Abstract

The 40Ar/ 39Ar apparent ages found by Qiu and Wijbrans [Qiu, H.N. and Wijbrans, J.R., 2008. The Paleozoic metamorphic history of the Central Orogenic Belt of China from 40Ar/ 39Ar geochronology of eclogite garnet fluid inclusions. Earth Planet. Sci. Lett., 268, 501–514. doi: 10.1016/j.epsl.2008.01.042; Qiu, H.N. and Wijbrans, J.R., 2006. Paleozoic ages and excess 40Ar in garnets from the Bixiling eclogite in Dabieshan, China: new insights from 40Ar/ 39Ar dating by stepwise crushing. Geochim. Cosmochim. Acta, 70, 2354–2370. doi: 10.1016/j.gca.2005.11.030.] for crushing in vacuo experiments on Dabieshan eclogite garnets are best explained by a simple mixing model with radiogenic 40Ar ⁎ and air argon for the final plateau data, and excess 40Ar released in the initial crushing steps. More intricate models such as the hypothesized mixture of phengite, K-feldspar, amphibole and omphacite solid impurities by Kendrick [Kendrick, M.A., 2007. 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’. Geochim. Cosmochim. Acta, 71, 6040–6045. doi: 10.1016/j.gca.2007.01.029.] and Kendrick and Phillips [Kendrick, M.A. and Phillips, D., 2009. Discussion of ‘The Paleozoic metamorphic history of the Central Orogenic Belt of China from 40Ar/ 39Ar geochronology of eclogite garnet fluid inclusions by Qiu Hua-Ning and Wijbrans J.R.’. Earth Planet. Sci. Lett.] cannot explain the consistently observed 40Ar/ 39Ar age plateaux and isochrons because mixing of more than two K-containing end members each with different ages, different initial 40Ar/ 36Ar ratios and different proportional argon release patterns cannot define an isochron and age plateau, and the solid inclusion mixing model fails to address the consistently observed correlation between the radiogenic signal and chlorine derived 38Ar.

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