Phenomena of assimilation and hybridism in alkaline rocks of Tagoba-Sobak
Abstract
From field observations and the study of the stone material at our disposal, it follows that in the magmatic process of formation of alkaline rocks of Tagoba-Sobak, three phases are established, replacing each other in the usual sequence: 1) the intrusive phase, represented by syenites, 2) vein - aplite and albitite, 3) phase of intensive manifestation of the process of pneumatolysis, completing magmatic activity. The last phase is associated with the formation of sodalite, cancrinite and other pegmatites and the automorphic change of rocks of early phases, expressed in intensive metasomatic replacement of primary minerals and leading to the formation of sodalite- and cancrinite- nepheline syenites. The change in the chemical composition of magma from early to late phases was expressed: 1) in the depletion of ferruginous-magnesian components: 2) in the enrichment of the magmatic melt with sodium and silicic acid and 3) in the concentration of mineralizers - F, CL, etc. By comparing the mineralogical composition of various xenoliths, on the one hand, and the mineralogical composition of xenoliths with that of typical biotite-nepheline syenites, on the other, one can be convinced that between the extreme member of the xenolith (vesuvian hybrid) and the biotite-nepheline syenite there is a connection and there are gradual transitions of one rock type to another (see article).
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