The crystal-chemical basis for Ar retention in micas: inferences from interlayer partitioning and implications for geochronology

Article Abstract:

The crystal-chemical analysis of micas shows that (super 40)Ar retention is less in biotite than in muscovite. The partitioning behavior of biotite and muscovite shows that the weaker interlayer bonding in biotite is due to spacious interlayer volume and fewer interlayer bonds per unit cell. Muscovite gives a more favorable electrostatic environment for Ba(super 2+) substitution than biotite. The interlayer ionic porosity affects the loss of radiogenic isotopes. The partitioning/porosity studies help geochronological predictions.

Muscovite, Biotite, Mineralogical chemistry

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Multipath diffusion in geochronology

Article Abstract:

Ion and laser microprobe analytical tools reveal spatial distributions of radiogenic isotopes in minerals not detected by simple volume diffusion. A numerical model for solving coupled multi-path diffusion equations, which describe simultaneous diffusion of a solute species through the crystal lattice and high-diffusivity pathways under non-steady conditions, has been developed. Adding a radioactive source term to the equations provides lower integrated cooling ages and closure temperatures.

Earth, Thermal diffusivity, Earth's age

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(super 40)Ar-(super 39)Ar and Rb-Sr geochronology of high-pressure metamorphism and exhumation history of the Tavsanli Zone, NW, Turkey

Article Abstract:

An analysis of the metamorphism of argon is presented, focusing on problems created by excess argon. Topics include techniques of geochronology, uncovering the history of high-pressure low-temperature rocks, and use of infrared lasers to analyze phengite grains.

Turkey, Statistical Data Included, Analysis, Isotopes, Argon, Infrared equipment, Metamorphism (Geology)

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