Reply to comment by E. Martin, M. Martin, and O. Sigmarsson on 'Continental geochemical signatures in dacites from Iceland and implications for models of early Archaean crust formation' by M. Willbold, E. Hegner, A. Stracke, and A. Rocholl

摘要

By comparing the KCAD with early Archaean TTG we do not necessarily imply that the latter were formed in a geodynamic setting identical to that of Iceland. In contrast to the early Archaean (assuming that modern-style plate-tectonics had not been operating), the Iceland plateau does not remain stationary with respect to the deep reference system of the plume and thus the opportunity for crustal melting is limited. The interaction between the Iceland mantle plume and the Atlantic mid-ocean ridge system, however,makes Iceland unique among all oceanic plateaus or ocean island chains. The heat flow in the Icelandic crust is considerably higher than the average present-day global heat flux and resembles somewhat better the one in the early Archaean (e.g. see Bickle, 1978; Herzberg, 1992; Nisbett et al., 1993; Arndt et al., 1998). The excess heat drives large hydrothermal systems and facilitates intense hydratisation of the Icelandic crust. This stabilises amphibole, which, during progrademetamorphism, releases water and triggers dehydration melting. The high heat flow may also promote its melting (i.e. granitisation) as testified by the unusually high abundance of felsic volcanic rocks when compared to other modern oceanic plateaus (e.g. ?skarsson et al., 1982; Jónasson, 2007). As such, the processes that formed the KCAD in Iceland may indeed be interpreted as a modern analogue of early Archaean processes involved in the formation of Archaean TTG.