Oscillatory zoning of Mn in solution-grown calcite crystals

doi:10.1016/0012-8252(0)90026-R

Earth-Science Reviews

Volume 29, Issues 1–4, October 1990, Pages 39-46

https://doi.org/10.1016/0012-8252(0)90026-R Get rights and content

Abstract

Oscillatory zoning of Mn in calcite was produced in free-drift solution growth experiments. The repetitive Mn-doped subzones, imaged using cathodoluminescence microscopy, are not correlated with external controls or perturbations, and they generally cannot be correlated between crystals. The fluctuations causing the oscillatory zoning form autonomously in a system far from equilibrium and represent an example of self-organization.

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Nanoinclusions in zoned magnetite from the Sossego IOCG deposit, Carajás, Brazil: Implication for mineral zoning and magnetite origin discrimination
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Citation Excerpt :
However, this model cannot be used to explain the formation of oscillatory zoning in the studied magnetite, because of absence of typical features of dissolution and reprecipitation such as pervasive porosity and sharp reaction front at both the micron and nanometer scale (Putnis and Austrheim, 2013). Calcite growth experiments have demonstrated that the oscillatory zoning in calcite is not consistent with external perturbations such as variation in fluid compositions (Reeder et al., 1990). The relatively stable temperature and oxygen fugacity conditions at Sossego precludes major control of external factors on the formation of oscillatory zoning in magnetite.
Compositional zoning is common in magnetite from different geological environments, but its formation mechanism remains controversial. Here, we characterize micron- to nano-scale textural and chemical variations in zoned magnetite from the Sossego iron oxide-copper–gold deposit (Carajás, Brazil) using electron probe microanalyzer (EPMA) and transmission electron microscopy (TEM). Lack of porosity and of a reaction front at both the micron and nanometer scales indicates that compositional zoning in magnetite is a pristine texture formed during crystal growth, rather than a secondary texture due to dissolution and reprecipitation reaction. TEM energy dispersive X-ray spectrometry analyses and mapping identify four types of nanoinclusions in zoned magnetite: 1) Mg-Fe-Al silicates, most likely amphibole, 2) Fe-Ti oxides, mainly ilmenite, 3) pyroxene, 4) Si-rich magnetite. The formation of ilmenite nanoinclusions in Sossego magnetite is possibly due to oxy-exsolution of ulvöspinel from Ti-rich magnetite, whereas nanoinclusions of other minerals likely formed by local supersaturation in the fluid boundary layer, followed by magnetite crystal entrapment. Compositional zoning in magnetite likely formed by a self-organization process where fluid composition fluctuations are feedback responses for an evolving fluid system far from equilibrium, rather than cyclic variations in external factors such as temperature and oxygen fugacity. Saturation of silicate minerals results in relative depletion of Si, Ca, and Al in boundary layer fluids, and formation of inclusion-poor zone depleted in these elements. Nanoinclusions in magnetite highlight the importance of textural characterization when using in situ chemical composition to discriminate the origin of magnetite. In addition, the assemblages of nanoinclusions in magnetite can be used to complement the discrimination of magnetite origins.
Dolomitization micro-conditions constraint on dolomite stoichiometry: A case study from the Miocene Huangliu Formation, Xisha Islands, South China Sea
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As suggested by Jones and Luth (2002), alternating HCD and LCD zones in the dolomite crystals of the Cayman Formation are akin to oscillatory zoning (cf., Shore and Fowler, 1996). Such zoning, also evident in dolomite crystals in the Huangliu Formation, is a common phenomenon in many minerals (Shore and Fowler, 1996) that may be controlled by intrinsic factors such as growth inhibitor adsorption and/or extrinsic factors such as fluid composition, temperature, salinity, or alkalinity (e.g., Shore and Fowler, 1996; Reeder et al., 1990). Dolomitization is generally considered to be a dissolution – reprecipitation phenomenon that involves dissolution, transportation of ions, and precipitation (e.g., Katz and Matthews, 1977; Veizer, 1983; Putnis and John, 2010; Mueller et al., 2010; Jonas et al., 2015).
The micro-conditions that control dolomitization processes were still not well known in natural environments. Cenozoic “island dolostones” are ideal for examining the processes since they are geologically young and have not experienced deep burial conditions. Miocene dolostones from the Xisha Islands, located in the South China Sea, are similar to those found on Grand Cayman Island, located in the Caribbean Sea. These dolostones are composed of low-Ca dolomite (LCD, < 55 mol % CaCO₃; hereafter referred to as %Ca) and high-Ca dolomite (HCD, > 55 %Ca). Individual dolomite crystals are commonly formed entirely of LCD or HCD, and/or HCD cores that are encased by LCD and alternating zones of HCD and LCD (1–10 μm thick). The crystal textures indicate that the LCD and HCD are primary growth features (no obvious recrystallization) that formed as the dolomite replaced the limestone precursor. The compositional features (%Ca in LCD and HCD, average %Ca, and proportion of LCD and HCD) and geochemical parameters (O/C isotopes, Sr, Fe and Mn) of dolomite indicate that the Mg was incorporated into dolomite crystals in an orderly manner that was mainly controlled by the interaction of fluid properties and crystal structure. The fact that dolomite stoichiometry varied laterally and vertically throughout the successions shows that micro-scale physicochemical conditions played a critical role in the evolution of individual dolomite crystals. The similarities between the dolostones of the Xisha Islands and Grand Cayman, which are 15,795 km apart, indicate that the factors that control the micro- and large-scale features of these dolostones must have undergone similar processes or experienced similar physicochemical conditions despite their disparate settings.
In-situ calcite U-Pb geochronology of hydrothermal veins in Thailand: New constraints on Indosinian and Cenozoic deformation
2021, Journal of Asian Earth Sciences
Citation Excerpt :
Ablation targets that were set close to boundaries between high and low Mn zones produced mixing ages between both populations (Figs. 7, 9). Chemical zonation within calcite may represent changes in fluid chemistry (and thus potentially different fluid-flow events), or changes in uptake of metals (e.g. Barker and Cox, 2011; Paquette and Reeder, 1995; Reeder et al., 1990). Experimental evidence (Frank et al., 1982) demonstrates that Mn can show oscillatory zoning during calcite growth, related to uptake of Mn2+ along the calcite crystal surface that inhibits crystal growth.
U-Pb dating of calcite veins allows direct dating of brittle deformation events. Here, we apply this method to hydrothermal calcite veins in a fold-and-thrust belt and a large scale strike-slip fault zone in central and western Thailand, in an attempt to shed new light on the regional upper crustal deformation history. Calcite U-Pb dates for the Khao Khwang Fold and Thrust Belt (KKFTB) of 221 ± 7 Ma and 216 ± 3 Ma demonstrate that calcite precipitated during tectonic activity associated with stage II of the Indosinian Orogeny (Late Triassic – Early Jurassic). One additional sample from the KKFTB suggests that the Indosinian calcite has locally been overprinted by a Cenozoic fluid event with a different chemistry. For the Three Pagodas Fault Zone (TPFZ), our calcite U-Pb results suggest a complex, protracted history of Cenozoic brittle deformation. Petrographic information combined with contrasting redox-sensitive trace elemental signatures suggest that the vein arrays in the TPFZ precipitated during two distinct events of brittle deformation at ~48 and ~23 Ma. These dates are interpreted in the context of far-field brittle deformation related to the India-Eurasia collision. The presented calcite U-Pb dates are in excellent agreement with published age constraints on the deformation history of Thailand, demonstrating the utility of the method to decipher complex brittle deformation histories. The paper further illustrates some of the complexities in relation to calcite U-Pb dating and provides suggestions for untangling complex datasets that could be applied to future studies on the deformation history of Thailand and other regions.
Geochemical controls on the elemental composition of siderite: Implications for palaeo-environmental reconstructions
2020, Geochimica et Cosmochimica Acta
Citation Excerpt :
Because trace elements are likely to be incorporated at rates that differ from the rate of Fe2+ incorporation into siderite, this may lead to the development of a solution boundary layer that is either depleted in the trace element (i.e., if Kd > 1) or enriched in the trace element (i.e., if Kd < 1). This will, in turn, influence the effective Kd, rate of cation diffusion to the growing surface, and/or influence the overall growth rate of the mineral (i.e., lead to oscillatory zoning; Reeder et al., 1990; Wang and Merino, 1992). This relationship predicts that trace elements where the apparent distribution coefficient is > 1 should exhibit an increase in element uptake with decreasing growth rate.
The elemental composition of siderite (FeCO₃) has been widely used as a palaeo-environmental proxy, and commonly utilised in the diagnosis of marine influences on Phanerozoic coastal wetland sediments. That siderite might reflect marine or freshwater sources is based on the premise that a marine origin should show an enrichment of Ca and/or Mg, while high concentrations of Mn should reflect precipitation from freshwater. However, the main controls on the elemental composition of siderite, and the degree to which siderite composition reflects parent water chemistry, are poorly understood. To address these issues, we conducted siderite nucleation and seeded growth experiments to examine element partitioning at a variety of saturation states and solution compositions (i.e., cation concentrations, pH, and pCO₂). Results indicate a strong preference for Mn uptake over Ca and Mg, even when Mn is present at concentrations far below those of Ca or Mg. This uptake is enhanced at slower growth rates and lower saturation states, which may, in part, reflect surface structural controls on uptake and or a change in the dominant growth mechanism. Ca uptake only occurred during nucleation experiments, while measurable Mg uptake was not observed in experiments conducted at 20 °C, but increased slightly at 55 °C. These results suggest that the chemical composition of siderite does not directly reflect aqueous cation chemistry as previously assumed and is strongly influenced by kinetics rather than equilibrium behaviour. This leads us to conclude that variations in pore water chemistry alone cannot explain the range of Ca and Mg concentrations reported from geological siderites, and that other factors must be considered (such as physical admixtures of multiple carbonate minerals and/or the products of diagenetic recrystallization).

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Oscillatory zoning of Mn in solution-grown calcite crystals

Abstract

Mar. Chem.

J. Cryst. Growth

Geochim. Cosmochim. Acta

J. Cryst. Growth

Earth-Sci. Rev.

Geochim. Cosmochim. Acta

Oscillatory zoning: a pathological case of crystal growth

Nature

Some observations on oscillatory zoning and crystallization of magmatic plagioclase

Am. Mineral.

Iron and manganese incorporation into calcite cements: implications for diagenetic studies

Abstr. Progr., Geol. Soc. Am. Annu. Mtg.