Geochronological provinces of the Amazonian Craton

The Amazonian Craton (AC), located in the north of South America, is surrou nded by Neoproterozoic orogenic belts and is divided into six major geochro nological provinces: Central Amazonian -CAP (> 2.3 Ga); Maroni-ltacaiunas-M IP (2.2-1.95 Ga); Ventuari-Tapajos - VTP (1.95-1.80 Ga); Rio Negro-Juruena- RNJP (1.8-1.55 Ga), Rondonian-San Ignacio-RSIP (1.55-1.3 Ga), and Sunsas-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 geochronolog ical pattern indicated that the Archean protocraton of AC consisted for mer ly 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 Ca, while the crustal evolution of SP and part of MIP and RSIP were associated with reworking of the older continental crust. No expo sure 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 mo stly derived from partial melting of Paleoproterozoic and Mesoproterozoic m aterial, suggesting little or no involement of the Archean crust in rite so uthwestern portion of the AC.