Reply to comment by M. A. Kendrick and D. Phillips (2009) on 'The Paleozoic metamorphic history of the Central Orogenic Belt of China from ~(40)Ar/~(39)Ar geochronology of eclogite garnet fluid inclusions' by Hua-Ning Qiu and J. R. Wijbrans (2008) [Earth Planet. Sci. Lett. 268 (2008) 501-514]

摘要

The ~(40)Ar/~(39)Ar apparent ages found by Qiu and Wijbrans [Qiu, H.N. and Wijbrans, J.R,, 2008. The Paleozoic metamorphic history of the Central Orogenic Belt f 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 ~(40)Ar in garnets from the BiXiling eclogite in Dabieshan, China: new insights from ~(40)Ar/~(39)Ar dating by stepwise crushing. Geochim. Cosmochim. Acta, 70,2354-2370. doi: 10.1016/j.gca.2005.11.030.] for crushing in vacua experiments on Dabieshan eclogite garnets are best explained by a simple mixing model with radiogenic ~(40)Ar~* and air argon for the final plateau data, and excess ~(40)Ar 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 ~(40)Ar in garnets from the Bixiling eclogite in Dabieshan, China: new insights from ~(40)Ar/~(39)Ar 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 f China from ~(40)Ar/~(39)Ar geochronology of eclogite garnet fluid inclusions by Qiu Hua-Ning and Wijbrans J.R,'. Earth Planet. Sci. Lett.] cannot explain the consistently observed ~(40)Ar/~(39)Ar age plateaux and isochrons because mixing of more than two K-containing end members each with different ages, different initial ~(40)Ar/~(36)Ar 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.