Abstract
A possible palaeogeographic link between the Grenville and Rondonia-Sunsas provinces is reinforced by the timing of thermometamorphic and plutonic events. Equivalent terms of regional geological time scales are: Ketilidian = Transamazonian; Palaeohelikian or Elsonian = Rondonian-San Ygnacio; Neohelikian or Grenvillian = Sunsas; Hadrynian = Brasiliano. Remobilization of the older crust is another feature common to both provinces in Helikian times. Felsic volcanics extruded 1650 million years ago in the eastern Grenville Province show 1.6 Ga analogues in the Roosevelt lava flows of the Amazon Craton. Also a recently defined 1470–1500 Ma Pinwarian event in the Grenville shows correlatives in the final stages of evolution of the Rio Negro-Juruena belt. Significant anorthosite-mangerite-charnokite-granite (AMCG) plutonism affected both regions during closely spaced periods of time. Two pulses of late potash-rich plutonism responsible for rapakivi intrusions from about 1.1 to 0.95 Ga are recognized in Grenvillia from Labrador to Texas and in the Rondonian-Sunsas Province of the Amazon Craton. Differences between the provinces include AMCG massifs of northeastern Laurentia whose equivalents in Rondonia are small layered mafic bodies, besides mangeritic/charnockitic intrusions and the large extensional and transtensional features of Sunsas age in the southwest Amazon sector. The AMCG plutonism roughly coeval with cratonic magmatism associated with transtensional features in the Amazon Craton allow two possible models to be postulated: (a) Amazonian transtensional features originated in response to collision with a left-lateral component, as along the Grenville front similar to the reactivation of the Asian continent due to the Himalayan push (diva basins and magmatism on the Sinian Platform); (b) major continental extensions related to the start of two Wilson cycles, one preceding the opening of a Grenvillian Ocean at around 1.4–1.3 Ga and, the other, due to the separation of Laurentia from Amazonia at the end of the Grenvillian cycle. Both have been related to extensive underplating.
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