Ti-Al zoning of experimentally grown titanite in the system CaO-Al2O3-TiO2-SiO2-NaCl-H2O-(F): Evidence for small-scale fluid heterogeneity
-
Friedrich Lucassen
,
Dieter Rhede
Abstract
Chemical zoning according to the substitution Al + (OH,F) = Ti + O is a common phenomenon in natural titanite and can be used to reconstruct its growth conditions. We synthesized titanite, which has a zoning pattern similar to that found in natural titanite that grew at the expense of rutile, visible in element distribution maps as a patchy irregular pattern. Run conditions in the system CaO-Al2O3- TiO2-SiO2-NaCl-H2O(-CaF2) were 600 °C, 0.4 GPa, 1 to 107 days duration. Natural rutile crystals were placed in a perforated Pt-tube within an outer Au-capsule containing wollastonite, γ-Al2O3, optionally powdered CaF2, and a NaCl brine, to simulate conditions, where rutile is transformed into titanite by a hydrous Ca-Si-Al(-F) fluid, driven by a chemical potential gradient between inner and outer capsule. Spontaneous nucleation of titanite is restricted to a small number of crystals on the rutile surface in the inner capsule. Growth proceeds from sparse isolated titanite crystals after 1 day to assemblages of several 100 μm large crystals in a reaction rim in the long-time runs. Titanite is strongly zoned in Al-Ti and shows up to ~0.5 Al per formula unit (pfu) in experiments containing F; without F, substitution is limited to ~0.25 Al pfu. The range of the Ti-Al exchange is already large in short run times and the same heterogeneity is observed in long-time runs. The Al-Ti distribution (with and without F) in compositional domains (up to several tens of micrometers) is patchy and irregular. No relation of the zoning with time (core-rim) or preferred growth directions was observed.
In the case of fluid-mediated growth, mineral growth zoning represents a disequilibrium at supersaturated conditions. The concentration of Ti in the fluid is likely the limiting factor for titanite growth considering the low solubility compared to that of Al, Ca, and Si. Titanium is not transported in significant amounts into the outer capsule, indicating low mobility, in contrast to Al, Ca, and Si, which are transported into the inner capsule. Assuming buffered Al concentration from dissolution of the Al-source, we speculate that the Ti/Al of the fluid at the precipitation site was controlled by the local Ti concentration, which varies over the distance from the rutile surface to the growing titanite crystal and produces the irregular patchy zoning.
© 2015 by Walter de Gruyter Berlin/Boston
Articles in the same Issue
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Articles in the same Issue
- Ti-Al zoning of experimentally grown titanite in the system CaO-Al2O3-TiO2-SiO2-NaCl-H2O-(F): Evidence for small-scale fluid heterogeneity
- A new method for quantitative petrography based on image processing of chemical element maps: Part I. Mineral mapping applied to compacted bentonites
- A new method for quantitative petrography based on image processing of chemical element maps: Part II. Semi-quantitative porosity maps superimposed on mineral maps
- Enhancement of solid-state reaction rates by non-hydrostatic stress effects on polycrystalline diffusion kinetics
- (H3O)Fe(SO4)2 formed by dehydrating rhomboclase and its potential existence on Mars
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- Density and seismic velocities of chromitite body in oceanic mantle peridotite
- Packing schemes of cavities in selected clathrasils and zeolites and the analogous packings of atoms in crystal structures
- Temperature dependence of IR absorption of OH species in clinopyroxene
- Thermal behavior of vibrational phonons and hydroxyls of muscovite in dehydroxylation: In situ high-temperature infrared spectroscopic investigations
- Kinetics of Fe-oxidation/deprotonation process in Fe-rich phlogopite under isothermal conditions
- On the crystal chemistry of londonite [(Cs,K,Rb)Al4Be5B11O28]: A single-crystal neutron diffraction study at 300 and 20 K
- High-pressure melting of wüstite
- Primary Nb-Ta minerals in the Szklary pegmatite, Poland: New insights into controls of crystal chemistry and crystallization sequences
- Evolution of the interlayer space of hydrated montmorillonite as a function of temperature
- Morphology of pyrite in particulate matter from shallow submarine hydrothermal vents
- Influence of the fluid composition on diamond dissolution forms in carbonate melts
- Far infrared spectroscopy of carbonate minerals
- Assessment of the diamond-trap method for studying high-pressure fluids and melts and an improved freezing stage design for laser ablation ICP-MS analysis
- Françoisite-(Ce), a new mineral species from La Creusaz uranium deposit (Valais, Switzerland) and from Radium Ridge (Flinders Ranges, South Australia): Description and genesis
- Crystal chemistry and origin of grandidierite, ominelite, boralsilite, and werdingite from the Bory Granulite Massif, Czech Republic
- Lead-tellurium oxysalts from Otto Mountain near Baker, California: III. Thorneite, Pb6(Te26+O10)(CO3)Cl2(H2O), the first mineral with edge-sharing octahedral tellurate dimers
- Lead-tellurium oxysalts from Otto Mountain near Baker, California: IV. Markcooperite, Pb(UO2)Te6+O6, the first natural uranyl tellurate
- Lead-tellurium oxysalts from Otto Mountain near Baker, California: V. Timroseite, Pb2Cu52+(Te6+O6)2(OH)2, and paratimroseite, Pb2Cu42+(Te6+O6)2(H2O)2, two new tellurates with Te-Cu polyhedral sheets
- Lead-tellurium oxysalts from Otto Mountain near Baker, California: VI. Telluroperite, Pb3Te4+O4Cl2, the Te analog of perite and nadorite
- The determination of sulfate and sulfide species in hydrous silicate glasses using Raman spectroscopy
- The structure of crystals, glasses, and melts along the CaO-Al2O3 join: Results from Raman, Al L- and K-edge X-ray absorption, and 27Al NMR spectroscopy
- Ordering of iron vacancies in monoclinic jarosites
