Abstract
Pallasite Seymchan contains three morphological types of olivine grains, which occur in a FeNi matrix and have rounded, angular, and fragmental shape. Sometimes the rounded grains form clusters. The texture and mineralogical features of the olivine cluster in pallasite Seymchan were studied by optical microscopy, EMPA, and SEM. The data obtained indicate an imposed impact event in the Seymchan history, which led to local melting and rounding of initially angular olivine grains, as well as to melting of adjacent regions of the host FeNi metal. Local impact melting reasonably explains the observed textures and the coexistence of three morphological types of olivine in the pallasite Seymchan. Configuration of the intergranular boundaries in the olivine cluster indicates the phenomenon of coalescence. The phosphate–metal–sulfide films decorating the intergranular boundaries in the cluster represent the binding medium necessary for the coalescence of the olivine melt drops in the FeNi melt. The texture of the films demonstrates a liquid immiscibility in phosphate–metal–troilite melt. The metal–troilite assemblage in the films differs in texture and chemical composition from that of ordinary chondrites.
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Notes
The main pallasite group is abbreviated as PMG (Pallasite Main Group).
The coalescence phenomenon is a merging of liquid drops of composition A in a liquid dispersed medium of another composition B. There is no direct contact between drops during coalescence. The required binding medium at the drop contact during coalescence is represented by liquid C having definite electrochemical properties. In particular, liquid C should wet the drop surface in the contact zone.
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ACKNOWLEDGMENTS
We are grateful to K.A. Lorentz for the preparation of pallasite Seymchan sample for study and K. Ryazantsev for the preparation of polished sections. Reviewers O.I. Yakovlev and V.A. Alekseev are thanked for the discussion of results and useful comments.
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Khisina, N.R., Badyukov, D.D., Senin, V.G. et al. Evidence for Local Shock Melting in Seymchan Meteorite. Geochem. Int. 58, 994–1003 (2020). https://doi.org/10.1134/S0016702920090049
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DOI: https://doi.org/10.1134/S0016702920090049