) are extraterrestrial dust particles falling on the earth (Genge MJ and Engrand C, 2008). Fragile micrometeoroids were heated and melted to form small particles during their atmospheric entry (Genge MJ, 2016). And the completely melted MMs are called as cosmic spherules. It can be an extremely valuable sample for us to look into the asteroids and comets providing interplanetary dust particles.
Cosmic spherules show substantial diversity in textures, compositions and morphology which results from the heating process. Generally, the iron-rich spherules (I-type), one group of the cosmic spherules, mainly contain iron oxides wüstite and magnetite, and also frequently involving Ni-rich metal bead that may lost and remain a single large spherical void inside the spherules (Genge MJ, 2016).
In order to reproduce I type cosmic spherules, in this study, we carried out rapid heating and quenching experiments on powders from iron meteorite Canyon Diablo by falling through the high temperature furnace with controlled gas flow (Isobe and Gondo, 2013). Starting material particles are a mixture of kamacite and taenite and trace of mineral schreibersite. Oxygen fugacity was controlled to FMQ +1.5 log unit. Maximum temperature of the particles was approximately 1600°C for about 0.5 seconds. Run products are retrieved from the bottom of the furnace tube.
Run products from iron meteorite particles exceedingly resemble the textures of I type cosmic spherules. Most of run products show rounded to subrounded outer shape and smooth surface which means that these particles were completely to partially melted. Surface tension of the iron and iron oxide melt conduce to the spherical shape in completely melted ones. Oxidized iron forms magnetite crust covering the molten spherules from one side to opposite partly. In some spherules that are partially melted, small peaks can be seen on the surface.
In run products, chemical compositions of oxide crust and metal beads are differentiated from starting material. In starting material, the Ni content range from 1-12 % and most of them occur between 6-8 % in mass composition. The Ni content of most of metal beads are at around 7 to 8 %. Ni-rich taenite crystals, which Ni content reach 33-57 %, also occur. While in iron oxide, it range from Ni free to 16 %, most of them spread between 0-2 %. The Ni content in the iron oxide can reach up to 42 % in Ni concentrated vein. Oxidation conditions and fractionation processes of Fe and Ni can be discussed from textures and compositions of I type cosmic spherules based on the results of this study.
Cosmic spherules show substantial diversity in textures, compositions and morphology which results from the heating process. Generally, the iron-rich spherules (I-type), one group of the cosmic spherules, mainly contain iron oxides wüstite and magnetite, and also frequently involving Ni-rich metal bead that may lost and remain a single large spherical void inside the spherules (Genge MJ, 2016).
In order to reproduce I type cosmic spherules, in this study, we carried out rapid heating and quenching experiments on powders from iron meteorite Canyon Diablo by falling through the high temperature furnace with controlled gas flow (Isobe and Gondo, 2013). Starting material particles are a mixture of kamacite and taenite and trace of mineral schreibersite. Oxygen fugacity was controlled to FMQ +1.5 log unit. Maximum temperature of the particles was approximately 1600°C for about 0.5 seconds. Run products are retrieved from the bottom of the furnace tube.
Run products from iron meteorite particles exceedingly resemble the textures of I type cosmic spherules. Most of run products show rounded to subrounded outer shape and smooth surface which means that these particles were completely to partially melted. Surface tension of the iron and iron oxide melt conduce to the spherical shape in completely melted ones. Oxidized iron forms magnetite crust covering the molten spherules from one side to opposite partly. In some spherules that are partially melted, small peaks can be seen on the surface.
In run products, chemical compositions of oxide crust and metal beads are differentiated from starting material. In starting material, the Ni content range from 1-12 % and most of them occur between 6-8 % in mass composition. The Ni content of most of metal beads are at around 7 to 8 %. Ni-rich taenite crystals, which Ni content reach 33-57 %, also occur. While in iron oxide, it range from Ni free to 16 %, most of them spread between 0-2 %. The Ni content in the iron oxide can reach up to 42 % in Ni concentrated vein. Oxidation conditions and fractionation processes of Fe and Ni can be discussed from textures and compositions of I type cosmic spherules based on the results of this study.