Automorficzne wrostki tytanonośnych magnetytów w piroksenach skał masywu suwalskiego

Abstract

AUTOMORPHIC INTERGROWTHS OF TITANIFEROUS MAGNETITES IN PYROXENES OF THE SUWAŁKI ROCK MASSIFSummary Intergrowths of titaniferous magnetites, characterized by highly interesting exsolution structures of solid solutions are found to occur in pyroxenes of norites within the Suwałki massif. The size of these automorphic intergrowths ranges from 36 m to 560 m. They stick in the pyroxenes, 2-3 mm in diameter. The microscope examinations of these structures allow us to present the development of the intergrowths as follows. During the crystallization of magma the pyroxenes included the automorphic crystals of titanomagnetite, with a considerable admixture of Mg and Al. With a decrease in temperature the tolerance of crystal lattice of titanomagnetite decreased, too, this leading to a differentiation in spinel lenses (hercynite-pleonaste) and in ulvØspinel lattice, according to magnetite faces (100). Suacessively, the change in oxidizing conditions led also to the ilmenitization of ulvØspinel and to the formation, according to magnetite faces (111), of various ilmenite lamellae, which may have later concentrated into one crystal. A similar process of rearrangement concerned the fine spinel lenses, which grouped, at the magnetite-ilmenite contact, in the form of lamellae. The further decrease in temperarture was responsible for a fact that the next generations of differentiations in the form of ulvØspinel lattice, and the fine spinel lenses of the hercynite-pleonaste series were segregated from the magnetite crystal lettice. This second generation shows the features of the first stage of the processes which have initiated the series of titanium-bearing magnetite, described above