EVALUATION OF THERMAL METAMORPHISM TEMPERATURE OF EQUILIBRATED ORDINARY CHONDRITES

Abstract

The article provides an evaluation of thermal metamorphism temperatures on chondrite parent bodies using an olivine-Сr spinel geothermometer. To calculate temperatures, the results of EPMA analysis of the major and trace elements in olivine and Cr spinel of Kargapole, Orlovka, Saratov, Elenovka, Buschhof, Bjurböle and Knyahinya meteorites are used. The obtained temperatures are consistent with the onion-shell model of the planetesimal structure, in which the most metamorphosed chondrites are closer to the heating source (Buschhof, L6-734 °C), meteorites of the 5th petrologic type (p.t.) occupied an intermediate position (Orlovka, H5 – 687 °С; Elenovka, L5 – 691 °С; Knyaginya, LL5 – 700 °C), and the chondrites of the 4th p.t. were closer to the surface (Kargapole, H4 – 691 °C; Saratov, L4 – 670 °С; Bjurböle, LL4 – 682 °C). The Kargapole and Saratov meteorites are characterized by evaluation of Mg and Fe equilibrium temperatures that disagree with the onion-shell model, which can be explained by the individual history of the meteorite (for example, impact metamorphism, slow and prolonged heating).

Keywords

• meteorite
• equilibrated ordinary chondrite
• microprobe analysis
• cr spinel
• olivine
• geothermometry