Geochronological provinces of the Amazonian Craton

Abstract

The Amazonian Craton (AC), located in the north of South America, is surrounded by Neoproterozoic orogenic belts and is divided into six major geochronological provinces: Central Amazonian -CAP (> 2.3 Ga); Maroni-Itacaiúnas - MIP (2.2-1.95 Ga); Ventuari-Tapajós - VTP (1.95-1.80 Ga); Rio Negro-Juruena - RNJP (1.8-1.55 Ga); Rondonian-San Ignácio - RSIP (1.55-1.3 Ga), and Sunsás - SP (1.3-1.0 Ga). Sr, Pb and Nd isotopic compositions of igneous and orthogneissic rocks from the AC show that a significant addition of new crustal material from the upper mantle occurs during the Paleo- and Mesoproterozoic. The geochronological pattern indicated that the Archean protocraton of AC consisted formerly of independent microcontinents that were amalgamated by Paleoproteorozic orogenic belts, between 2.2 and 1.95 Ga. Part of the MIP and RSIP, and the whole of VTP and RNJP evolved by addition of juvenile magmas to the crust from 1.95 to 1.4 Ga, while the crustal evolution of SP and part of MIP and RSIP were associated with reworking of the older continental crust. No exposure of the Archean crust is known in RSIP and SP, and the Sm-Nd model ages of granitoids from those provinces indicate that the reworked crust was mostly derived from partial melting of Paleoproterozoic and Mesoproterozoic material, suggesting little or no involvement of the Archean crust in the southwestern portion of the AC.