- © 2006 Geological Society of South Africa
Reimold et al.’s observations on Alexandre et al.(2006) concern the 40Ar/39Ar analytical data, their statistical treatment, and the suggested age interpretations, without commenting on the extensive and detailed structural data presented. Their criticisms can be divided into three categories: (a) not taking into account the recoil effects on the age calculation leads to erroneous ages; (b) the 40Ar/39Ar ages we suggest are in fact lower than the real crystallization ages, due to a suggested “bias” between 40Ar/39Ar and U/Pb ages; and (c) the metamorphism dated is not the result of the Transvaalide orogeny (Andreoli, 1988a), but of the Bushveld “metamorphic” episode. Reimold et al. also criticize our use of the top-of-the-bell ages and what they consider to be a non-rigorous approach in age calculation. In conclusion, Reimold et al. assert that our data are neither robust nor reliable and cannot be related to a discrete metamorphic event (the proposed Transvaalide orogeny: Andreoli, 1988a) that occurred at the time we suggest (2042.1 ± 2.9 Ma: Alexandre et al., 2006) Hereafter, we will answer their comments point by point.
Recoil effect on the calculated ages
Firstly, we would like to state that we have been very careful not to misrepresent our analytical data: we have thoroughly described the results obtained and commented about the validity of the calculated ages. The recoil effect observed in our samples TTW12 and P2 is very limited (Alexandre et al., 2006: Figure 6); it is more pronounced in sample PEL-PIK where it is combined with superficial 40Ar* loss, while sample TT3 exhibits a significant 40Ar* loss. However, we are not certain - and have never suggested - that the age spectra of samples PEL-37 and PEL-34B indicate unambiguously (or at all) 39ArK recoil; indeed, there …