An outline of Paleoproterozoic-Mesoproterozoic crustal evolution of the NW Amazon craton and implications for the Columbia Supercontinent

Abstract

ABSTRACT The Rio Negro Province in the NW Amazon craton is composed of three domains (northeastern, central, and southwestern) in turn separated into several regional terrains, showing main NE-SW and WNW-ESE structures and being composed of high-grade polydeformed basement with 1840–1700 Ma protolith ages. The Northeastern Domain shows basements dominated by high-K calc-alkaline to shoshonitic metagranitoids, orthogneisses, migmatites, augen gneisses, and local A-type leucogneisses (1810–1760 Ma, Cauaburi Complex). In Venezuela, this basement is not widely known, but encompasses the oldest rocks of the province (1840–1820 Ma, San Carlos Metamorphic Terrane). The Southwestern Domain comprises medium- to high-K calc-alkaline orthogneisses (Querari Complex) with an extended compositional range (diorite to granite), NE-trending main foliation, and 1740–1700 Ma protolith ages. The Central Domain comprises peraluminous crustal-derived granites (1520–1480 Ma), supracrustal rocks, paragneisses, and some Cauaburi Complex inliers. The Nd isotope data for the basement rocks indicates mantle sources with decreasing crustal contributions and younger TDM ages from east (2.54–1.96 Ga) to west (1.97–1.82 Ga). The Rio Negro Province is interpreted as an accretionary orogen formed by a long-lived magmatic arc system active during three phases: 1.84–1.82 Ga, 1.81–1.76 Ga (main flare up) and 1.75–1.70 Ga. Later, this arc system was affected by collisional orogenies at ~1500 Ma (Içana Orogeny) and ~1300 Ma (Putumayo Orogeny), as showed by the Ar–Ar step heating plateau ages (biotite, hornblende) and U-Pb SHRIMP ages (zircon, titanite) recording two main metamorphic events at 1520–1480 Ma (medium–high T) and 1400–1310 Ma (low–medium T), with important tectonothermal effects also further east in the Tapajós-Parima Province. Based on similar accretionary histories, the Rio Negro Province has also apparent long-lived connections with Laurentia and Baltica (Transscandinavian Belt), forming the core of the Columbia Supercontinent.