Argon diffusion in Apollo 16 impact glass spherules: Implications for 40Ar/39Ar dating of lunar impact events

David J. Gombosi, Suzanne L. Baldwin, E. Bruce Watson, Timothy D. Swindle, John W. Delano, Wayne G. Roberge

Research output: Research - peer-reviewArticle

  • 5 Citations

Abstract

The 40Ar/39Ar technique applied to impact glass has been used to date both terrestrial and lunar impact events. The ability to utilize the 40Ar/39Ar technique rests on the assumption that impact glasses are closed to the loss of daughter product, 40Ar*, after formation. Diffusion experiments were performed on three Apollo 16 lunar impact glasses and yielded activation energies for 39Ar of ~17 to 20kcalmol-1 and log10(D0/a2) values of -5.2 to -6.0 s-1. The resulting diffusion coefficients are interpreted as minimum values and the Apollo 16 glass is probably some of the least retentive of lunar glasses, as the degree of non-bridging oxygen is at one end of the range in lunar glasses. At temperatures below the glass transition temperature (i.e., ~660°C), the data can be explained by volume diffusion from a single diffusion domain. Modeling shows that Apollo 16 composition glass could lose significant quantities of radiogenic argon (40Ar*) (~90-100% over 20-40Myr assuming a diffusion domain size (a) of 75μm) due to diurnal temperature variations on the lunar surface, although 40Ar* loss is highly sensitive to exposure duration and effective diffusion domain size. Modeling shows that loss from transient thermal events (e.g., heating to ~200°C for 102yr duration) can also cause partial resetting of apparent 40Ar/39Ar ages. In small (a=75μm) glasses a maximum of 50-60% of 40Ar* is lost over 4Ga when buried to depths corresponding to temperatures of -15°C. Results indicate that caution should be exercised in interpreting lunar impact glass 40Ar/39Ar ages, as the assumption of closed system behavior may have been violated, particularly in glasses with low fractions of non-bridging oxygen.

LanguageEnglish (US)
Pages251-268
Number of pages18
JournalGeochimica et Cosmochimica Acta
Volume148
DOIs
StatePublished - Jan 1 2015

Fingerprint

spherule
argon
glass
dating
Argon
Glass
temperature
Temperature
loss
Oxygen
oxygen
modeling
Activation energy
Heating
Chemical analysis
Experiments
Glass transition temperature
Hot Temperature
argon isotope
resetting

ASJC Scopus subject areas

  • Geochemistry and Petrology

Cite this

Argon diffusion in Apollo 16 impact glass spherules : Implications for 40Ar/39Ar dating of lunar impact events. / Gombosi, David J.; Baldwin, Suzanne L.; Watson, E. Bruce; Swindle, Timothy D.; Delano, John W.; Roberge, Wayne G.

In: Geochimica et Cosmochimica Acta, Vol. 148, 01.01.2015, p. 251-268.

Research output: Research - peer-reviewArticle

Gombosi, David J. ; Baldwin, Suzanne L. ; Watson, E. Bruce ; Swindle, Timothy D. ; Delano, John W. ; Roberge, Wayne G./ Argon diffusion in Apollo 16 impact glass spherules : Implications for 40Ar/39Ar dating of lunar impact events. In: Geochimica et Cosmochimica Acta. 2015 ; Vol. 148. pp. 251-268
@article{b44e197f4dc644e4be902660128f0605,
title = "Argon diffusion in Apollo 16 impact glass spherules: Implications for 40Ar/39Ar dating of lunar impact events",
abstract = "The 40Ar/39Ar technique applied to impact glass has been used to date both terrestrial and lunar impact events. The ability to utilize the 40Ar/39Ar technique rests on the assumption that impact glasses are closed to the loss of daughter product, 40Ar*, after formation. Diffusion experiments were performed on three Apollo 16 lunar impact glasses and yielded activation energies for 39Ar of ~17 to 20kcalmol-1 and log10(D0/a2) values of -5.2 to -6.0 s-1. The resulting diffusion coefficients are interpreted as minimum values and the Apollo 16 glass is probably some of the least retentive of lunar glasses, as the degree of non-bridging oxygen is at one end of the range in lunar glasses. At temperatures below the glass transition temperature (i.e., ~660°C), the data can be explained by volume diffusion from a single diffusion domain. Modeling shows that Apollo 16 composition glass could lose significant quantities of radiogenic argon (40Ar*) (~90-100% over 20-40Myr assuming a diffusion domain size (a) of 75μm) due to diurnal temperature variations on the lunar surface, although 40Ar* loss is highly sensitive to exposure duration and effective diffusion domain size. Modeling shows that loss from transient thermal events (e.g., heating to ~200°C for 102yr duration) can also cause partial resetting of apparent 40Ar/39Ar ages. In small (a=75μm) glasses a maximum of 50-60% of 40Ar* is lost over 4Ga when buried to depths corresponding to temperatures of -15°C. Results indicate that caution should be exercised in interpreting lunar impact glass 40Ar/39Ar ages, as the assumption of closed system behavior may have been violated, particularly in glasses with low fractions of non-bridging oxygen.",
author = "Gombosi, {David J.} and Baldwin, {Suzanne L.} and Watson, {E. Bruce} and Swindle, {Timothy D.} and Delano, {John W.} and Roberge, {Wayne G.}",
year = "2015",
month = "1",
doi = "10.1016/j.gca.2014.09.031",
volume = "148",
pages = "251--268",
journal = "Geochmica et Cosmochimica Acta",
issn = "0016-7037",
publisher = "Elsevier Limited",

}

TY - JOUR

T1 - Argon diffusion in Apollo 16 impact glass spherules

T2 - Geochmica et Cosmochimica Acta

AU - Gombosi,David J.

AU - Baldwin,Suzanne L.

AU - Watson,E. Bruce

AU - Swindle,Timothy D.

AU - Delano,John W.

AU - Roberge,Wayne G.

PY - 2015/1/1

Y1 - 2015/1/1

N2 - The 40Ar/39Ar technique applied to impact glass has been used to date both terrestrial and lunar impact events. The ability to utilize the 40Ar/39Ar technique rests on the assumption that impact glasses are closed to the loss of daughter product, 40Ar*, after formation. Diffusion experiments were performed on three Apollo 16 lunar impact glasses and yielded activation energies for 39Ar of ~17 to 20kcalmol-1 and log10(D0/a2) values of -5.2 to -6.0 s-1. The resulting diffusion coefficients are interpreted as minimum values and the Apollo 16 glass is probably some of the least retentive of lunar glasses, as the degree of non-bridging oxygen is at one end of the range in lunar glasses. At temperatures below the glass transition temperature (i.e., ~660°C), the data can be explained by volume diffusion from a single diffusion domain. Modeling shows that Apollo 16 composition glass could lose significant quantities of radiogenic argon (40Ar*) (~90-100% over 20-40Myr assuming a diffusion domain size (a) of 75μm) due to diurnal temperature variations on the lunar surface, although 40Ar* loss is highly sensitive to exposure duration and effective diffusion domain size. Modeling shows that loss from transient thermal events (e.g., heating to ~200°C for 102yr duration) can also cause partial resetting of apparent 40Ar/39Ar ages. In small (a=75μm) glasses a maximum of 50-60% of 40Ar* is lost over 4Ga when buried to depths corresponding to temperatures of -15°C. Results indicate that caution should be exercised in interpreting lunar impact glass 40Ar/39Ar ages, as the assumption of closed system behavior may have been violated, particularly in glasses with low fractions of non-bridging oxygen.

AB - The 40Ar/39Ar technique applied to impact glass has been used to date both terrestrial and lunar impact events. The ability to utilize the 40Ar/39Ar technique rests on the assumption that impact glasses are closed to the loss of daughter product, 40Ar*, after formation. Diffusion experiments were performed on three Apollo 16 lunar impact glasses and yielded activation energies for 39Ar of ~17 to 20kcalmol-1 and log10(D0/a2) values of -5.2 to -6.0 s-1. The resulting diffusion coefficients are interpreted as minimum values and the Apollo 16 glass is probably some of the least retentive of lunar glasses, as the degree of non-bridging oxygen is at one end of the range in lunar glasses. At temperatures below the glass transition temperature (i.e., ~660°C), the data can be explained by volume diffusion from a single diffusion domain. Modeling shows that Apollo 16 composition glass could lose significant quantities of radiogenic argon (40Ar*) (~90-100% over 20-40Myr assuming a diffusion domain size (a) of 75μm) due to diurnal temperature variations on the lunar surface, although 40Ar* loss is highly sensitive to exposure duration and effective diffusion domain size. Modeling shows that loss from transient thermal events (e.g., heating to ~200°C for 102yr duration) can also cause partial resetting of apparent 40Ar/39Ar ages. In small (a=75μm) glasses a maximum of 50-60% of 40Ar* is lost over 4Ga when buried to depths corresponding to temperatures of -15°C. Results indicate that caution should be exercised in interpreting lunar impact glass 40Ar/39Ar ages, as the assumption of closed system behavior may have been violated, particularly in glasses with low fractions of non-bridging oxygen.

UR - http://www.scopus.com/inward/record.url?scp=84918579439&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84918579439&partnerID=8YFLogxK

U2 - 10.1016/j.gca.2014.09.031

DO - 10.1016/j.gca.2014.09.031

M3 - Article

VL - 148

SP - 251

EP - 268

JO - Geochmica et Cosmochimica Acta

JF - Geochmica et Cosmochimica Acta

SN - 0016-7037

ER -