MAFIC DIKE BELTS IN ZHARMA ZONE OF EASTERN KAZAKHSTAN: POSITION, AGE AND GEODYNAMIC IMPLICATION

Abstract

The results of studying the geological position, composition and age of the belts of basic dikes within the Zharma zone of East Kazakhstan are presented. Traditionally these belts were considered as manifestations of mantle activity in the intracontinental (postorogenic) setting, and their age was taken as the Early-Middle Triassic. The analysis of the relationship between dike belts and intrusive granitoid complexes shows that dike belts occupy different positions and were formed in several stages. The rocks of the dike belts are represented by dolerites, lamprophyres, diorites, granoidiorites, and granites. The diversity of the composition of basic and intermediate rocks is the result of the evolution of subalkaline basaltic magmas during the fractionation of clinopyroxene. Felsic dyke rocks are formed as a result of melting of crustal substrates under the thermal effect of basaltic magmas The parental basaltic magmas were formed by partial melting of the material of the upper mantle (spinel and garnet peridotites) at degrees of melting from 3 to 12%. Geochronological studies allowed to determine two stages of the formation of dike belts - Middle Carboniferous (315 ± 4 Ma) and Early Permian (292-287 Ma). The presence of Triassic dikes in the Zharma zone has not yet been confirmed. The stages of dike magmatism are in good agreement with the data on the main stages of endogenous activity in the Altai accretion-collision system, recently established on the basis of studies of volcanism, intrusive basic and granitoid magmatism.