Disclosing Rhyacian/Orosirian orogenic magmatism within the Guanhães basement inlier, Araçuaí Orogen, Brazil: A new piece on the assembly of the São Francisco-Congo paleocontinent

Abstract

The Guanhães block is one of the basement units present in the context of the Neoproterozoic West Gondwana assembly. It was reworked as a basement inlier within the Araçuaí orogen, in the margins of the São Francisco-Congo (SF-C) paleocontinent. The Guanhães block’s Rhyacian-Orosirian record is revealed for the first time by the Felício and the Mercês granitic plutons. Geophysical, petrographic, lithogeochemical and U-Pb (LA-ICPMS) analyses define and characterize these plutons, and link their genesis to the major Paleoproterozoic orogenic event that is thought to have amalgamated the SF-C paleocontinent. The Felício pluton is composed of mesocratic fine-grained epidote-biotite-granodiorite, the Mercês pluton comprises biotite-monzogranite and hornblende-syenogranite. These two plutons show different geochemical features; the Felício rocks are low-K, magnesian, calcic to calc-alkalic, metaluminous, and the Mercês rocks are rich in K, ferroan, alkali-calcic to alkalic, peraluminous, their shared common features are enrichment in LILE, LREE and HFSE and negative anomalies of Ti, Ta, Nb and P. Zircons collected from the Felício pluton granodiorite yielded a U-Pb concordia age of 2151 ± 12 Ma, interpreted as the pluton’s crystallization age. The Mercês pluton monzogranite yielded a discordia with upper intercept at 2014 ± 11 Ma and lower intercept at 539 ± 13 Ma, interpreted as the Mercês pluton’s cristallization age and the Brasiliano metamorphic overprint, respectively. Trace elements and REE signatures suggest that the magma that originated both plutons shares a common source, compatible with the metasomatization of a mantle wedge by dehydration of a subducted slab. Based on the petrographic, geochemical and geochronological data, the following tectonic scenario is suggested: subduction and accretion of the Mantiqueira arc and emplacement of the Felício pluton at c. 2.15 Ga, followed by collision, gravitational collapse of the orogen, post-collisional magmatism and emplacement of the Mercês pluton at c. 2.01 Ga. This scenario is reinforced by the regional geochemical correlations among the many coeval terranes in the eastern margin of the São Francisco craton, along the Minas-Bahia orogen. At a broader scale, these correlations can be expanded to the African counterpart, giving insights into the SF-C paleocontinent framework in the Precambrian.