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’

New constraints on the release of noble gases during in vacuo crushing and application to scapolite Br–Cl–I and 40Ar/39Ar age determinations

“…5 and 6) is consistent with shorter experiments that have demonstrated minor release of He and Ar from olivine, clinopyroxene and mica matrices of both irradiated and unirradiated samples (Gusev et al, 1969;Scarsi, 2000;Dunlap and Kronenberg, 2001;Yokochi et al, 2005). The release of lattice-hosted noble gases is also consistent with the suggested release of Ar from mineral impurities during prolonged crushing of garnet (see Kendrick, 2007;Kendrick and Phillips, 2009). Therefore, it seems likely that similar release of lattice-hosted noble gases should be expected during prolonged in vacuo crushing of a variety of minerals.…”

“…These data confirm that in vacuo crushing can be used to selectively analyse fluid inclusions, but also indicate that the duration of in vacuo crushing experiments undertaken to analyse fluid inclusions should be limited (Kendrick, 2007;Kendrick and Phillips, 2009).…”

“…Scapolite is an obvious candidate for detailed investigation by this technique; however, our early attempts to outgas this mineral by conventional stepped heating experiments demonstrated significant fractionation of the noble gases (below). The present investigation was initiated after the publication of 40 Ar/ 39 Ar ages obtained by in vacuo crushing garnets Wijbrans, 2006, 2008), suggested significant quantities of lattice-hosted noble gas could be released during prolonged in vacuo crushing experiments (Kendrick, 2007;Kendrick and Phillips, 2009). In contrast, only minor release of He and Ar, from olivine, clinopyroxene and mica matrices, has been demonstrated by in vacuo crushing studies previously (e.g.…”

“…Hilton et al, 1993;Kendrick et al, 2001b;Matsumoto et al, 2001). Therefore, constraining the extent to which matrix-hosted noble gases could be released by in vacuo crushing, has implications for the design of experiments used to analyse fluid inclusions, as well as the interpretation of existing 40 Ar/ 39 Ar data (Kendrick, 2007;Kendrick and Phillips, 2009). …”

Linking continental deep subduction with destruction of a cratonic margin: strongly reworked North China SCLM intruded in the Triassic Sulu UHP belt

“…From the Qinling segment, Jian et al (2000) presented Early Paleozoic zircon U-Pb ages for eclogites and interpreted them as the time of eclogite recrystallization, but later studies have interpreted these ages as reflecting magmatic crystallization rather than metamorphism Liu et al 2004bLiu et al , 2006. In the Dabie belt, Qiu and Wijbrans (2006) obtained similar 39 Ar/ 40 Ar ages on inclusions in garnets from the Bixiling eclogites, but the result has been criticized by Kendrick (2007) and Zhao and Gao (2007) for the consideration of the existence of excess argon. In the Sulu belt, Yang et al (2005) reported a zircon U-Pb age of 445 ± 4 Ma for an eclogite from the Qinglongshan locality (Fig.…”