Calcite deformation

Wollast R. and Marijns A. (1980) Mecanisme de dissolution des calcites magnesiennes naturelles. Cong. "Cristallisation, Deformation, Dissolution des Carbonates." Bordeaux, Nov. 1980, 477-486. 

Calcite and dolomite form large parts of the sedimentary continental crust. Consequently, their mechanical properties have been studied in some detail, and Wenk et al. (1983) have reviewed the rheology and associated microstructural development. Deformation takes place by both twinning and dislocation glide. 

Microstructures in deformed dolomite. The deformation characteristics of dolomite are markedly different from those of calcite and have been studied in detail by Barber, Heard, and Wenk (1981). Not only are the twin laws different, but twinning in dolomite occurs only at temperatures above about 250°C. The lower dislocation densities observed in twinned dolomite and at twin intersections is perhaps due to the greater ease of stress relaxation at the higher temperatures required for twinning. 

Barber, D. J., Wenk, H.-R. (1979). Deformation twinning in calcite, dolomite, and other rhombohedral carbonates. Phys. Chem. Minerals, 5,141-65. 

The above evidence establishes that fracturing and seismic behavior can extend well into the zone of mid to lower crustal metamorphism at rock pressures of —0.5-1 GPa. Veins preserve a valuable record of this brittle deformation they are fractures in which mineral mass has been deposited. The most common vein-forming minerals are quartz, calcite, and the feldspars, but a huge variety of other minerals are also observed. Fractures tend to focus flow, because they are zones of elevated permeability. Fracture flow is commonly approximated using the well-known expression from fluid mechanics for laminar flow between two parallel plates (e.g., White, 1979). For a set of parallel fractures, the flux is approximated by (e.g., Norton and Knapp, 1977) ... 

Sandstones may, however, become calcite cemented due to aragonite and Mg-calcite dissolution at very shallow depth (even at the surface). When cemented, the sediments may obtain brittle properties and deform by cataclasis and brecciation. Another source for early cement within sandstones is biogenic silica which acts as a precursor for silica cements at relatively shallow depth (ca. 1500 m). Clean quartz sandstones, however, are usually not cemented until the sediment has reached a considerable depth (approx. 3 km). Brittle deformation, which may occur in cemented sandstones, prevents fault planes closing entirely and can augment a fault-parallel permeability which increases the potential for mineralization. 

Cements cc, calcite qz, quartz. Deformation characteristics IFF, interparticulate flow Ph, enrichment of phyllosilicates CS, clay smear ShS, shale smear BR, brecciation CC, cataclasis. 

In other sandstones with a relatively compacted fabric, biotites are deformed, plagioclase is partially dissolved and calcite cements partially replace dissolved plagioclase or, more commonly, enclose kaolinite in intergranular pore space (Fig. 4D). This kaolinite has been demonstrated to be a byproduct of plagioclase dissolution (Boles, 1984). Fracture-fill calcite is minor but tends to be more common in the relatively compacted sands, where grains have been fractured and micas crushed (Fig. 4D). These calcite cement occurrences in altered sandstones are interpreted to be a later generation than those occurring in less altered rock. 

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