Diffusion of phosphorus in olivine and molten basalt
-
E. Bruce Watson
,
D.J. Cherniak
Abstract
The diffusivity of phosphorus in San Carlos olivine (SCO) was measured at near-atmospheric pressure and 650-850 °C by in-diffusion of P from a surface powder source consisting of pre-reacted SCO and AlPO4. The experiments were conducted in evacuated silica-glass ampoules at oxygen fugacities fixed by solid-state buffers, generally Ni-NiO but also including two experiments buffered at wüstite-magnetite. Phosphorus uptake profiles were characterized by Rutherford backscattering spectroscopy (RBS) and nuclear reaction analysis (NRA). The temperature dependence of P diffusion in SCO conforms to the expected Arrhenius relation D = D0exp(-Ea/RT), where the constants are as follows: log(D0, m2/s) = -10.06 ± 0.80 and Ea = 229 ± 16 kJ/mol. These values characterize P as a relatively slow diffuser in olivine-slower by about an order of magnitude than Cr and Ca at basalt near-liquidus temperatures-but substantially faster than Si.
With a view toward modeling P uptake during rapid growth of natural olivines, P diffusion was also characterized in dry MORB basalt melt over the temperature range 1250-1500 °C at 1 GPa, using traditional diffusion couples contained in graphite. Phosphorus diffusion profiles in the quenched and depressurized samples were quantified by laser-ablation ICP/MS. Phosphorus diffusion in basaltic melt is similar to that of Si, with log(D0, m2/s) = -6.30 ± 0.7 and Ea = 147 ± 22 kJ/mol.
The new data for P diffusion in olivine and basalt melt can be used to explore the acquisition of finescale zoning in natural olivine phenocrysts through kinetic models, as well as the survival of P zoning in olivine with time spent at elevated temperature. Models of growth entrapment of a P-enriched near-surface layer in the olivine lattice indicate that crystal growth at plausible sustained rates is indeed likely to result in regions of anomalously high P content in the resulting crystal. Phosphorus concentrations above the equilibrium partitioning value can also result from development of a diffusive boundary layer in the melt against a rapidly growing crystal, but this mechanism is ineffective at typical sustained olivine growth rates, requiring dendrite-forming growth speeds. Preservation of P zoning on the scale of a few micrometers apparently requires cooling within a few months of formation of the zoning.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Reaching new boundaries for in-situ U-Th geochronology
- Normal to inverse transition in martian spinel: Understanding the interplay between chromium, vanadium, and iron valence state partitioning through a crystal-chemical lens
- Accuracy of timescales retrieved from diffusion modeling in olivine: A 3D perspective
- Phosphoran olivine overgrowths: Implications for multiple impacts to the Main Group pallasite parent body
- Diffusion of phosphorus in olivine and molten basalt
- Oceanic lavas sampling the high-3He/4He mantle reservoir: Primitive, depleted, or re-enriched?
- U-Th baddeleyite geochronology and its significance to date the emplacement of silica undersaturated magmas
- Polycrystallinity of green rust minerals and their synthetic analogs: Implications for particle formation and reactivity in complex systems
- Fe pre-enrichment: A new method to counteract iron loss in experiments on basaltic melts
- Fe-Mg diffusion in spinel: New experimental data and a point defect model
- Age, petrochemistry, and origin of a REE-rich mineralization in the Longs Peak-St. Vrain batholith, near Jamestown, Colorado (U.S.A.)
- Laser-induced breakdown spectroscopy (LIBS) as a tool for in situ mapping and textural interpretation of lithium in pegmatite minerals
- Evidence for Nb2+ and Ta3+ in silicate melts under highly reducing conditions: A XANES study
- Elastic softening of leucite and the lack of polar domain boundaries
- New thermobarometers for martian igneous rocks, and some implications for secular cooling on Mars
- An updated calibration of the plagioclase-liquid hygrometer-thermometer applicable to basalts through rhyolites
- Water effects on the anharmonic properties of forsterite
- Synthesis and structure of a stuffed derivative of α-quartz, Mg0.5AlSiO4
- Equation of state and elasticity of the 3.65 Å phase: Implications for the X-discontinuity
- Ca-Zn solid solutions in C2/c pyroxenes: Synthesis, crystal structure, and implications for Zn geochemistry
- Aluminum environments in synthetic Ca-Tschermak clinopyroxene (CaAlAlSiO6) from Rietveld refinement, 27Al NMR, and first-principles calculations
- Trioctahedral Fe-rich micas: Relationships between magnetic behavior and crystal chemistry
- High-pressure compressibility and phase stability of Mn-dolomite (kutnohorite)
- Composition dependence of spin transition in (Mg,Fe)SiO3 bridgmanite
- Oriented multiphase needles in garnet from ultrahigh-temperature granulites, Connecticut, U.S.A.
- Solubility and solution mechanisms of chlorine and fluorine in aluminosilicate melts at high pressure and high temperature
- Volatiles in magmas related to the Campanian Ignimbrite eruption: Experiments vs. natural findings
- Aluminosilicate melts and glasses at 1 to 3 GPa: Temperature and pressure effects on recovered structural and density changes
- Role of volatiles (S, Cl, H2O) and silica activity on the crystallization of haüyne and nosean in phonolitic magmas (Eifel, Germany and Saghro, Morocco)
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- Synthesis of large wadsleyite single crystals by solid-state recrystallization
- Decagonite, Al71Ni24Fe5, a quasicrystal with decagonal symmetry from the Khatyrka CV3 carbonaceous chondrite
- Earth’s “missing” minerals
- Magnetite-rutile symplectite derived from ilmenite-hematite solid solution in the Xinjie Fe-Ti oxide-bearing, mafic-ultramafic layered intrusion (SW China)
- New Mineral Names
- Book Review: Arsenic: Environmental Geochemistry, Mineralogy, and Microbiology, RIMG Volume 79.
