Abstract
Analysis of recent geological and geochronological data from the basement of the South American platform indicates that the Brasiliano orogenic collage took place in four distinct pulses: a) Early Cryogenian (ca. 800 - 740Ma); b) Late Cryogenian-Early Ediacaran (ca. 660 - 610 Ma); c) Early-Middle Ediacaran (c. 590 - 560 Ma); and d) Late Cambrian (520 - 500 Ma). The first three pulses are well represented in most Neoproterozoic structural provinces in West Gondwana. The youngest orogenic phase/pulse, however, is only seen in Argentina (Pampean Orogeny) and Brazil, in eastern Rio de Janeiro State (Búzios Orogeny). The period between ca. 750 and 500 Ma is comparable to that reported for the amalgamation of various continental fragments in East (Arabian-Nubian, Mozambique, Kuunga) and North Gondwana (Cadomian). However, important differences in the nature and ages of events are recognized, which can be expected in view of the magnitude of Gondwana agglutination and the diversity of paleogeographic and tectonic scenarios. West Gondwana shows an interesting peculiarity: lithologically and tectonically diversified Tonian terranes underlie Brasiliano orogenic buildups. They were strongly reworked during most of the orogenic pulses. The Tonian terranes (1000 - 900 Ma) and their relation with Rodinia or with the processes of Gondwana fusion remains an open question. Indications of their presence in East Gondwana are still poorly documented.
Highlights
Over the last five decades the word “Brasiliano” has been loosely used to refer to many aspects of the Neoproterozoic geology of Brazil.When the first formal definitions were proposed (Cordani et al 1968, Cordani et al 1973, Almeida et al 1973; Almeida e Hasui 1984), the term appeared as “Brasiliano cycle” (“Ciclo Brasiliano”), comprising the period from 700 to 450 Ma
These authors separated it from the pre-Neoproterozoic cycles, defined in the early 70s(e.g. the “Uruaçuano”, “Espinhaço”, and “Transamazonian” cycles)
These seminal concepts were heavily based on Rb-Sr and K-Ar geochronology, the only methods available at that time
Summary
Over the last five decades the word “Brasiliano” has been loosely used to refer to many aspects of the Neoproterozoic geology of Brazil (e.g. cycle, orogeny, tectonic evolution, metamorphism, mobile belts, cratons, etc.). The poor dating was made worse by the non-uniform availability of the data over the South American territory These definitions were strongly biased by poor geological and geotectonic knowledge, associated to the need to establish the timing of geological/geotectonic processes in South America (see a synthesis of original definitions in Brito Neves et al 1990, and in Tab. 1). 1,300-1,100 Ma) proposal was consolidated in the same publication of Almeida et al (1973), it was present in several earlier studies, in other structural provinces of South America This was an interpretive mistake of geological and isotopic data (mostly Rb-Sr and K-Ar), which gradually disappeared from the scientific archive of the continent, due to the growth in the geological knowledge of the region. As mentioned above, Brito Neves et al (1990) presented a synthesis of these classifications and systematizations (Tab. 1)
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