Marble Mélange: Composition Variations and Formation Mechanisms

Abstract

The Olkhon terrane in the Western Baikal area accommodates four types of carbonate-silicate mixtures: injection (protrusion), metamorphic-boudinated, mingling, and tectonite marble mélange. The outcrops of injection mélange consist of a carbonate matrix with inclusions of native silicic rocks found in the immediate vicinities, commonly cover large areas and lack any distinct linearity in the map view. Mélange of the metamorphic boudinage type comprises diopsidite and tremilote-diopsidite fragments in a dolomitic or calcite-dolomitic matrix. Its origin is apparently due to tectonism and related metamorphism of quartz sandstones in Neoproterozoic strata on the passive margin of the Siberian craton. Mingling mélange appears as calcite marble or carbonate-silicate (calciphyre) veins with metadolerite and granite inclusions of different sizes. The veins formed by intrusion of carbonate and silicate melt batches and subsequent fragmentation of silicate rocks that crystallized earlier. Marble tectonites localized in narrow zones record the late phase of ductile marble injection.