Suites of granitoid rocks and acidic volcanics constitute the greater part of the Precambrian basement in Suriname. A Rb-Sr whole-rock isochron analysis on 32 samples (14 plutonic, 17 volcanic, and 1 pegmatite) yields an age of 1810 ± 40 m.y. (λ120 = 1.47 X 10-11/yr, error with 95 percent confidence level) placing this episode of magmatic activity within the Trans-Amazonian Orogenic cycle. Rb-Sr and K-Ar measurements on micas show that the western part of Suriname and the neighboring southern part of Guyana were affected by a tectonothermal event about 1200 ±100 m.y. ago, the Nickerie Metamorphic Episode.

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