Abstract
The polymictic breccias, extremely rare mantle conglomerates being the fragments of rocks and large mantle minerals cemented with fine-grained mass have been long provoking interest of petrologists worldwide. This work provides a comparative analysis of two xenoliths of polymictic rocks from kimberlite pipes of different age and productivity occurring in the Siberian craton. The similarity of the chemical composition of some minerals of polymictic breccias from kimberlites within different parts of the Siberian craton assumes possible formation of these minerals caused by the same factors in the prekimberlite period of these parts of the lithospheric mantle. A wide range of compositions and chaotic zoning of minerals, the presence of exsolution textures in orthopyroxene, ilmenite, sulfide, and kelyphite rims on garnet suggest that the fragments of the studied xenoliths are unbalanced. Sample SH18/20 is the first polymictic breccia showing asthenospheric melt-fluids sampling shallow depths of the spinel facies.
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