The variations of chemical composition and features of the distribution of rare elements in chondrites of fragments of the Chelyabinsk meteorite

Abstract

Research subject. This paper reports the results of a series of experiments carried out to study the mineral and geoche mical features of 10 Chelyabinsk meteorite fragments. In addition, these fragments were analysed in terms of their chemical composition.Materials and methods. The fragments under study were represented by light-grey granular rocks of the chondrite structure having either isometric or elongated shape. Their surface was largely covered with a black-brownish fusion crust with a thickness of approximately 1 mm. The petrogenic components of the meteorite and the content of rare elements were studied using the methods of chemical silicate analysis and ICP MS respectively. All measurements were carried out using an Agilent 7700x quadrupole mass spectrometer produced by the Agilent Technologies company. The composition of sulphides and metal particles was determined by electron probe microanalysis (PCMA) usinga JXA8200 microanalyzer (Jeol, Japan).Results. The chondri and cementing matrix are found to be primarily composed of olivine and orthopyroxene. The inter-chondruli matrixis shown to consist of a pyroxene-olivine aggregate with inclusions of plagioclase, apatite, fused glass and ore minerals (tenite, kamasite, troilite, rarely pyrrhotine, pentlandite, single grains of chromite and ilmenite). The concentration of the majority of rare and ore elements in the Chelyabinsk meteorite samples is established to be close to their average values for LL-chondrite. When normalizing to coaly chondrite, the substance of the meteorite fragments and the average LL-chondrite were closest to coaly chondrite in terms of the content of siderophile elements (Mo, Ni, Cr, Co, V and Cu). At the same time, the studied meteorite fragments are shown to contain a significantly lower (nearly by one order) concentration of chalcophyle elements (Zn, Pb and Sn) with regard to С1.Conclusion. A comparison of the obtained and published analytical data (ICP MS) has allowed us to make a conclusion on the geochemical heterogeneity of different meteorite remainst hat were scattered over a wide area of the Chelyabinsk Region. The acquired evidence suggests the differentiation of meteorite substance at early stages of the formation of terrestrial planets, which is likely to have occurred due to impact processes.