Crustal growth in the northeast portion of the Rhyacian Bacajá domain, SE Amazonian craton, based on U-Pb, Lu-Hf, and Sm-Nd data

Abstract

The Bacajá domain, southeastern Amazonian craton, comprises Mesoarchaean and Siderian terrains reworked during the Transamazonian cycle. Combined analyses of zircon LA-ICP-MS U-Pb and Lu-Hf with whole-rock Sm-Nd from the northeast portion of this domain made it possible to propose an evolutionary sequence between ca. 2.60 and 2.06 Ga. Gneisses with an igneous protolith age of 2630 ± 15 Ma show negative signatures ( ɛ Hf (t) = -0.3 to -1.7 and ɛ Nd (t) = -3.08 to -2.98) and a Mesoarchaean formation (Hf-T DMC and Nd-T DM model ages range from 3.0 to 3.2 Ga). Rhyacian granite genesis lasted about 40 million years (2.10–2.06 Ga) and was divided into two magmatic periods. The first is represented by deformed granitoids with zircons yielding crystallization ages between 2.10 and 2.09 Ga and model ages (Hf-Nd) at about 2.5 Ga. The second event is represented by granitoids with preserved magmatic texture, crystallization ages of 2.06 Ga, and Siderian model ages (Hf-Nd) of around 2.3 Ga. The overall Hf isotopic analyses of this Rhyacian granite genesis exhibit a spread of ɛ Hf (t) values between 1.8 and -2.9, which show a probably underestimated mantle-derived contribution in this period.