Hydrogen Incorporation in Plagioclase
Jed L Mosenfelder1, Janine L Andrys1, Anette VON DER Handt1
1Department of Earth and Environmental Sciences, University of Minnesota, 150 Tate Hall, Minneapolis, MN, 55455, U.S.A.
Geochimica Et Cosmochimica Acta
|July 2, 2020
Summary
Hydrogen solubility in plagioclase (Pl) increases significantly at low oxygen fugacity (fO2), particularly at higher temperatures. This enhanced H incorporation is linked to iron reduction and defect formation, impacting models of planetary water content.
Area of Science:
- Geochemistry
- Mineral Physics
- Planetary Science
Background:
- Understanding hydrogen (H) solubility in mantle minerals like plagioclase (Pl) is crucial for interpreting planetary water content.
- Previous studies have indicated a dependence of H solubility on experimental conditions, but mechanisms remain debated.
Purpose of the Study:
- To experimentally determine hydrogen solubility in plagioclase across a range of compositions (An15 to An94) under varying pressure, temperature, and oxygen fugacity (fO2) conditions.
- To elucidate the primary mechanisms of hydrogen incorporation into the plagioclase structure.
- To assess the implications of these findings for lunar and terrestrial magmatic processes.
Main Methods:
- High-pressure and high-temperature experiments (700-850 °C, 0.5 GPa) using Ni-NiO (NNO) and iron-wüstite (IW) oxygen buffers.
- Analysis of hydrogen solubility in plagioclase samples with varying anorthite content (An15-An94).
- Inference of H incorporation mechanisms by analogy with synthetic hydrogen feldspar and analysis of plagioclase structure.
Main Results:
- Hydrogen solubility in plagioclase is enhanced by a factor of ~2-3 at low fO2 (IW) compared to high fO2 (NNO) at 800-850 °C, especially in more iron-rich compositions.
- At 700 °C, H solubility shows no fO2 dependence for An15 plagioclase.
- The predominant H incorporation mechanism involves bonding to oxygen atoms adjacent to M-site vacancies, facilitated by Fe3+ reduction to Fe2+ at low fO2.
Conclusions:
- Low oxygen fugacity significantly enhances structural hydrogen incorporation in plagioclase by promoting defect formation.
- This mechanism is critical for understanding water content in the lunar magma ocean and explaining terrestrial plagioclase xenocrysts.
- Further research is needed to explore H substitution on tetrahedral vacancies and coupled H-F substitution.
Related Concept Videos
01:04Hydrogen Bonds
12.6K
A hydrogen bond is formed when a weakly positive hydrogen atom already bonded to one electronegative atom (for example, the oxygen in the water molecule) is attracted to another electronegative atom from another polar molecule, such as water (H2O), hydrogen fluoride (HF), or ammonia (NH3). The huge electronegativity difference between the H atom (2.1) and the atom to which it is bonded (4.0 for an F atom, 3.5 for an O atom, or 3.0 for an N atom), combined with the very small size of an H atom...
12.6K
00:26Hydrogen Bonds
129.3K
Hydrogen bonds are weak attractions between atoms that have formed other chemical bonds. One of these atoms is electronegative, like oxygen, and has a partial negative charge. The other is a hydrogen atom that has bonded with another electronegative atom and has a partial positive charge.
Hydrogen Bonds Control the World!
Because hydrogen has very weak electronegativity when it binds with a strongly electronegative atom, such as oxygen or nitrogen, electrons in the bond are unequally shared....
Hydrogen Bonds Control the World!
Because hydrogen has very weak electronegativity when it binds with a strongly electronegative atom, such as oxygen or nitrogen, electrons in the bond are unequally shared....
129.3K
02:35Electrophilic Addition to Alkynes: Hydrohalogenation
11.1K
Electrophilic addition of hydrogen halides, HX (X = Cl, Br or I) to alkenes forms alkyl halides as per Markovnikov's rule, where the hydrogen gets added to the less substituted carbon of the double bond. Hydrohalogenation of alkynes takes place in a similar manner, with the first addition of HX forming a vinyl halide and the second giving a geminal dihalide.
11.1K
03:35Hybridization of Atomic Orbitals II
46.8K
sp3d and sp3d 2 Hybridization
46.8K
01:26Radical Substitution: Hydrogenolysis of Alkyl Halides with Tributyltin Hydride
2.2K
Radical substitution reactions can be used to remove functional groups from molecules. The hydrogenolysis of alkyl halides is one such reaction, where the weak Sn–H bond in tributyltin hydride reacts with alkyl halides to form alkanes. Here, the reagent Bu3SnH yields tributyltin halide as a byproduct.
The bonds formed in this reaction are stronger than the bonds broken, making it energetically favorable. The reaction follows a radical chain mechanism similar to radical halogenation reactions,...
The bonds formed in this reaction are stronger than the bonds broken, making it energetically favorable. The reaction follows a radical chain mechanism similar to radical halogenation reactions,...
2.2K
01:01Acid Halides to Carboxylic Acids: Hydrolysis
3.4K
Hydrolysis of acid halides is a nucleophilic acyl substitution reaction in which acid halides react with water to give carboxylic acids. The reaction occurs readily and does not require acid or a base catalyst.
As shown below, the mechanism involves a nucleophilic attack by water at the carbonyl carbon to form a tetrahedral intermediate. This is followed by the reformation of the carbon–oxygen π bond along with the departure of a halide ion. A final proton transfer step yields carboxylic...
As shown below, the mechanism involves a nucleophilic attack by water at the carbonyl carbon to form a tetrahedral intermediate. This is followed by the reformation of the carbon–oxygen π bond along with the departure of a halide ion. A final proton transfer step yields carboxylic...
3.4K