Nd isotopic composition of Paleoproterozoic volcanic and granitoid rocks of Vila Riozinho: implications for the crustal evolution of the Tapajos gold province, Amazon craton

摘要

Nd data from the Paleoproterozoic magmatic rocks of Vila Riozinho and Jamanxim (Tapajos gold province) indicate that original magmas were not produced exclusively by the remelting of Archean sialic crust and point to dominant Paleoproterozoic sources. ε_(Nd)(T) values preclude derivation from mantle sources for the ca. 2.0 Ga Vila Riozinho volcanics and older Sao Jorge granite. They may represent a subduction-related magmatic arc with magmas modified by interaction with crust or a post- to late-orogenic remelting of an older Paleoproterozoic juvenile arc with minimal contribution from the Archean crust. The origin of the 1.88 Ga Parauari, Maloquinha, Iriri, and Moraes Almeida igneous associations and the Jamanxim rhyolites has been attributed to large-scale taphrogenesis that marked the breakup of a large Paleoproterozoic continent. Derivation of the original magmas from the remelting of crustal sources older than ca. 1.9 Ga is consistent with geochemical and Nd isotopic data. Archean remnants probably occur between the Paleoproterozoic terrains of the Ventuari-Tapajos province. Archean terrains of the Amazon craton extend from the Xingu to the Itaituba region but have not been identified in the southern Guyana shield. Thus, data reveal that the boundaries between the central Amazon and Ventuari-Tapajos provinces need better definition and more detailed field and geochronological work.