On the significance of argon release from biotite and amphibole during sup 40 Ar/ sup 39 Ar vacuum heating

Journal Article · Sat Oct 01 04:00:00 EDT 1988 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(88)90304-3· OSTI ID:5207234

Gaber, L J; Foland, K A; Corbato, C E ^[1]

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1. Ohio State Univ., Columbus (USA)

The nature of Ar release from biotite and amphibole is addressed via vacuum-heating experiments followed by measurements of {sup 40}Ar loss and unit cell parameters and scanning electron microscope observations of the heated specimens. {sup 40}Ar diffusion during hydrothermal heating was previously reported for the studied biotite and amphibole specimens allowing direct comparison to the Ar loss kinetics from vacuum heating. The results demonstrate conclusively that volume diffusion is not the mechanism controlling Ar loss during normal {sup 40}Ar/{sup 39}Ar measurements. These hydrous minerals also suffer weight loss and irreversible structural changes in the range 600 to 800{degree}C. Moreover, biotite suffers morphological modifications dramatically expressed by splitting along the basal cleavage. A few experiments on muscovite suggest similar weight loss and splitting effects. The behavior of these minerals has important implications for the interpretation of {sup 40}Ar/{sup 39}Ar step-heating data. The Ar-loss kinetics of {sup 40}Ar/{sup 39}Ar experiments cannot be used to calculate diffusion coefficients and it is inappropriate to estimate closure temperatures from such data. The morphological changes will not permit the meaningful resolution of fossil Ar gradients which may have been present in the initial grains.

• OSTI ID: 5207234
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Journal Name: Geochimica et Cosmochimica Acta; (USA) Vol. 52:10; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400800* -- Combustion
Pyrolysis
& High-Temperature Chemistry
58 GEOSCIENCES
580000 -- Geosciences
AMPHIBOLE
ARGON
ARGON 39
ARGON 40
ARGON ISOTOPES
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BIOTITE
CHEMICAL COMPOSITION
CHEMISTRY
DISSOCIATING GASES
DISSOCIATION
ELECTRON MICROSCOPY
ELEMENTS
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
FLUIDS
GASES
GEOCHEMISTRY
ISOTOPES
KINETICS
LIGHT NUCLEI
MICA
MICROSCOPY
MINERALS
NONMETALS
NUCLEI
PHYSICAL PROPERTIES
RADIOISOTOPES
RARE GASES
REACTION KINETICS
SCANNING ELECTRON MICROSCOPY
SILICATE MINERALS
STABLE ISOTOPES
TEMPERATURE EFFECTS
THERMODYNAMIC PROPERTIES
YEARS LIVING RADIOISOTOPES