DIFFERENTIATION OF SHALLOW INTRUSIVES IN THE MAGMA CHAMBER

Abstract

Estimates of the change in composition of magmas being intruded (proceeding from the composition of the resulting rocks) consider the change in chemical and mineral compositions of successive phases of emplacement (first, second and vein), on the assumption that differentiation processes occur only in the deeper parts of a cooling volume of magma (the intrusive) or in the magma chamber at depth. A change in composition of the rocks and minerals from phase to phase is clearly manifested, as a rule, and of homodromic character. This approach has revealed many trends of differentiation of silicic melts in multiphase intrusives. Detailed study of even small intrusives which crystallized quite rapidly shows that the differentiation is also quite intensive under these conditions. An example is the Zhaksyairtau pluton, located in the western part of the latitudinal branch of the Devonian marginal volcanic belt of Central Kazakhstan. Results of this study are presented.