PECULIARITIES OF THE TRACE ELEMENTS DISTRIBUTION WITHIN CALCIUM AMPHIBOLES OF PRECAMBRIAN METAMORPHIC ROCKS

摘要

Geochemical study of calcium amphiboles from the Precambrian metamorphic complexes of Baltic shield and Eastern Siberia has shown that as the content so the distribution of trace elements in their composition is a function of the metamorphism P-T values, as well as the primary rock composition. With an increase of the metamorphism degree the contents of Ti, Cr, Zr and Y become higher, but the content of Cu decreases. The trace elements distribution is influenced also by the mineral paragenesis and its transformations while the metamorphic process. The regularities of the trace elements behaviour in metamorphic minerals (i.e. in amphiboles also) use to be broken most of all by the polycyclic evolution of the majority of Precambrian complexes due to which minerals of the earlier cycle could not get an equilibrium with conditions of the new metamorphism cycle. Nevertheless, the distribution of some elements in amphiboles, especially in the high temperature facies, gives grounds to expect the bringing out of equlibrium between them (Cr-Ni, V-Fe, Zr-Y). Metasomatic amphiboles formed at the regressive stage of metamorphism differ from the progressing stage amphiboles by the wide variations of some elements which behave themselves as in an open system. In some cases the higher contents were remarked for those trace elements which accompany in metasomatic process an income of the major components. Coefficients of distribution (K_d) between amphibole and rock are varying significantly by their value and changeability within metamorphic and magmatic rocks.