An overview of Rhyacian continental magmatic arcs of the southeastern Guiana Shield, Amazonian Craton

Abstract

The southeastern Guiana Shield comprises an extensive orogenic belt formed during the Rhyacian period. In its Brazilian portion (Amapá and northwestern Pará), this belt includes the Rhyacian Carecuru and Lourenço domains, which are located to the north and south of the Amapá Block, an Archean terrane that was significantly reworked during the Rhyacian orogeny. This paper provides an overview of field, petrographic, geochemical, isotopic, and geochronological data supporting the recognition of continental magmatic arcs that developed during a long-lived (∼170 Ma) evolution of the accretionary stage of the Rhyacian orogeny. In the Lourenço Domain, arc magmatism persisted from 2.26 to 2.09 Ga, while in the Carecuru Domain, it spanned from 2.19 to 2.14 Ga. The studied arc-related rocks mainly consist of calc-alkaline to high-K calc-alkaline granitoids and gneisses, most of which are metaluminous, I-type, and have high contents of large-ion lithophile elements (LILE). The Archean crustal contributions to the origin of the magmas have significantly shaped their isotopic signatures, highlighting the influence of the nearby Amapá Block. The magmatic evolution in Lourenço and Carecuru domains was marked by episodic flare-ups around 2.19–2.18 Ga and 2.14 Ga, indicating periods of intensified activity typical of continental arc systems. This dynamic evolution resembles tectonic settings with long-lived arc magmatism punctuated by episodes of increased activity. Overall, the data suggest that the Rhyacian orogeny in this part of the Amazonian Craton involved tectonic processes similar to those of modern plate tectonics, characterized by prolonged arc magmatism, episodic flare-ups, and crustal interactions, pointing to a complex tectonic environment.