Formation of primary fluid inclusions under influence of the hydrodynamic environment

Abstract

When crystals grow under convection conditions, the hydrodynamic environment can promote the formation of inclusions in the rear side of the crystals, downstream in relation to the fluid flow. An experimental study of this mechanism of fluid trapping is presented, and the conditions under which hydrodynamics influences growth behaviour are discussed. Crystal growth experiments have been carried out with aqueous solutions in a convection system under controlled conditions of temperature, solution velocity Vs and supersaturation (J� • Growth rates of {Oll) faces of ADP crystals have been measured for different orientations, in relation to the solution flow and for different values of (J� and Vs• It is concluded that hydrodynamics can produce an anisotropy in the contribution of material to crystallographically equivalent faces. At low solution velocities and moderate supersat uration, the growth rate depends on the flow "impact" angle. In contrast, at high solution velocities (Vs> 3 cm.s-l for (J� = 2.45 %) the hydrodynamic configuration has no influence on the growth kinetics.Hydrodynamics can also play an important role in the formation of fluid inclusions during crystal growth. However, this effect only occurs at low solution velocities, when the growth kinetics is controlled by the hydrody namic configuration. Crystals grown at low solution velocities (Vs < 3 cm.s· l for (J� = 2.45 %) show large fluid inclusions in the rear zone. At high solution velocities the mass-transfer is high enough to avoid the hydrodynamic control of growth, and no inclusions are generated by this mechanism.

Experimental study of polycrystal growth from an advecting supersaturated fluid in a model fracture

“…The only difference between these two facets is their orientation with respect to the flow direction. In contrast to the results of Prieto et al. (1996), the growth rates of facets 9 and 10 show no significant dependence on orientation.…”

“…A third aspect that could indicate the palaeoflow direction is the location of fluid inclusions (Prieto et al. 1996).…”

“…Facets, which are located in the shade position with respect to the flow direction, have the lowest growth rates. These aspects were observed in KDP (KH 2 PO 4 ) crystals under laminar flow conditions, where growth rates of well‐oriented facets can be twice as high as growth rates of unfavourable oriented facets (Prieto et al. 1996).…”

Estimating the local paleo-fluid flow velocity: New textural method and application to metasomatism

“…Theirs experiments show that the variation of the bulk growth rate increase at low velocity and high supersaturation. Prieto et al (1996) Control of crystal growth rate could be largely described by the combination of two processes: i) chemical volume diffusion within the boundary layer occurring along the crystal faces; and ii) surface processes (Gilmer et al, 1971 such gradient is dependant on the distance between the considered growthing crystal and his nearest neighbors, because, during growth, a "chemical affinity gradient will arise and persist" forming "depleted zones" that enlarge and coalesce (Carlson 1989, Carlson 1991, Skelton 1997. Carlson (1989) established at each instant a relation of proportionality between the depleted zone and the crystal radius:…”

Crystallization in flow - II. Modelling crystal growth kinetics controlled by boundary layer thickness

“…Gilmer et al developed a unified formulation describing crystal growth rates by considering two kinds of processes: diffusion of solute through a volume of liquid (nearly) at rest relatively to the crystal surface, and reactions at the surface leading to the incorporation of molecules in the lattice. More recently, Prieto et al (1996) considered three orientations: normal facing to the flow, parallel to the flow and in downstream position or ‘ in the shade ’. In the two previous cases, the authors invoked the classical hydrodynamic boundary layer theory to account for mass transfer through the ‘ concentration boundary layer ’, although in Prieto et al (1996, p. 991) are questionable.…”