Geochronological and geochemical evidences for extension-related Neoarchean granitoids in the southern São Francisco Craton, Brazil

- Long period of Neoarchean high-K granitoid magmatism (ca. 100 my).
- 2.73-2.65 Ga A2-type granitoids in the southern São Francisco Craton.
- Reworking of Mesoarchean crust with involvement of juvenile material.
- Crustal reworking in an extensional setting.

New LA-SF-ICP-MS U-Pb zircon dating of high-K granitoids from the Campo Belo metamorphic complex, southern São Francisco Craton (Brazil), reveals a long period (ca. 100 My) of Neoarchean granitic magmatism that post-date the TTG magmatism. The oldest studied pluton is a highly porphyritic biotite orthogneiss emplaced at 2748 ± 5 Ma, followed by a hornblende-biotite orthogneiss (2727 ± 7 Ma). Both granitic bodies were affected by a deformation event prior to the emplacement of the Rio do Amparo, Bom Sucesso and Lavras granitoid plutons at 2716 ± 6 Ma, 2696 ± 6 Ma and 2646 ± 5 Ma, respectively. The Neoarchean granitic magmatism ended with the intrusion of peraluminous leucogranitic dikes at 2631 ± 4 Ma.The 2.73-2.65 Ga Campo Belo granitoids share chemical features of A-type granites, such as high apatite- and zircon-saturation temperatures (mostly > 800 °C), relatively high Fe-number, high total alkalis and characteristic enrichment in LREE and HFSE although most samples of the Rio do Amparo granite have lower HFSE and LREE content that typical A-type granites but very high Th. The high Th content of the Rio do Amparo and Bom Sucesso granites may suggest involvement of Th-orthosilicate in their sources. The trace element composition permits to classify the Campo Belo granitoids as A2-type granites, suggesting derivation from partial melting of TTG-crustal sources likely in an extensional setting.Significant reworking of Mesoarchean crust is suggested by mostly negative εNdi values (Rio do Amparo: −2.0 and +3.1; Bom Sucesso: −3.6, −3.1 and +0.9; Lavras: −2.5 and −0.2) and old Nd model ages (TDM close to 3.1 Ga), although with probable involvement of juvenile material (TDM of 2.7-2.9 Ga). This contrasts with Neoarchean granites of the northern São Francisco and Congo cratons characterized by negligible juvenile imprint.The 2.75-2.63 Ga Campo Belo granitoids witness the thermal stabilization of the Archean lithosphere through a major episode of high-K granitoid magmatism between 2760 and 2600 Ma, which affected the whole São Francisco Craton and the northern Congo Craton.