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Esboço geológico-tectônico do Cráton Guianês

1976; Sociedade Brasileira de Geologia; Volume: 6; Issue: 4 Linguagem: Inglês

10.5327/rbg.v6i4.103

2317-4889

Raimundo Montenegro Garcia de Montalvao,

Geological and Geochemical Analysis

Of all units which comprise the Guyana Craton, the Guianense Complex is the lowest, with portion of it named Rio Novo Granodiorite and Tumucumaque Gneiss. Capping the Guianense Complex, in angular unconformity, are the metasediments of the Vila Nova, Cauarane and Tunui Groups (2,100-1,800 m.y.). There were some magmatic effusione, both acidic and intermediate in composition, during the period of tectonic calm, in association with their subvolcanic equivalents. Such igneous cycle is named Uatuma Group (1,900-1,400 m.y.) with the Surumu and Iricoume formations, and the plutonic ones, known as Mapuera Granite, Serra do Mel Granite, Falsino Granodiorite, Surucucu Granite, Tiquie Granite, Erepecuru Syenite, and Cachorro Syenite. After the close of that almost craton period, the area passed through a period of block faulting producing basin or basins, which received thick sequences of sedimentary deposits, named Roraima Group (1,805 m.y.) and Sete Quedas Formation. At the end or even during the sedimentation, tholeiitic intrusions invaded the sedimentary rocks forming sills, dykes and stocks; they are known as Pedra Preta Diabase (1,805-1,600 m.y.), Suretama Gabbro (1,420 m.y.] and alkaline intrusions, (Mapari Syenite, 1,600-1,300 m.y.). After the close of this volcanism, the area was cratonized. As the cratonization was reached, tectomagmatic ativation and reativation events were produced, resulting rifts and intensive regional cataclasis accompanied by volcanism. Such events have received several denominations such as Nickerie-K'Mudku Orinoquiense or Jari-Falsino (1,200-1,000 m.y.), Cassipore Event (250-180 m.y.) or Takutu (200 m.y.), and the Apoteri tholeiitic volcanism (180-150 m.y.) and the Catrimani Syenite (100 m.y.). Late Cretaceous the Guianense Craton was affected by vertical movements, with deposition of continental clastic material, reaching even the Quaternary.