Abstract
Of the four superposed tectonic units in the study area, the uppermost (Unit IV) is lithologically similar to the lowermost (Unit I). Both are formed dominantly by orthogneiss. In an earlier article, Bonev et al. (2010) had shown that the orthogneisses of units I and IV display similar trace element patterns and therefore interpreted Unit IV as an equivalent of Unit I emplaced by an overthrust on top of the other units. Our new U–Pb zircon dating, however, showed that the orthogneiss of Unit I was formed from a Late Carboniferous protolith, and the orthogneiss of Unit IV from a Neoproterozoic protolith. These rocks are of different ages, and their lithological and geochemical similarity is a mere coincidence. In their comment, Bonev et al. (2016) again demonstrate the geochemical similarity (their Fig. 1) and write that this “allows some caution to be expressed relative to the age of 581 Ma” determined by us. We do not share this opinion. On the contrary, we think that more caution would be necessary in interpreting geochemical data. To illustrate this, we show in Fig. 1 the compositions of the three orthogneisses that Bonev et al. (2016) show in their Fig. 1b (in order to demonstrate their similarity), together with the average composition of the upper continental crust (thick blue line) after Wedepohl (1995) and the composition of JG-1 (thick red line), a common granodiorite standard from Japan after Ando et al. (1971). The similarity between the patterns of the three Bulgarian orthogneisses is not larger than the similarity between any of them and the granodiorite from Japan, and all of them are similar to the average composition of the upper continental crust. These concentrations reflect fundamental differentiation of our planet and are not capable of fingerprinting a certain origin. Introduction
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