Diffusion of helium isotopes in silicate glasses and minerals: Implications for petrogenesis and geochronology. Doctoral thesis

Technical Report · Thu Jun 01 04:00:00 EDT 1989

OSTI ID:6645898

Trull, T W

Helium diffusivities in basaltic glasses at seafloor temperatures are about 10 to the -16th power sq cm/s suggesting only very low concentration samples will be compromised, and that U/He geochronology of submarine basalts may be feasible. Helium diffusivities at magmatic temperatures are 10 to the -11th power, to 10 to the -8th power sq cm/s in silicate minerals, too low to regionally homogenize helium in the mantle. Helium exchange rates limit xenolith origin depths and transport times. Faster He diffusion in pyroxene than olivine allows diffusive loss to be evaluated. Diffusivities of {sup 3}He produced by cosmic rays in surface rocks are less than 10 to the -20th power sq cm/s in olivine and quartz, suggesting exposure dating will not be limited by helium loss for ages up to 10,000,000 years. Similar conclusions were found for U/{sup 4}He dating of quartz. Part of the {sup 3}He/{sup 4}He variability (.01 to 9 R{sub a}) of island arc basalts from the western Pacific reflects post-eruptive helium addition. In unaltered samples, Kavachi submarine volcano has different {sup 3}He/{sup 4}He (6.9 + or - .2 R{sub a}) than the Woodlark Spreading Center (8-9 R{sub a}). A contribution from subducted Pacific lithosphere may explain this and 87 Sr/86 Sr variations.

• Research Organization: Woods Hole Oceanographic Institution, MA (USA)
• OSTI ID: 6645898
• Report Number(s): PB-90-241738/XAB; WHOI--89-15
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
AGE ESTIMATION
BASALT
CHEMISTRY
DIFFUSION
GEOCHEMISTRY
GEOLOGIC SURVEYS
GEOLOGY
GLASS
HELIUM ISOTOPES
IGNEOUS ROCKS
ISOTOPE DATING
ISOTOPE RATIO
ISOTOPES
MECHANICS
OXYGEN COMPOUNDS
PACIFIC OCEAN
PETROGENESIS
PETROLOGY
ROCK MECHANICS
ROCKS
SEA BED
SEAS
SILICATES
SILICON COMPOUNDS
SURFACE WATERS
SURVEYS
VOLCANIC ROCKS
VOLCANOES