Argon release mechanisms of biotite in vacuo and the role of short-circuit diffusion and recoil

The Meso-Cenozoic thermo-tectonic evolution of the Eastern Pyrenees: an 40Ar/39Ar fission track and (U–Th)/He thermochronological study of the Canigou and Mont-Louis massifs

“…For this sample, electron microprobe analyses indicate a higher Mg content compared to other biotites from this massif (Maurel 2003), which may imply a higher retentivity for radiogenic argon (Harrison et al 1985;Dahl 1996). The preservation of a core-rim age zoning in biotite, similar to that observed in muscovite, confirms the fact that the step-heating procedure tends to average the isotopic gradients (Lo et al 2000) resulting from slow cooling (Hodges and Bowring 1995) or thermal overprinting (Hames and Cheney 1997). Given the present geological context, thermal overprinting in Alpine (Morris et al 1998;Sère 1993).…”

Rb–Sr and K–Ar systems of biotite in surface environments regulated by weathering processes with implications for isotopic dating and hydrological cycles of Sr isotopes

“…In both spectra, gradual increase in age toward higher-temperature degassing steps correlates well with the theoretical age spectra based on diffusion theory (Turner, 1968). It has been disputed whether 40 Ar-39 Ar age spectra of biotite from the vacuum stepwise extraction provide information on a natural gradient of 40 Ar formed by diffusion during the geological events such as contact metamorphism (Hanson et al, 1975;Ozima et al, 1979;Harrison et al, 1985;Gaber et al, 1988;Lo et al, 2000). Most studies concluded that initial 40 Ar distribution is lost by the significant structural, chemical, and morphological changes of biotite during the heating, resulting in the perturbed or flat age spectra regardless of the initial gradient (Hanson et al, 1975;Harrison et al, 1985;Gaber et al, 1988;Lo et al, 2000).…”

“…It has been disputed whether 40 Ar-39 Ar age spectra of biotite from the vacuum stepwise extraction provide information on a natural gradient of 40 Ar formed by diffusion during the geological events such as contact metamorphism (Hanson et al, 1975;Ozima et al, 1979;Harrison et al, 1985;Gaber et al, 1988;Lo et al, 2000). Most studies concluded that initial 40 Ar distribution is lost by the significant structural, chemical, and morphological changes of biotite during the heating, resulting in the perturbed or flat age spectra regardless of the initial gradient (Hanson et al, 1975;Harrison et al, 1985;Gaber et al, 1988;Lo et al, 2000). However, the weathered biotites (A4 and A7) in this study were already oxidized in the weathering profile and underwent chemical and structural changes.…”

High-strain deformation and fluid infiltration diachronism of the middle crust: New Devonian–Permian Alice Springs ages (365–290 Ma) of shear zones in the Strangways Metamorphic Complex, Central Australia

“…A comparison of Table 4 Roddick et al, 1980;Foland, 1983) implying that the 40 Ar E can be uniformly distributed throughout the mica structure, or alternatively, the biotite underwent structural decomposition in vacuo during stepheating (e.g. Lo et al 2000). The differential uptake (partitioning) of 40 Ar E between coexisting biotite and muscovite is an enigmatic phenomenon which has been reported in the literature but remains unexplained (e.g.…”