Geochemical features and age data (obtained by Rb–Sr, K–Ar, Pb–Pb methods) with geological interpretation are given for ultrabasic-basic and granitoid rocks from the central part of the Darasun ore region. The age data obtained are 31S±2 Ma for granitoids and 360±127 Ma for malic rocks. The malic rocks are characterized by high contents of K, Ti, Rb, Ba, Sr and comparatively low concentrations of Ca and IGE. U1trabasic members of the association reveal high magnesium content while basic rocks contain low concentrations of Mg. The granitoid characteristic features allow the rocks to be attributed to the granites of andesite series and the subdivision of the Olekma intrusive complex into two independent complexes to be called in question. The data obtained are in agreement with the geodynamic concept of region development, according to which there was an oceanic gulf of rift origin formed under Californian-type conditions along the Okhotsk-Mongolian zone 410-350 Ma ago, and about 320 Ma ago these conditions were changed into regional compression, with intracontinentai Benioff zones being formed along the Okhotsk-Mongolian lineament, where large volumes of calc-alkaline magmas were generated.
Kazimirovskii et al. (Wed,) studied this question.
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