Petrogenesis of the Paleoproterozoic (Orosirian) A-type granites of Carajas Province, Amazon Craton, Brazil: Combined in situ Hf-O isotopes of zircon

We present new Lu-Hf and Oxygen isotopic analyses and complementary whole-rock Nd isotopic data for three A-type Paleoproterozoic suites (1880 Ma to 1857 Ma; Serra dos Carajas, Velho Guilherme, and Jamon) and related granites of the Carajas Province, eastern Amazon Craton, Brazil. Zircon grains from all the granites have remarkably restricted initial Hf-176/Hf-177 and strongly negative epsilon Hf(t) values ranging from 9 to 18, and 6180 fairly homogeneous varying from 5.50%. to 7.00 parts per thousand. Small differences were observed internally in the plutons or between them. These differences can result for contrasts in the crustal domains of the Carajas Province that were the source of the granites or of local contamination processes. Hf model ages indicate Paleoarchean sources (3.3 Ga to 3.6 Ga) with a minor contribution from Mesoarchean (3.0 Ga to 3.2 Ga) melts for these granites. This model ages are older than the exposed Archean country rocks of the Orosirian granites of the Carajas Province and more investigation is needed to verify the real existence of that older Archean crust. On the other hand, Nd isotope data and geochemical-petrological studies indicate that the Carajas granites derived from Mesoarchean granitoid sources and this hypothesis should be retained. The studied samples have Hf-O isotopic compositions that overlap within error, and evidence of contamination (crustal assimilation or mixing) for a mantle-derived magma cannot be seen. These plutons crystallized from magmas generated by melting of pre-existing igneous rocks with possibly in the Velho Guilherme Suite a minor contribution from a supracrustal (metasedimentary) component is envisaged. The Nd, Hf, and 0 isotope compositions of the Paleoproterozoic granites of Carajas Province clearly attest to an igneous ancient crustal source in the origin of their magmas. This anorogenic granites represent a large volume of granitic magmatism generated in the late Palaeoproterozoic in the eastern of the Amazon Craton. This work shows the importance of the Archean source in the generation of the A-type Paleoproterozoic granites from Carajas province. These granites are an example of A-type granites derived essentially from crustal sources without significant influence of mantle magmas except as a source of heat. (C) 2019 Elsevier B.V. All rights reserved.