The Paleoproterozoic in the South-American continent: Diversity in the geologic time

The Paleoproterozoic blocks and terranes that constiture of the South-American continent basement register rock-forming events (orogeny and taphrogeny) clustered in the four different periods as defined by the International Stratigraphic Chart (IUGS/UNESCO 2004). There are some particular cases for which rifting and drifting events precede the processes of convergent interaction between lithospheric plates, representing therefore examples of Wilson Cycles. In other cases, the records of extensional processes and those of convergent interaction of lithospheric plates (orogenies) are either concurrent in time (with difficult discrimination between them) or concurrent in the geographic-geologic space (they occur in different and separated domains), privileging different regions. The four periods of rock-forming events discussed here (Siderian, Rhyacian, Orosirian, Statherian) are mainly recorded and recognizable for most of the cratonic domains of the continent, but they are gradually being identified within the Paleoproterozoic basement blocks (”inliers”) in the large Neoproterozoic (Brasiliano) provinces of the continent. In the latter, such discrimination is much more difficult due to the overprint of the Brasiliano thermo-dynamic processes. For many years (in the recent past), the word “Transamazonian” (event, orogeny, cycle) had been used to cover indiscriminately all these many different Paleoproterozoic events, of the four different periods. With the present discrimination of the four major stages (periods) on time of rock-forming processes (igneous, metamorphic and sedimentary assemblages) the term Transamazonian has naturally become obsolete, and its usage is no longer advisable.

► The Precambrian basement of the South American continent displays rock assemblages of all Paleoproterozoic periods.
► The Rhyacian period is the best well documented, in cratonic domains and in the basement of the Proterozoic fold belts.
► Some occurrences of Siderian rock assemblages are remarkable, mostly presenting high grade rock assemblages.
► Intraplate activities were predominant during the Statherian. Just one accretionary mobile belt is worthy of mention.