THE SR AND ND ISOTOPE GEOLOGY AND GLOBAL GEODYNAMICS AT THE 2.5 GA BOUNDARY

Abstract

Isotopic signatures of the lower and upper continental crust and basalts from oceans and continents have been systematically arranged on a plot in the coordinates of Sr-Nd isotope ratios. Both mantle trends of isotopic systems demonstrate a drastic change in geodynamic at the 2.5 Ga boundary, which most probably can be regarded as the only temporal and geodynamic boundary on the global scale. This boundary is revealed in all continents as the first distinct unconformable overlapping of high-grade Catarchean and Paleoproterozoic gray gneiss (TTG) and basalt-komatiite complexes by slightly metamorphosed Mesoproterozoic volcanogenic terrigenous sequences. Thus, the global manifestation, geodynamic position, and isotopic significance of the 2.5 Ga boundary indicate that this interval marks the replacement of the exoplanetary (cosmic) geodynamic stage by the endoplanetary geodynamic stage of intense differentiation. This shows a nonlinear and irreversible evolution of the Earth as a self-organizing dissipative system.