Were Amazonia and Baltica Connected in Nuna and Rodinia?

Abstract:

Most of paleogeographic reconstructions of Proterozoic supercontinents Rodinia and Nuna consider a long-lived connection between Baltica and Amazonia/West Africa between 1.8 and 1.0 Ga. This connection implies a common Paleo-to-Mesoproterozoic accretionary margin of south-western Baltica and Amazonia. We tested the validity of this hypothesis by the time-space analysis of the crustal growth of major tectonic domains in these cratons and their possible relationships. We analysed a subduction polarity, gaps in juvenile crustal growth, “stitching” magmatism and sedimentary basins as well as SLIP and LIP events. In doing so, we found several mismatches between respective domains of these cratons: (a) their chronologies and “barcodes” of magmatism are mostly non-correlative; (b) their subduction directions were different, e. g. at 2.0-1.90, 1.80-1.75, and 1.0 Ga; (c) accretionary crustal growth of Baltica was semi-continuous during 500 m. y. (2.0 to1.5 Ga), while in Amazonia production of juvenile crust occurred in relatively short, 100-200 m.y. periods (2.0-1.9 and 1.55-1.35 Ga) with 100-150 m. y. gaps; (d) subduction stopped in Baltica between 1.45 and 1.2 Ga but continued in Amazonia at the same time; (e) some parts of Amazonian provinces could be incorporated microcontinents like Rio Negro(?) and Paragua; (f) Baltica escaped the 1.89-1.87 Ga SLIP and 1.8-1.75 Ga LIP events, which broadly disturbed Amazonia. Several apparently coeval periods of crustal growth and tectonism in Amazonia and Baltica (1.8-1.75, 1.59-1.52, 1.50-1.40, 1.1-0.95Ga) we interpret as indicators of global plate reorganization and continent rotations. Careful analysis of available Mesoproterozoic paleomagnetic data from Baltica and Amazonia also does not support a long-lived integrity of these cratons.