This study focuses the granitoids of center-southern portion of Guyana Shield,
southeastern Roraima, Brazil. The region is characterized by two tectono-stratigraphic domains,
named as Central Guyana (GCD) and Uatumã-Anauá (UAD) and located probably in the limits
of geochronological provinces (e.g. Ventuari-Tapajós or Tapajós-Parima, Central Amazonian and
Maroni-Itacaiúnas or Transamazon). The aim this doctoral thesis is to provide new petrological
and lithostratigraphical constraints on the granitoids and contribute to a better understanding of
the origin and geodynamic evolution of Guyana Shield.
The GCD is only locally studied near to the UAD boundary, and new geological data and
two single zircon Pb-evaporation ages in mylonitic biotite granodiorite (1.89 Ga) and foliated
hastingsite-biotite granite (1.72 Ga) are presented. These ages of the protholiths contrast with the
lithostratigraphic picture in the other areas of CGD (1.96-1.93 Ga).
Regional mapping, petrography, geochemistry and zircon geochronology carried out in
the UAD have showed widespread paleoproterozoic calc-alkaline granitic magmatism. These
granitoids are distributed into several magmatic associations with different paleoproterozoic
(1.97-1.89 Ga) ages, structural and geochemical affinities. Detailed mapping, petrographic and
geochronological studies have distinguished two main subdomains in UAD. In the northern
UAD, the high-K calc-alkaline Martins Pereira (1.97 Ga) and Serra Dourada S-type granites
(1.96 Ga) are affected by NE-SW and E-W ductile dextral shear-zones, showing coexistence of
magmatic and deformational fabrics related to heterogeneous deformation. Inliers of basement
(2.03 Ga) crop out to northeastern part of this area, and are formed by metavolcano-sedimentary
sequence (Cauarane Group) and TTG-like calc-alkaline association (Anauá Complex). Xenoliths
of meta-diorites (Anauá Complex) and paragneisses (Cauarane Group) reinforce the intrusive
character of Martins Pereira Granite. On the other hand, xenoliths of Martins Pereira and biotitebearing
enclaves are founded in the younger, undeformed, and SiO2-rich Igarapé Azul Granite
(1.89 Ga). This last and the high-K calc-alkaline Caroebe Granite (1.90-1.89 Ga, Água Branca
Suite), including coeval volcanic rocks (1.89 Ga, Jatapu volcanics) and charnockitoids (1.89 Ga,
e.g. Santa Maria Enderbite), crop out in the southern UAD. This subdomain is characterized only
by local and slight NE-SW ductile-brittle dextral shear zones. A-type granites such as Moderna
(ca. 1.81 Ga) and Mapuera (ca. 1.87 Ga) granites, cross cut both areas of UAD. Furthermore, the
geological mapping also identified three main types of metalotects in this region. Gold mineralization is observed in Martins Pereira-Serra Dourada granitoids (northern UAD), alluvial
columbite-tantalite is related to Igarapé Azul granitoids (southern UAD), and amethyst is
associated to pegmatites from Moderna A-type granites.
The Nd-Pb isotope data suggest that all granitoids of UAD are generated by reworking of older
and pre-existence crustal sources (sialic Rhyacian-Archean and/or juvenile Transamazonian
origin) and mantle input is not problably a viable model. Although the dominant process may be
one subduction in the early stage of NUAD evolution, post-colisional magmatism may be a
significant process in the production of new continental crust in the southern UAD. It is possible
that, following oceanic closure in the Anauá arc system (2.03 Ga) and subsequent collisional
orogeny (1.97-1.94 Ga?), underplated mantle melts (basalt liquids) were trapped below preexisting
lower crustal rocks of various compositions (e.g. granulites, metatonalites, amphibolites).
The basalt liquids and subsequently melted lower crust could produced the immense volumes of
granite (and volcanics) observed at 1.90-1.87 Ga. This geological picture is similar to the Tapajós
Domain (TD) in the southern Amazonian Craton and suggest that both belongs to the same
province (Ventuari-Tapajós or Tapajós-Parima). Nevertheless, the scarcity of S-type granites and
high-grade metamorphic rocks show that the collisional stage is not so evident in TD.
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