Chemical interdiffusion between Na-series tephritic and phonolitic melts with different H2O content, temperature, and oxygen fugacity values
Creators: name: González-García, Diego
name: Pohl, Florian
name: Marxer, Felix
name: Krasheninnikov, Stepan
name: Almeev, Renat
name: Holtz, François
Publisher: name: Stuttgart : Schweizerbart
Year: 2024
Subjects: subject: Canary Islands
subject: Spain
subject: Alkalinity
subject: Aluminum compounds
subject: Biogeochemistry
subject: Calcium alloys
subject: Carbon
subject: Explosives detection
subject: Gas chromatography
subject: Granite
subject: Inert gases
subject: Interdiffusion (solids)
subject: Magnesium alloys
subject: Nitrogen
subject: Nitrogen oxides
subject: Oxygen
subject: Phosphates
subject: Phosphorus
subject: Radioactivation analysis
subject: Silica
subject: Sodium alloys
subject: Sulfur
subject: Titanium dioxide
subject: Binary diffusion coefficients
subject: Canary islands
subject: Chemical interdiffusion
subject: Condition
subject: Diffusion couple
subject: Ignimbrites
subject: Magma mixing
subject: Magmatisms
subject: Major elements
subject: Oxygen fugacity
subject: diffusion
subject: magmatism
subject: oxygen
subject: phonolite
subject: pressure effect
subject: sodium
subject: temperature gradient
subject: Activation energy
subject: Dewey Decimal Classification::500 | Naturwissenschaften::540 | Chemie
subject: Dewey Decimal Classification::500 | Naturwissenschaften::550 | Geowissenschaften

description: The diffusive exchange of major elements in Na-series tephrite–phonolite diffusion couples with compositions relevant to the Canary Islands magmatism was determined at 300 MPa and variable H2O concentrations (0.3 wt % to 3.3 wt %), temperatures (1150 to 1300 °C), and fO2 levels (NNO−1.5 to NNO+1.7). Composition-dependent effective binary diffusion coefficients were determined from concentration–distance profiles. Results show a wide range of diffusivities for different cations, consistently following the sequence Na Al K ≥ Mg = Fe = Ca &gt; Si &gt; Ti, with a mild diffusivity contrast (0.2–0.8 log units) between tephritic and phonolitic melts. Na is the fastest component, with diffusivities falling ∼ 1.0 log units above those of Si for any given condition. An anomalously fast Al diffusion is observed, with DAl falling ∼ 0.4 log units above Si and ∼ 0.6 log units below Na, suggesting a prevalence of Al–alkali coupling across our range of run conditions. The relationships between log D and H2O content in melt for all cations in an intermediate composition are strongly nonlinear and can be fitted using an exponential function with a convergence in diffusion coefficients for different temperatures with increasing H2O content. Thus, Arrhenius analyses result in a decrease in activation energies from 222–293 kJ mol−1 at 1.7 wt % H2O to 48–112 kJ mol−1 at 3.0 wt % H2O. These results provide new data on chemical interdiffusion in highly alkaline Na-rich melts and suggest that H2O content plays a key role in increasing the chemical efficiency of magma mixing at low temperatures. The obtained dataset is used to test chemical controls of magma mixing in the El Abrigo ignimbrite, Tenerife, where banded pumices involving basanitic–tephritic to phonolitic magmas are common in several compositionally bimodal ignimbrite units.