Palaeoproterozoic (~1.89 Ga) felsic volcanism of the Iricoumé Group, Guyana Shield, South America: geochemical and Sm-Nd isotopic constraints on sources and tectonic environment

• Published in: International geology review Vol. 56; no. 11; pp. 1332 - 1356
• Main Authors: Barreto, Carla Joana Santos, Lafon, Jean Michel, da Rosa Costa, Lúcia Travassos, Lima, Evandro Fernandes
• Format: Journal Article
• Language: English
• Published: Philadelphia Taylor & Francis 18.08.2014; Taylor & Francis Ltd
• Subjects: Amazonian Craton; geochronology; Iricoumé Group; Orosirian; volcanic rocks
• ISSN: 0020-6814; 1938-2839
• DOI: 10.1080/00206814.2014.930800

Hypabyssal and explosive volcanic rocks of the Iricoumé Group crop out in the Western Erepecuru-Trombetas Domain, in the Central Amazonian Province, south of the Guyana Shield. They are part of an extensive volcano-plutonic event, which marked the central part of the Amazonian Craton during the Orosirian. These volcanic rocks, formed at approximately 1.89 Ga, consist of pyroclastic rocks (ignimbrites, rheoignimbrites, surge-related lapilli-tuff, co-ignimbrite fall tuff) and subordinate felsic hypabyssal rocks. An older episode, with an age of approximately 1.99 Ga, occurs locally and is represented by latitic lava flows and spessartitic lamprophyres. The geochemical characteristics of the Iricoumé volcanic rocks suggest that they formed in a post-orogenic tectonic setting, while those of the older Orosirian magmatism suggest a subduction-related geodynamic setting. T DM model ages ranging from 2.18 to 2.39 Ga and slightly negative ε Nd(T) values for most of the Iricoumé volcanic rocks indicate dominant Rhyacian crustal sources for the parental magmas. The positive ε Nd(T) values exhibited by some Iricoumé rhyolites (T DM : 1.98 and 2.06 Ga) and by the 1.99 Ga lava flows and lamprophyre (T DM : 2.13 and 2.21 Ga) suggest a juvenile mantle source, although a minor contribution of Palaeoproterozoic crust cannot be ruled out. These new results furnish further evidence of the wide extent of the Iricoumé Group and coeval volcano-plutonic associations in the central part of the Amazonian Craton.