Abstract

Rock massifs traditionally used for the construction of foundations, tunnels or as a source of crushed stone, frequently contain compositionally (texturally, mineralogically, geochemically) contrasting inclusions – xenoliths. The presence of xenoliths is a commonly overlooked fact which may, however, significantly affect the total strength of the massifs. The most frequent xenoliths in igneous massifs are mafic microgranular enclaves occurring as ellipsoidal inclusions with the size varying from centimetre to metre scales in the host rocks. Our pilot experimental study brings a complex assessment of strength properties (e.g., rebound hardness, uniaxial compressive strength, rock tensile strength) of multicomponent geomaterials, i.e., host-rocks and their enclaves, sampled both from quartz-rich (granitoid) and quartz-poor (syenitoid) massifs.

1. Introduction

Rock mechanics is a dynamically developing scientific discipline integrating a range of modern geological and geotechnical approaches [1, 2]. This discipline is absolutely irreplaceable in the study of the behaviour of geomaterials and rock massifs affected by civil engineering works.

Rock massifs frequently contain compositionally (texturally, mineralogically, geochemically) different parts generally described under the term xenoliths (from ancient Greek: "foreign rock") [3]. The presence of xenoliths is a commonly overlooked fact in rock mechanics that, nevertheless, can significantly affect the total strength of the massifs [4].

2. Mafic microgranular enclaves

The most frequent xenoliths in igneous rocks are mafic microgranular enclaves occurring both in quartz-rich (granitoid) and quartz-poor (syenitoid) massifs [4–7]. The shape of mafic microgranular enclaves is mostly ellipsoidal with the size varying from centimetre to metre scales. The name "mafic microgranular enclaves" reflects their high contents of dark (mafic) minerals (dark micas, amphiboles) and fine- to medium-grained, equigranular texture (Fig. 1A).

Genetically, the mafic microgranular enclaves represent relatively rapidly chilled "drops" of more basic (mafic) melt which was variably mingled with the surrounding felsic melt characterized by higher content of SiO2 [8–11]. Thus, mafic microgranular enclaves are usually preferentially oriented (stretched) in the flow direction of the host magma.

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