Argon loss during deformation of micas: constraints from laboratory deformation experiments

Paleozoic ages and excess 40Ar in garnets from the Bixiling eclogite in Dabieshan, China: New insights from 40Ar/39Ar dating by stepwise crushing

“…Crushing apparently has very little effect on the gas component that is trapped within the crystal lattice: the crushing experiment on the Methuen muscovite (Dunlap and Kronenberg, 2001) showed that only $0.53% of total 39 Ar was released by crushing. Qiu et al (2002a) indicated that ''strong differences between the results of the crushing and heating experiments of two samples imply that the gases released by crushing were mainly from the fluid inclusions and those by heating were from the mineral component of the samples, which was supported by microscopic observations of the thin sections and the results of EPMA and XRD analyses'' and ''the gases within the structures of the solid minerals are hardly released by crushing.''…”

Comment on ‘Paleozoic ages and excess 40Ar in garnets from the Bixiling eclogite in Dabieshan, China: New insights from 40Ar/39Ar dating by stepwise crushing by Hua-Ning Qiu and J.R. Wijbrans’

“…Crushing released 2.5% of the total 39 Ar from an Fe-mica compared to the figure of 0.53% for Methuen muscovite cited by Qiu and Wijbrans (2006) (see Dunlap and Kronenberg, 2001). Furthermore, crushing released measurable Ar from both samples yielding scattered apparent ages close to, or higher than, the ages determined by stepped heating (Dunlap and Kronenberg, 2001).…”

“…The study of Dunlap and Kronenberg (2001) referred to by Qiu and Wijbrans (2006) demonstrated that 39 Ar can be extracted from some mica samples by in vacuo crushing. Crushing released 2.5% of the total 39 Ar from an Fe-mica compared to the figure of 0.53% for Methuen muscovite cited by Qiu and Wijbrans (2006) (see Dunlap and Kronenberg, 2001).…”

Thermochronology in Orogenic Systems

“…Many deformed rocks display multiple generations of tectonite fabrics, and techniques such as laser microprobe 40 Ar/ 39 Ar dating of polished thin sections permit the dating of specific minerals in structural context and, thus, determination of the absolute ages of different fabric-forming events. Although care must be taken to ensure that the dates for older grains are not compromised by deformation-induced loss of radiogenic 40 Ar (Dunlap and Kronenberg, 2001;Kramar et al, 2001;Mulch et al, 2002;Reddy and Potts, 1999), some successful studies have been carried out (e.g., Chan et al, 2000;Di Vincenzo et al, 2001;Hames and Cheney, 1997;Mulch and Cosca, 2004;Mulch et al, 2005b). This approach ultimately may prove to be particularly valuable for the study of the duration of and interval between fabric-forming events during orogenesis.…”