Comparison of sup 40 Ar- sup 39 Ar conventional and laser dating of biotites from the North Tregor Batholith

Journal Article · Sat Jun 01 04:00:00 EDT 1991 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(91)90138-U· OSTI ID:6005408

Ruffet, G ^[1]; Feraud, G ^[2]; Amouric, M ^[3]

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1. Univ. de Rennes (France)
2. Univ. de Nice-Sophia Antipolis, Nice (France)
3. Centre National de la Recherche Scientifique, Marseille (France)

Bulk samples and single grains of biotites from the North Tregor Batholite (Armorican Massif, France) were analyzed by the {sup 40}Ar/{sup 39}Ar method. Apparently pure, single biotite grains, analyzed by the step heating procedure with the laser probe, displayed plateau ages or slightly disturbed age spectra. One strongly chloritized single biotite grain gave a very disturbed age spectrum with younger ages. The bulk samples of biotites of the same rocks displayed disturbed age spectra characterized by younger low temperature ages and a hump at intermediate temperature steps. These disturbances are explained by {sup 39}Ar recoil from the biotite into the chlorite which is clearly evidenced by HRTEM observations, and not by excess {sup 40}Ar. The more concordant results obtained on single biotites are probably due to a more careful selection of the minerals. In most cases, we obtain good concordance of the ages (600 - 610 Ma) measured on the apparently pure, single biotite grains and the high temperature ages of both the bulk samples of amphiboles and biotites from the same rocks.

• OSTI ID: 6005408
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Journal Name: Geochimica et Cosmochimica Acta; (United States) Vol. 55:6; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
AGE ESTIMATION
AMPHIBOLE
ARGON 39
ARGON 40
ARGON ISOTOPES
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BIOTITE
CHEMISTRY
COMPARATIVE EVALUATIONS
DEVELOPED COUNTRIES
ELECTRON MICROSCOPY
EUROPE
EVALUATION
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
FRANCE
GEOCHEMISTRY
HYDROTHERMAL ALTERATION
IGNEOUS ROCKS
ISOTOPE DATING
ISOTOPE RATIO
ISOTOPES
LASER SPECTROSCOPY
LIGHT NUCLEI
MICA
MICROSCOPY
MINERALS
NUCLEI
PLUTONIC ROCKS
RADIOISOTOPES
ROCKS
SILICATE MINERALS
SPECTROSCOPY
STABLE ISOTOPES
TRANSMISSION ELECTRON MICROSCOPY
X-RAY SPECTROSCOPY
YEARS LIVING RADIOISOTOPES