Reconnaissance geochronology of basement rocks from the Amazonas and Maranhão Basins in Brazil |
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| Authors: | Adam Kovach Harold W Fairbairn Patrick M Hurley Miguel AS Basei Umberto G Cordani |
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| Institution: | Department of Earth and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Ma., U.S.A.;Geochronology Research Center, University of São Paulo, Brazil |
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| Abstract: | Rb/Sr whole rock as well as K/Ar whole rock and mineral age determinations have been carried out on drill core samples obtained from the crystalline basement underlying the Amazonas and Maranhão Basins in Brazil. The data confirm the existence of an ancient basement under the Upper and Middle Amazonas Basin. The primary age of the granitic rocks is estimated at about 1560 Ma which correlates with recent age data obtained on granitic rocks on both sides of the Amazonas syneclise. In some areas the K/Ar ages show a decrease probably due to the effect of the Nickerie thermal episode described previously in the Guayana Shield.In the basement of the interconnected Lower Amazonas and Maranhão Basins Late Precambrian (Caririan) metamorphism and igneous activity seems to have been pervasive. The data allow the continuation of the Brazilian age province known in northeastern Brazil under the Maranhão Basin, linking this province to the Brasilia-Paraguay orogenic belt of similar age. |
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