Abstract
The ultramafic rocks of the Kan block, East Sayan, are confined mainly to the Idar greenstone belt. In terms of formational affiliation, they are subdivided into two groups: magmatic (Kingash Complex) and residual (Idar Complex) ones. The magmatic ultramafic rocks compose hypabyssal and subvolcanic bodies, which are represented by rocks of dunite-wehrlite-picrite association with cumulate textures. Uninterrupted chemical variations of the magmatic ultramafic rocks indicate subsequent magmatic differentiation of parental picritic melt in the intermediate deep-seated chambers and emplacement of its derivatives in the crystallization site. Differentiation leads to proportional increase of all rare-earth and other incompatible elements. The residual ultramafics occur as boudined dunite-harzburgite bodies showing metamorphic granoblastic textures. They have more homogenous chemical composition close to those of ophiolite complexes, which represent strongly depleted mantle rocks brought to the upper lithospheric levels via deep-seated thrusts. Residual ultramafics differ from magmatic rocks in notably lower contents of some trace and rare earth elements.
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