How travertine veins grow from top to bottom and lift the rocks above them: The effect of crystallization force

Abstract

Travertine mounds form at the mouth of springs where CO 2 degassing drives carbonate precipitation from water fl owing from depth. Building of such mounds commonly involves the successive "stratigraphic" deposition of carbonate layers that precipitate from waters rising from depth along vertical to horizontal open fi ssures that are episodically sealed by radiating crystals. Much more intriguing structures can also be observed, such as widespread horizontal white veins of carbonate with vertical aragonite fi bers, parallel or oblique to the "stratigraphic" travertines, which extend laterally over distances of several tens of meters and could represent up to 50% of the total volume of the travertine mound. Using highly precise U-Th dating, the growth direction of these horizontal veins is shown to be from top to bottom, and this fact clearly indicates that they developed within the mound over a period of ~1000 yr for the vein analyzed. A vein growth mechanism is proposed that is able to uplift the rock above the vein thanks to the force of crystallization. The possible development of such structures in other places and the consequences of reverse growth direction when interpreting travertine data are discussed.

The Force of Crystallization and Fracture Propagation during In-Situ Carbonation of Peridotite

“…Such fluctuations in pressure and/or load on the sample may have also promoted the development of a force of crystallization in experiment R0803. Gratier etal [76] theorized that CO 2 -pressure variations may have been a key factor in the development of a force of crystallization by carbonate precipitation during travertine vein formation, and a similar mechanism may have operated in our experiment. On the other hand, significant CO 2 -pressure fluctuations necessitating pressure corrections also occurred during several other experiments, and it is therefore unlikely that pressure fluctuations alone would have driven the development of a force of crystallization in R0803.…”

Reaction-driven casing expansion: potential for wellbore leakage mitigation

“…Examples of mineral reactions that have been shown or are believed to produce a FoC include (a) uptake of crystallisation water by thenardite to produce mirabilite [35,118], (b) delayed ettringite formation in concrete [37,54,116], (c) serpentinisation and possibly carbonation of peridotite [60,67,68,97,104], (d) replacement of leucite by analcime in low-silica rocks [61], (e) conversion of anhydrite into gypsum [70] and (f) the hydration of metal oxides such as quicklime (CaO) and periclase (MgO) [43,94]. In a geological context, development of a force of crystallisation is widely considered to play an important role in pseudomorphic replacement [40,89], as well as vein formation [40,47,87,114] and reaction-driven fracturing [61,97,100,104]. Despite this previous work on FoC-related processes, relatively few studies have been conducted where the magnitude of the FoC is determined directly.…”

Growth of Calcite in Confinement

“…In Portland cement, CO 2 is slowly adsorbed, and calcite is crystallized in confinement [5]. Confined recrystallization of calcite in other environments has also been shown to create forces that break other mineral grains [6] and lift rock overburden [7].…”

“…The above examples show that carbonate rocks, where the pore fluid becomes supersaturated in calcium carbonate, behave in two completely different manners: sometimes, the calcite crystallizes in the pore space and around grain contacts and cements and strengthens the rock [3], and sometimes, calcite crystallizes in the grain contacts and breaks the surrounding rock [6,7]. Except for a general equilibrium thermodynamic argument for the limit to the force of crystallization [8][9][10], there exists no experimental data or theoretical models to understand the transition from crystallization force to cementation [11].…”